ASIAA Colloquium is usually held on Wednesdays at 2:20-3:20 pm in Room 1203 of the Astronomy-Mathematics Building, NTU. All scientists are welcome to attend. Seminars on more specialized topics are also held on a regular basis. Some talks are recorded and shared on Youtube channel.
The ASIAA-NTU joint colloquium series aims to bring to the physics/astronomy/cosmology community in ASIAA/NTU world renown researchers who will talk about the forefront development of physical sciences.
Exquisite observations from JWST are allowing us to extract
multidimensional, time varying, properties of distant planetary
atmospheres, giving us an exciting opportunity to understand how
planets work. Alongside this, the drive to determine the possibility
of life beyond Earth continues to shape our field. However, these
efforts require extensive investment in forward, physical, modelling
to truly understand what is actually going on! We have been working to
simulate planets from the Early Earth during the Archean, when life
was first present, to Mars and on to exoplanets. For this talk, I will
focus on simulations including chemical kinetics, clouds and hazes for
hot Jupiters and will discuss how these processes shape the potential
observations, highlighting areas requiring further work and
constraint. Then, I will move to biotic modelling, attempting to use
simplified models informed by Earths own biosphere evolution to help
guide the search for life beyond Earth
Next Seminar:
2026-11-18 Wed 14:20~15:20 [R1203]
Speaker:
Mason Ng (McGill University)
Topic:
Millisecond Flashes from Across the Universe: What Polarization Reveals About Fast Radio Bursts
Abstract:
The radio sky varies on timescales from microseconds to years, and the transient classes discovered in recent decades are some of the most extreme known. Among them are fast radio bursts (FRBs), millisecond-duration radio flashes with spectral luminosities comparable to active galactic nuclei yet their origins remain unknown. In this talk, I will briefly place FRBs in the broader landscape of radio transients and introduce the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which has now detected thousands of FRBs. I will then focus on how polarization probes both the emission mechanism of FRBs and the magnetized environments that FRBs travel through, including early results on depolarization and on the relationship between the rotation measure and dispersion measure across a subset of the FRB population. I will close with the prospects for precise localizations with the CHIME/FRB Outriggers and the SKA, which will connect FRBs to their host galaxies and local environments, and open the door to using them as probes of cosmic magnetism.
Next Colloquium:
2026-11-19 Thu 14:20~15:20 [R1203]
Speaker:
Nathan Mayne (University of Exeter)
Topic:
Abiotic & Biotic Climates
Abstract:
Exquisite observations from JWST are allowing us to extract multidimensional, time varying, properties of distant planetary atmospheres, giving us an exciting opportunity to understand how planets work. Alongside this, the drive to determine the possibility of life beyond Earth continues to shape our field. However, these efforts require extensive investment in forward, physical, modelling to truly understand what is actually going on! We have been working to simulate planets from the Early Earth during the Archean, when life was first present, to Mars and on to exoplanets. For this talk, I will focus on simulations including chemical kinetics, clouds and hazes for hot Jupiters and will discuss how these processes shape the potential observations, highlighting areas requiring further work and constraint. Then, I will move to biotic modelling, attempting to use simplified models informed by Earths own biosphere evolution to help guide the search for life beyond Earth
Next Seminar:
2026-11-20 Fri 11:00~12:00 [R1203]
Speaker:
Robert Andrassy (HITS)
Topic:
Radiation hydrodynamics of stellar interactions and stellar interiors
Abstract:
The common-envelope phase of stellar evolution occurs when an evolved star expands into giant dimensions and engulfs a nearby and much more compact companion. A dynamical interaction ensues, in which gravitational drag dramatically reduces the binary separation, potentially explaining the formation of compact binaries. Three-dimensional, adiabatic simulations show that the envelope of the giant may be fully ejected, especially if recombination energy is taken into account. Radiative energy losses are likely to be important in reality and early radiation hydrodynamic simulations indeed point to less efficient mass ejection. I will describe our work towards studying common envelope evolution using a radiation hydrodynamics scheme implemented in the moving-mesh code Arepo.
In the second half of this seminar, I will focus on the physics of core convection in upper main sequence stars, in which interaction between hydrodynamic flows and radiation is equally important. It turns out that a thermal-timescale process known as convective penetration can substantially increase the mass of the mixed core beyond predictions of linear stability theory, potentially explaining core sizes derived from observational data. We quantify the penetration distance in a simplified model of a 15 M_Sun star using multidimensional simulations performed using our time-implicit code SLH. Our results converge upon grid refinement and are broadly consistent with observations.
Exquisite observations from JWST are allowing us to extract
multidimensional, time varying, properties of distant planetary
atmospheres, giving us an exciting opportunity to understand how
planets work. Alongside this, the drive to determine the possibility
of life beyond Earth continues to shape our field. However, these
efforts require extensive investment in forward, physical, modelling
to truly understand what is actually going on! We have been working to
simulate planets from the Early Earth during the Archean, when life
was first present, to Mars and on to exoplanets. For this talk, I will
focus on simulations including chemical kinetics, clouds and hazes for
hot Jupiters and will discuss how these processes shape the potential
observations, highlighting areas requiring further work and
constraint. Then, I will move to biotic modelling, attempting to use
simplified models informed by Earths own biosphere evolution to help
guide the search for life beyond Earth
Shang-Min Tsai
2026-11-18 Wed 14:20~15:20 R1203
Mason Ng McGill University
*Seminar* Millisecond Flashes from Across the Universe: What Polarization Reveals About Fast Radio Bursts
Millisecond Flashes from Across the Universe: What Polarization Reveals About Fast Radio Bursts
The radio sky varies on timescales from microseconds to years, and the transient classes discovered in recent decades are some of the most extreme known. Among them are fast radio bursts (FRBs), millisecond-duration radio flashes with spectral luminosities comparable to active galactic nuclei yet their origins remain unknown. In this talk, I will briefly place FRBs in the broader landscape of radio transients and introduce the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which has now detected thousands of FRBs. I will then focus on how polarization probes both the emission mechanism of FRBs and the magnetized environments that FRBs travel through, including early results on depolarization and on the relationship between the rotation measure and dispersion measure across a subset of the FRB population. I will close with the prospects for precise localizations with the CHIME/FRB Outriggers and the SKA, which will connect FRBs to their host galaxies and local environments, and open the door to using them as probes of cosmic magnetism.
Kai-Yang Lin
2026-11-19 Thu 11:00~12:00 R1203
Max Heller HITS
*Seminar* Simulating stellar interactions: 1D stellar mergers and 3D common envelopes
Simulating stellar interactions: 1D stellar mergers and 3D common envelopes
Most massive stars, and a large fraction of all stars, reside in binary or higher-order systems, and many of them interact during their lifetimes. Two of the most consequential interactions are stellar mergers and common envelope (CE) events. Both are inherently three-dimensional, and thus in applications such as population synthesis treated in a parametrized way. I will present two complementary approaches: fast 1D methods that approximate the outcome of stellar mergers, and 3D simulations of CE events that can inform simplified prescriptions.
In the first part, I will give a short introduction to the physics and numerical modelling of common envelopes (CEs). I then present a grid of CE simulations performed with the moving-mesh code Arepo, followed over many dynamical timescales until the envelope is ejected. The grid varies the primary mass, evolutionary stage and mass ratio. I show how the final separation and ejection efficiency depend on these parameters, and what this implies for CE prescriptions in population synthesis.
In the second part, I will discuss 1D methods for constructing merger remnants. These range from sorting the progenitors' shells by entropy to the MMAMS ("Make Me A Massive Star") approach, which adds shock heating calibrated on smoothed particle hydrodynamics (SPH) simulations of stellar head-collisions. I compare these methods against another set of 3D head-on stellar collisions simulated with SPH and show that MMAMS outperforms entropy sorting in reproducing the remnant’s entropy and composition profiles for most of the tested cases.
2026-11-19 Thu 14:20~15:20 R1203
Nathan Mayne University of Exeter
*Colloquium* Abiotic & Biotic Climates
Abiotic & Biotic Climates
Exquisite observations from JWST are allowing us to extract multidimensional, time varying, properties of distant planetary atmospheres, giving us an exciting opportunity to understand how planets work. Alongside this, the drive to determine the possibility of life beyond Earth continues to shape our field. However, these efforts require extensive investment in forward, physical, modelling to truly understand what is actually going on! We have been working to simulate planets from the Early Earth during the Archean, when life was first present, to Mars and on to exoplanets. For this talk, I will focus on simulations including chemical kinetics, clouds and hazes for hot Jupiters and will discuss how these processes shape the potential observations, highlighting areas requiring further work and constraint. Then, I will move to biotic modelling, attempting to use simplified models informed by Earths own biosphere evolution to help guide the search for life beyond Earth
Shami Tsai
2026-11-20 Fri 11:00~12:00 R1203
Robert Andrassy HITS
*Seminar* Radiation hydrodynamics of stellar interactions and stellar interiors
Radiation hydrodynamics of stellar interactions and stellar interiors
The common-envelope phase of stellar evolution occurs when an evolved star expands into giant dimensions and engulfs a nearby and much more compact companion. A dynamical interaction ensues, in which gravitational drag dramatically reduces the binary separation, potentially explaining the formation of compact binaries. Three-dimensional, adiabatic simulations show that the envelope of the giant may be fully ejected, especially if recombination energy is taken into account. Radiative energy losses are likely to be important in reality and early radiation hydrodynamic simulations indeed point to less efficient mass ejection. I will describe our work towards studying common envelope evolution using a radiation hydrodynamics scheme implemented in the moving-mesh code Arepo.
In the second half of this seminar, I will focus on the physics of core convection in upper main sequence stars, in which interaction between hydrodynamic flows and radiation is equally important. It turns out that a thermal-timescale process known as convective penetration can substantially increase the mass of the mixed core beyond predictions of linear stability theory, potentially explaining core sizes derived from observational data. We quantify the penetration distance in a simplified model of a 15 M_Sun star using multidimensional simulations performed using our time-implicit code SLH. Our results converge upon grid refinement and are broadly consistent with observations.
2026-11-23 Mon 11:00~12:00 R1203
Damien Gagnier HITS
*Seminar* Common-envelope evolution: from 3D simulations to dynamical friction theory
Common-envelope evolution: from 3D simulations to dynamical friction theory
Common-envelope evolution is a key phase in the formation of many compact binary systems, yet its dynamics remain difficult to predict from first principles. During the inspiral, the embedded companion exchanges energy and angular momentum with the stellar envelope through gravitational torques and dynamical friction, while accretion, turbulence, and magnetic fields can further affect the evolution. In this talk, I will present a series of numerical and analytical studies aimed at understanding these processes across the different stages and spatial scales of common-envelope evolution. I will first discuss three-dimensional hydrodynamic and magnetohydrodynamic simulations of the long-lived post-dynamical inspiral. These simulations reveal a complex redistribution of angular momentum by large-scale flows and turbulence, strong variability and accretion around the central binary, and efficient amplification of initially weak magnetic fields by differential rotation and turbulent motions. They also show how the gas surrounding the binary progressively settles into a nearly corotating, quasi-hydrostatic structure, strongly reducing the subsequent rate of orbital decay. I will then focus on the earlier, dynamical phase of the inspiral and on the gravitational interaction between an embedded companion and its surrounding gas. Local simulations show how density stratification, stellar rotation, and accretion modify the gravitational wake, the drag, and transverse forces acting on the companion. Finally, I will present a complementary (semi-)analytical approach to dynamical friction in spherical, stratified stellar envelopes. By describing the wake as the global acoustic response of the star to an orbiting perturber, this framework makes it possible to quantify departures from standard local, uniform-medium prescriptions and to follow the resulting orbital evolution. Together, these studies connect global common-envelope dynamics to the local physics of the embedded companion and provide steps toward predictive, computationally inexpensive models of common-envelope and planetary-engulfment evolution.
2026-11-24 Tue 11:00~12:00 R1203
Marco Vetter HITS
*Seminar* Magnetic fields, microphysics, and moving boundaries: improving 3D models of common-envelope evolution
Magnetic fields, microphysics, and moving boundaries: improving 3D models of common-envelope evolution
Common-envelope (CE) evolution is thought to be central to the formation of many close binaries. Many aspects of it remain open, and three-dimensional simulations are still far from capturing the full physical picture of this dynamic interaction. In this seminar I will give an overview of three lines of work we have been pursuing to improve our modelling approaches and deepen our understanding of the CE phase.
First, I will show how magnetic fields are amplified during the inspiral of the companion in our magnetohydrodynamic simulations. I will also discuss how they may affect the outcome of the interaction and the structures that emerge from it, such as the disks that form around the remnant binary and the outflows associated with them.
Second, I will introduce PIG, a tabulated equation of state for partially ionized gas that includes molecular hydrogen. It is built on the Helmholtz free-energy framework of Timmes & Swesty, so codes that already use the Helmholtz EoS can adopt it with only small changes, and it is thermodynamically consistent by construction. It is designed to capture the main effects of ionization and H₂ dissociation in multidimensional simulations at the cost of a table interpolation. In our CE simulations, it allows the ejecta to be followed to lower temperatures and densities than the OPAL tables cover.
Third, I will discuss recent developments in moving-boundary approaches. In most 3D CE simulations, the core of the giant is replaced by a softened point mass that interacts with the envelope only through gravity. This avoids the very short timescales of the core, but the approximation itself can affect the outcome of the simulation, such as the final orbital separation, and it prevents the core from reacting to the removal of the envelope. Replacing the core region with an inner boundary that moves with and responds to the surrounding flow is one way to include this reaction without resolving the core itself.
2026-11-24 Tue 14:20~15:20 R1203
Salvatore Orlando INAF
*Colloquium* From Stellar Death to Supernova Remnants: Bridging Core-Collapse Explosions and Their Multiwavelength Signatures
From Stellar Death to Supernova Remnants: Bridging Core-Collapse Explosions and Their Multiwavelength Signatures
Core-collapse supernovae mark the explosive deaths of massive stars, but the physical processes initiated by the explosion continue to shape their surroundings for thousands of years. The expanding stellar debris interact with the circumstellar material shaped by the progenitor's late evolutionary stages and, eventually, with the interstellar medium, giving rise to supernova remnants whose complex structures and emission encode a wealth of information about both the progenitor star and the explosion mechanism.
In this talk, I will illustrate how three-dimensional hydrodynamic and magnetohydrodynamic simulations provide a powerful framework for linking the final evolutionary stages of massive stars and the physics of core-collapse explosions to the observable properties of supernova remnants. Focusing on the Galactic remnants Cassiopeia A and SN 1987A, as well as the extragalactic supernova SN 2014C, I will show how numerical models, combined with multiwavelength observations, can shed light on the evolutionary history of these systems and help interpret their complex morphologies and emission properties. Particular attention will be devoted to the interaction between supernova ejecta and circumstellar material, shock evolution, and particle acceleration. These examples will demonstrate how numerical simulations and observations can be combined to probe the explosion physics and reconstruct the final evolutionary stages of massive stars.
2026-11-25 Wed 11:00~12:00 R1203
Peter Siu Hei Cheung HITS
*Seminar* From Stable Envelopes to Core Collapse: Over-contact Binaries, Common Envelopes, and Accretion-Induced Collapse
From Stable Envelopes to Core Collapse: Over-contact Binaries, Common Envelopes, and Accretion-Induced Collapse
The evolutionary trajectory of close binary star systems depends fundamentally on the stability of mass transfer during Roche lobe overflow. I will introduce three different scenarios including the structural evolution of synchronized over-contact systems, the asymmetric ejections in a common envelope interaction that shape bipolar planetary nebulae, and the subsequent core-collapse of massive white dwarfs via accretion-induced collapse.
In a stable mass-transferring system, an over-contact binary can share a stable envelope over nuclear timescales. In the first part of the talk, I will present new hydrodynamic simulations of an over-contact binary. Various observations suggest that the binaries have an equal surface temperature. I will show that the hydrodynamical flow driven by Coriolis force can introduce a fast mixing in an initially hydrostatic equal-mass contact binary. This rotation-driven flow may explain the equal surface temperature observed.
A binary system will enter a dynamical common envelope evolution phase if the mass transfer is unstable. The asymmetric morphology of bipolar planetary nebulae, for example the Calabash Nebula, points to an origin involving binary star interactions. Their characteristic shapes may be linked to the interplay between a fast wind from the central engine and the dense, toroidal disk remnant from common-envelope evolution. In the second part of the talk, I will present some planetary nebula simulations based on restarting previous common-envelope evolution simulations with a continuous driving wind in AREPO.
After the common envelope phase, a white dwarf may accrete enough mass and undergo accretion-induced collapse. The central remnant may have a magnetar-level magnetic field if the white dwarf progenitor holds a strong enough magnetic field. In the final part of the talk, I will present the magnetohydrodynamic simulations of accretion-induced collapse of rotating white dwarfs with self-consistent initial magnetic progenitors. Our findings show that with initial surface magnetic field strength constrained by isolated white dwarf observations (100-1000 MG), the protoneutron star can reach field strength consistent with magnetar observations.
2026-11-25 Wed 14:20~15:20 R1203
Gil Holder UIUC
*Colloquium*
Yi-Kuan Chiang
2026-11-26 Thu 14:20~15:20 R1203
Mike Lau HITS
*Seminar* Capturing the fleeting interactions of stellar binaries
Capturing the fleeting interactions of stellar binaries
Half of Sun-like stars are in binaries and massive stars are mostly in triple and higher-order systems. The majority of binaries contain stars close enough that they would interact at some point in their lives. These interactions are central to many fields of astronomy and are crucial in the formation of X-ray binaries, gravitational wave sources, Type Ia supernova progenitors, planetary nebulae, and more.
I will give an overview of my work on stellar interactions occurring on the short dynamical timescale, which are rarely observed directly but whose physics and outcomes are deeply uncertain. These phases include common-envelope evolution, mass transfer, planetary engulfment, and stellar mergers. Recently, we published one of the first 3D radiation-hydrodynamic simulations of common-envelope evolution. I will discuss how radiation-transport effects may challenge the standard picture and present the first synthetic photometry obtained self-consistently from 3D simulations, which constitutes a major step towards interpreting luminous red novae. I will then give an overview of uncertainties surrounding mass transfer from the perspective of binary evolution, presenting results from stellar-evolution and 3D hydrodynamical models. Finally, I will present ongoing work on modelling the long-term evolution of stellar mergers, connecting 3D simulations with 1D models and explaining the formation of long-lived blue supergiants.
Even “single” stars can experience dynamical interactions not with another star, but with their planet(s). Planetary engulfment could lead to chemically peculiar stars, such as lithium-rich giants, and rapidly rotating stars. In recent work, we performed simulations that revealed that engulfed giant planets lose mass in a continuous process. This mode of mass loss could enable chemical pollution in early-stage giant stars, which were previously thought to avoid pollution when assuming engulfed planets are catastrophically disrupted beneath the stellar convective envelope.
2026-12-02 Wed 14:20~15:20 R1203
Salvatore Orlando INAF
*Colloquium*
2026-12-09 Wed 14:20~15:20 R1203
Toshiki Kurita MPA
*Colloquium*
Teppei Okumura
2026-12-15 Tue 14:20~15:20 R1203
Keiichi Maeda Kyoto U.
*Colloquium*
2026-12-16 Wed 14:20~15:20 R1203
Kei Ito Technical University of Denmark
*Colloquium*
Wei-Hao Wang, Bovornpratch Vijarnwannaluk
Past talks in 2026
2026-01-07 Wed 14:20~15:20 R1412
Kinwah Wu UCL
*Colloquium* Black holes in molecular clouds
Black holes in molecular clouds
Molecular clouds are cradles of star-formation, yet black holes are
the ultimate end products of stellar evolution. Molecular clouds are
diffuse media spanning a wide range of parameters, while astrophysical
black holes are extreme compact objects specified only by their mass
and spin. Most studies of molecular clouds would not include any black
holes in the consideration, and most studies of black holes of stellar
origins are not associated with any molecular clouds. This work will
explore what black holes "would do" when residing in and traversing
across a molecular cloud and how their actions would impact on the
structures and determine fate of their host molecular clouds. We will
first show that the encounter of black hole and molecular clouds are
not rare occasions but more frequent than we would expect if we take
the face value of abundance of molecular clouds and the populations
of stellar remnant black holes in our Galaxy. We will discuss the
accretion of gas by black holes in molecular and their observational
signatures, and the impacts on a molecular cloud when it is embedded
with one or multiple black holes.
2026-01-12 Mon 10:00~11:00 R1203
Karl Schuster IRAM
*Colloquium* IRAM and the Status of the IRAM observatories, NOEMA and the 30m Telescope
IRAM and the Status of the IRAM observatories, NOEMA and the 30m Telescope
A presentation of IRAM, the Institute for Radio Astronomy in the Millimeter range in Grenoble France will be made. After a brief description of IRAM's mission, organization, and key figures, the presentation will cover IRAM's facilities, including its laboratories and observatories.
In the following, a more detailed overview of the status of the IRAM observatories—the Northern Extended Millimeter Array (NOEMA) and the IRAM 30-meter telescope—will be given. Recent upgrades and their scientific impact will be described. Some scientific highlights and ongoing technical development for future upgrades will be presented.
2026-01-19 Mon 14:20~15:20 R1412
Soham Mandal University of Virginia
*Seminar* Stellar forensics: tracing the origin of interaction-powered supernovae and Type-Ia supernova remnants
Stellar forensics: tracing the origin of interaction-powered supernovae and Type-Ia supernova remnants
Interaction with the surrounding media provides an important way to learn about the progenitors of supernovae (SNe). A fraction of core-collapse SNe show signs of strong interaction with the circumstellar material (CSM). Rising evidence points to asymmetry and sustained growth (over decades) of the CSM prior to core-collapse. Using a combination of the stellar evolution code MESA, a 3D hydrodynamics code, and a combination of radiation hydrodynamics and radiative transfer methods, I will demonstrate how SNe in binary systems can show signs of strong interaction, and may appear different when viewed from different directions. In the next part of my talk, I will venture ahead to the remnant phase and discuss how interaction in remnants of thermonuclear supernovae (Type-Ia SNRs) reveals the mass of the white dwarf (WD) progenitor. The mass of the WD in turn holds clue to the explosion mechanism, which is still poorly constrained for observed Type-Ia SNe. I will also demonstrate a technique to analyze X-ray and optical observations of SNRs. I will present application of the method to two well-known examples, unveiling whether their progenitor reached the Chandrasekhar mass at explosion.
2026-01-21 Wed 14:20~15:20 R1412
Delaney Dunne Caltech
*Seminar* The CO Mapping Array Project and Joint Analyses for LIM
The CO Mapping Array Project and Joint Analyses for LIM
The current generation of line intensity mapping (LIM) surveys face two primary observational limitations: sensitivity, and systematic errors from instrumental or astrophysical origins. Both of these limitations can be mitigated by combining LIM data with data from external galaxy surveys, which add priors about where signal should be located and are subject to systematic errors independent from those of the LIM survey. I will discuss a robust, simple statistical technique for performing this combination – stacking the LIM data on the positions of the survey galaxies. I will show stacking results from COMAP (the CO Mapping Array Project), a currently-observing LIM experiment targeting dense molecular gas in galaxies via their CO(1-0) emission. I will compare the output from COMAP stacks on quasars from eBOSS and DESI to modelling of the stacked emission and explore the implications of a mild tension between the models and the COMAP-eBOSS/DESI stacked upper limit. This simple method has the potential to illuminate the relationship between line-emitting gas and the large-scale environments of selected galaxy types, providing information beyond the scope of LIM auto-correlation studies.
2026-01-27 Tue 14:30~15:15 R1203
Dr. Lorena Acuña Max Planck Institute for Astronomy (MPIA))
*Seminar* The interiors and atmospheres of sub-Saturn gas giants
The interiors and atmospheres of sub-Saturn gas giants
More than 6000 exoplanets have been discovered, with their masses,
radii, equilibrium temperatures, and atmospheres revealing a remarkable
diversity in planetary properties and compositions. Within this
landscape, sub-Saturn gas giant bridge sub-Neptunes and Jupiter-mass
giants, forming a key population for understanding planetary interiors,
evolution, and formation pathways.
In this talk, I will review the fundamental theory of Solar System and
exoplanet interiors, highlighting the mechanisms that shape the interior
structure of sub-Saturns. I will address how observations and modeling
are combined to constrain their interior compositions and structures. In
particular, I will discuss results from studies based on mass–radius
data, and show how additional constraints - such as age, transmission
and emission spectra, and Love numbers - are emerging from current and
upcoming observations with JWST.
2026-01-28 Wed 14:20~15:20 R202
David M. Hernandez NTNU
*Colloquium* Time-symmetry, solar system chaos, and Earth’s climate history
Time-symmetry, solar system chaos, and Earth’s climate history
To first approximation, the structure of large scale astronomical systems is governed by gravity, which is described by time-reversible ordinary differential equations. I present novel time-symmetric numerical methods for simulations of structure formation which respect this time-symmetry and show they can be significantly more accurate than non-reversible numerical methods in studying gravitational dynamics. One of these methods is being implemented as TRACE in the REBOUND software package, and we find for interesting planetary dynamics problems it offers a speed advantage of an order magnitude or more compared to other codes.
Next, I focus on the effects of stellar flybys on Earth's climate history. Stellar flybys can have notable effects on the solar system's long-term dynamical evolution, injection of Oort cloud comets into the solar system, properties of trans-Neptunian objects, and more. Using a state-of-the-art solar system model, including a lunar contribution and the J2 solar quadrupole, and random stellar parameters, we find no influence of passing stars on paleoclimate reconstructions over the past 56 Myr, in contrast to recent results from other authors who did not include some of these physical effects.
Finally, I tackle the problem of the stability of the Solar System. Although great progress has been made in the last decades towards an understanding of chaos and stability of the Solar System, I show that some studies are affected by numerical artifacts, which causes artificial Solar System chaos and instability. The physical mechanism behind Mercury's orbital instability has been traditionally described by a diffusive process in a secular frequency, but our current work shows a sub-diffusive process fits simulated data better. An explanation for this sub-diffusion remains elusive.
2026-02-03 Tue 11:00~12:00 R1412
William Matthewson KASI
*Seminar* Model-Independent Analysis of DESI Dark Energy Results
Model-Independent Analysis of DESI Dark Energy Results
Our current understanding of the universe relies on the ΛCDM model that includes, among other components, a cosmological constant dark energy (Λ) and cold dark matter (CDM). The large-scale structure of the late universe contains a wealth of information that can be used to test this concordance model, and the second data release of Baryon Acoustic Oscillations from the the Dark Energy Spectroscopic Instrument (DESI) already places impressive constraints on cosmology. In particular, the w0waCDM parametrization of dark energy shows a slight preference for an evolving dark energy component, with an effective phantom behaviour at higher redshifts. If this phenomenological result persists, it would signal a major shift in our understanding, and require a new theoretical description of the universe. However, since this 2-parameter extension of ΛCDM might be prone to bias, or insensitive to certain behaviours, it is important to test the results using more flexible, model-independent reconstructions. I will focus on recent work within DESI where we do this by implementing crossing statistic reconstruction, binning and Gaussian process regression. What we find (SPOILER ALERT!) is a preference for an expansion history consistent with the trends seen in the Key Paper result (arXiv:2503.14738). And, if you are new to cosmology, don't let the jargon in the abstract scare you, I promise it's for official purposes only.
2026-02-03 Tue 14:20~15:20 R1203
Natsuki Funakoshi UCL
*Seminar* Revealing dynamic history and structure of the Milky Way
Revealing dynamic history and structure of the Milky Way
How disc galaxies form and evolve remains a fundamental question in astrophysics. The Milky Way provides a unique opportunity to address this, as we can measure precise positions, motions, and ages of individual stars. In particular, stellar kinematics offer a powerful way to uncover both current dynamical processes and the imprints of past evolution.
In the first part of this work, by combining Gaia DR3 with classical Cepheids, we reveal the kinematic diversity of multiple spiral arms. The Perseus and Outer arms show opposite correlations between radial and azimuthal velocities. Comparison with simulations suggests that these two arms are in distinct evolutionary phases. These findings challenge the classical view of static spiral arms and instead support a dynamic, transient picture of spiral structure in the Milky Way. In the second part, we aim to trace how the Milky Way disc formed over time. Combining an action-based distribution function fitting with APOGEE–Gaia red giant stars with reliable age estimates allows us to reveal age-dependent trends in disc parameters. We identify the transition between the thick and thin disc populations, likely triggered by the Gaia-Sausage-Enceladus (GSE) merger.
Together, these results show how stellar kinematics trace both the formation history and ongoing evolution of the Milky Way, and highlight the potential of future large-scale astrometric and spectroscopic surveys to further resolve its dynamics.
2026-02-04 Wed 14:20~15:20 R202
Masahiro Machida Kyushy University
*Colloquium* From Prestellar Cores to Class II Disks: Numerical Simulations of Star Formation
From Prestellar Cores to Class II Disks: Numerical Simulations of Star Formation
Recent ALMA observations have unveiled a wealth of fine structures in
star-forming regions, such as protostellar outflows and jets,
asymmetric gas accretion, and rotationally supported circumstellar
disks. In addition, ring and gap substructures—often interpreted as
signatures of planet formation—have been identified even during the
active gas accretion phase. In this study, we carried out
magnetohydrodynamic simulations of star formation starting from a
prestellar core, and followed the subsequent formation and evolution
of a protostar and its surrounding disk up to the Class II stage. Our
simulations successfully reproduce the development of outflows and
jets, as well as circumstellar disks exhibiting complex morphologies,
envelopes, and asymmetric accretion flows. By comparing these results
with ALMA observations, we gain insight into the physical processes
governing the earliest stages of star and disk formation. In this
talk, I will present recent progress in our understanding of early
star formation based on comparisons between numerical simulations and
observations.
2026-02-05 Thu 14:20~15:20 R1203
Cheng Chen CITA
*Seminar* Planet formation and evolution around misaligned circumbinary disks
Planet formation and evolution around misaligned circumbinary disks
Recent observations have revealed that circumbinary disks that are misaligned to the binary orbit could be common in the universe. Dissipation in the disk causes it to move either towards coplanar alignment or polar alignment. Since planets form inside disks, circumbinary planets may also form misaligned to the binary orbit. We explore the orbital evolution of the binary with the misaligned circumbinary disk. The disk-binary interaction leads to the evolution of the binary’s orbit, which could either shrink over time due to the loss of its angular momentum via resonances or expand due to the acquirement of specific angular momentum via accretion. We explore diverse parameter domains of circumbinary systems with polar and retrograde disks. Our results have implications in a variety of astrophysical objects, including the orbital evolution of stellar binaries and the evolution of both stellar and supermassive black hole binaries.
2026-02-11 Wed 14:20~15:20 R202
Yuh Tsunetoe SHAO
*Colloquium* Probing Limb-Brightened Jets with Radiative Transfer: Anisotropic Electrons and Slow-Light Effects
Probing Limb-Brightened Jets with Radiative Transfer: Anisotropic Electrons and Slow-Light Effects
Very long baseline interferometry (VLBI) observations show that relativistic jets, such as the one in M87, exhibit a limb-brightened, double-edged structure that has been challenging to reproduce in theoretical models. In this talk, I present a radiative-transfer framework that combines anisotropic electron distributions with “slow-light” treatment, which considers the time-evolution of plasmas during light ray propagation. Motivated by recent particle-in-cell simulations, we assume that nonthermal electron velocities are preferentially aligned with magnetic field lines. Implementing this prescription in general relativistic magneto-hydrodynamic (GRMHD) models, we produce images across multiple frequencies and spatial scales. We find that synchrotron emission is naturally concentrated along helical magnetic fields, producing limb-brightened morphologies from tens of microarcseconds to hundreds of milliarcseconds in the M87 jet. When slow-light radiative transfer is included, loop-like features of the jet are stretched and smoothed, yielding a cone-like, double-edged jet morphology consistent with observations. We further show that jet appearance and variability depend sensitively on black hole spin, offering testable predictions for horizon-scale imaging with next-generation instruments such as EHT, ngEHT, and BHEX.
2026-02-25 Wed 14:20~15:20 R1203
Laurent Loinard UNAM / Harvard
*Colloquium* The Event Horizon Telescope: From the First Image to the First Movie of a Black Hole<br>
The Event Horizon Telescope: From the First Image to the First Movie of a Black Hole
In 2019, the Event Horizon Telescope (EHT) collaboration released the first image of a supermassive black hole: the one residing at the center of the galaxy M87. Since that milestone, the EHT has established a rich legacy that includes the first images of Sagittarius A*, the black hole at the center of the Milky Way; the first images of black hole environments in polarized light—both linear and circular—revealing dynamically important magnetic fields near the event horizon and favoring magnetically arrested disk models; and the first strong evidence for intrinsic time variability in both total intensity and magnetic field structure.
In this colloquium, I will review these key scientific results and discuss the evolution of the EHT array that made them possible. I will conclude by describing ongoing developments and future efforts aimed at obtaining the first time-resolved “movie” of a black hole, probing horizon-scale dynamics on timescales comparable to the characteristic timescales of the system.
2026-03-03 Tue 14:20~15:20 Chin-Pao Yang Lecture Hall, R104
Shau-Yu Lan NTU
*ASIAA/NTU Joint Colloquium* Fast Quantum Gas Formation via Electromagnetically Induced Transparency Cooling
Fast Quantum Gas Formation via Electromagnetically Induced Transparency Cooling
Ultracold quantum gases play a pivotal role in many-body physics, quantum sensing, and quantum simulation. Over time, methods such as evaporative cooling in bulk ensembles and precision laser cooling techniques have been employed to achieve quantum degeneracy in atomic gases. The pursuit of a simpler, faster way to form quantum gases thus holds significant promise for advancing the field. In this talk, I will report on our creation of a quantum gas by cooling individual rubidium atoms pinned in a three-dimensional optical lattice using electromagnetically induced transparency and adiabatic expansion. After just 10 milliseconds of cooling, we verify the phase transition from a thermal to a quantum gas by adiabatically transferring the atoms into optical dipole traps. We observe the collapse of atoms in three-dimensional traps, a distinctive hallmark of a quantum gas with negative scattering length. Our results introduce a versatile and fast approach to achieving quantum degenerate gases with minimal time and resource requirements.
2026-03-04 Wed 14:20~15:20 R1203
Steve Schulze Weizmann Institute of Science
*Colloquium* Pair-Instability Supernovae in the Era of Next-Generation Surveys: Observational and Theoretical Frontiers
Pair-Instability Supernovae in the Era of Next-Generation Surveys: Observational and Theoretical Frontiers
The fate of the most massive stars remains one of the central questions in stellar evolution and time-domain astronomy. Pair-Instability Supernovae (PISNe) and Pulsational PISNe (PPISNe), the predicted endpoints of stars above roughly 95 solar masses, offer a rare opportunity to test our understanding of stellar physics and to glimpse the processes that shaped the early Universe. These explosions likely marked the deaths of Population III stars and contributed to the chemical enrichment and dust content of the first galaxies.
As facilities such as the Rubin Observatory and the Euclid, James Webb and Roman Space Telescopes begin to survey the dynamic and static high-redshift Universe (z ~ 2-10), identifying bona fide (P)PISNe becomes both crucial and increasingly challenging. Spectroscopic follow-up is limited, even for bright candidates, and several other explosion channels can mimic PISN-like signatures. This may lead to contaminated samples and biased event-rate estimates, with consequences for our broader understanding of stellar and galaxy evolution.
In this talk, I will review insights from the most promising PPISN and PISN candidates of the past decade, emphasising the key observational challenges and theoretical uncertainties that affect their interpretation. I will discuss the multi-wavelength diagnostics and observing strategies needed to identify these rare transients in forthcoming surveys. I will also outline where current progenitor and explosion models fall short, and highlight areas where theoretical progress is urgently required to interpret candidates with confidence and to anticipate the types of PISN-like events that next-generation facilities may uncover. By combining these observational lessons with pressing theoretical questions, I will outline a path towards identifying genuine (P)PISNe and constraining the physics of the most extreme stellar explosions.
2026-03-06 Fri 14:20~15:20 R1203
HyeYun Park Duke University
*Colloquium* From Hardware to Science: Commissioning and System Performance
Analysis of the Rubin Observatory
From Hardware to Science: Commissioning and System Performance
Analysis of the Rubin Observatory
Modern astronomical facilities increasingly rely on tightly integrated
hardware, software, and steady operations to deliver science-ready, high-
quality data at scale. The Vera C. Rubin Observatory represents one of the
most complex survey systems ever built, requiring comprehensive
commissioning and system-level validation to transition from construction to
science operations.
In this talk, I will present key contributions to the commissioning and early
operational phases of Rubin, with an emphasis on system performance
analysis and the interface between instrumentation, observatory
operations, and data quality. Drawing on several case studies—including
investigations of camera sensor effects, mirror vibration, and dome thermal
gradients—I will discuss how these investigations translated into
measurable improvements in image quality, stability, and survey efficiency.
Using blending and photometric redshift analyses as further examples, I will
illustrate how observatory performance connects directly to downstream
science measurements. I will conclude by discussing broader lessons from
Rubin commissioning that are relevant to survey-driven facilities and
collaborative instrumentation efforts.
2026-03-09 Mon 14:20~15:20 R1412
Shotaro Yamasaki National Chung Hsing University
*Colloquium* Fast Radio Bursts at the Dawn of a Golden Era
Fast Radio Bursts at the Dawn of a Golden Era
Fast Radio Bursts (FRBs) are millisecond-duration radio transients from cosmological distances whose physical origins remain a mystery. With recent wide-field surveys, FRB research has entered a golden era in which large, homogeneous samples now allow statistically robust tests of long-standing questions: Are most FRBs intrinsically repeating? What controls burst emission properties? And how do progenitor environments shape the observed population? In this talk, I address these questions using theory-driven statistical approaches. First, using CHIME data, I show that the observed population of apparently non-repeating FRBs is consistent with weakly repeating sources, implying a high intrinsic repeater fraction and challenging the traditional repeater/non-repeater dichotomy. Second, focusing on repeating FRBs, I present time-frequency correlation analyses that reveal systematic spectral evolution in closely spaced burst pairs, providing new constraints on FRB emission mechanisms beyond single-burst analyses. Finally, I present the first systematic study of host-galaxy metallicities for localized FRBs, demonstrating how progenitor environments can be statistically constrained and linked to population-level properties. Together, these results illustrate how the golden era of FRB observations enables a unified understanding of FRB populations, emission physics, and host-galaxy environments, and opens new paths toward their application in cosmology.
2026-03-10 Tue 14:20~15:20 R104, CCMS-New Phys. building
Tien-Ming Chuang Institute of Physics, Academia Sinica
*ASIAA/NTU Joint Colloquium* Disorder driven electronic smectic phase and charge density wave in a nonsymmorphic Sb square-net semimetal
Disorder driven electronic smectic phase and charge density wave in a nonsymmorphic Sb square-net semimetal
Electronic liquid crystal (ELC) phases are spontaneous symmetry breaking states believed to arise from strong electron correlation in quantum materials such as cuprates and iron pnictides. Here, we report a direct observation of a smectic phase in a weakly correlated non-symmorphic Sb square-net semimetal, GdSbxTe2-x. Incommensurate smectic charge modulation and intense local unidirectional nanostructure, which coexist with Dirac fermions across Fermi level, are visualized by using spectroscopic imaging-scanning tunneling microscopy. As materials with highly mobile carriers are mostly weakly correlated, the discovery of such an ELC phase are anomalous and raise questions on the origin of their emergence. Specifically, we demonstrate how chemical substitution generates these symmetry breaking phases before the system undergoes a charge density wave (CDW)-orthorhombic structural transition [1]. Furthermore, the local unidirectional nanostructures appear coupled strongly with the CDW order. We will discuss the role of disorder in comparison with the recent claim of the bond density wave in CeSbTe [2]. Together, our results highlight the importance of impurities in realizing ELC phases and present a new material platform for exploring the interplay among quenched disorder, topology and electron correlation.
1. B. Venkatesan et al., npj Quantum Materials 10, 56 (2025).
2. X. Que et al., Nature Communications 16, 3053 (2025).
2026-03-11 Wed 14:20~15:20 R1203
Ben Horowitz IPMU
*Colloquium* Connecting Scales Small and Large with Field Level Inference
Connecting Scales Small and Large with Field Level Inference
The Prime Focus Spectrograph and its Galaxy Evolution (PFS-GE) Survey mark a new era of spectroscopic programs, turning galaxy evolution into an information-rich, field-level frontier. We move from isolated measurements of individual objects and broad-stroke statistics to dense 3D maps of galaxies and their environments. The opportunity is enormous, but so is the inference challenge: the imprint of star formation, feedback, and gravitational evolution is nonlinear and entangled across scales. Much of this detail is washed away when we reduce the data to a small set of summary statistics like correlation functions.
In this talk I’ll outline an end-to-end inference paradigm that combines differentiable forward modeling with field-level reconstruction of the cosmic density field, enabling complex datasets to be translated into physical constraints with principled uncertainty propagation. I’ll discuss how this approach naturally integrates multi-wavelength multi-prove observables and systematic effects within a single framework, and how it supports direct comparisons between competing physical models. Ultimately, this shifts us from simply fitting trends to reconstructing physical histories of the evolving interplay of structure, galaxies, and baryons.
2026-03-20 Fri 14:00~15:00 R1412
Jamie Lin Tufts University
*Seminar* High redshift quiescent galaxies in overdensities at z~4-5 observed by JWST
High redshift quiescent galaxies in overdensities at z~4-5 observed by JWST
The advent of JWST has revolutionized our understanding of the early Universe, most notably through the discovery of massive quiescent galaxies (QGs) at z>4. These systems challenge standard galaxy formation models, as they require both an extremely rapid assembly of stellar mass and an abrupt cessation of star formation within the first few billion years of cosmic time. To understand the mechanisms driving this early quenching, we must investigate the role of the environment.
In this talk, I present a search for rare, high-redshift QGs within four proto-clusters in GOODS-S and GOODS-N fields at z~4-6 using JWST Cycle 1 data from the FRESCO program. Leveraging a comprehensive dataset—including up to 17 NIRCam filters, MIRI imaging, and ancillary HST data—we identify 13 QG candidates with stellar masses ranging from log(M_*/M_odot)~9-11.
Our analysis reveals a clear positive correlation between stellar mass and the quiescent fraction. Notably, we observe significant variation across proto-clusters: proto-clusters in GOODS-N exhibit a 100% quiescent fraction in the highest mass bin log(M_*/M_odot)> 10.5), while analogous structures in GOODS-S appear devoid of massive QGs. Furthermore, these galaxies reside primarily on the outskirts of overdensity peaks—contrary to z~0 expectations—and we observe a sharp decline in QG prevalence at z > 5. These findings suggest that efficient quenching mechanisms were not yet fully mature at the highest redshifts and highlight the nuanced, diverse role of environment in early galaxy evolution.
2026-03-25 Wed 14:20~15:20 R1203
Luis Ho KIAA, Peking University
*Colloquium* The Formation of Supermassive Black Holes and Galaxies at Cosmic Dawn
The Formation of Supermassive Black Holes and Galaxies at Cosmic Dawn
Supermassive black holes are ubiquitous in the nearby Universe. Their lifecycle appears to be closely connected to the evolution of galaxies. How and when did these mysterious objects form? What was the first generation of black hole seeds? How did they grow quickly enough to power the most distant quasars? And how do black holes co-evolve with galaxies? I will summarize the demographics of central black holes in the local Universe and recent discoveries made with the James Webb Space Telescope that offer surprising, new insights into the earliest phases of black hole and galaxy formation during the first billion years of cosmic history. I will outline what we know and the much else that still remains uncertain.
2026-04-01 Wed 14:20~15:20 LeCosPA auditorium
Ken Wong University of Tokyo
*Colloquium* Strong Lensing Cosmology with the New Generation of Observing Facilities
Strong Lensing Cosmology with the New Generation of Observing Facilities
Strong gravitational lensing is sensitive to the total mass
distribution along the line of sight, making it a unique probe of dark
matter in galaxies and clusters, and useful for studying resolved
properties of the magnified background sources. Strong lensing is
also valuable for constraining cosmology through lensed quasars and
supernovae (SNe), which can be monitored to measure the "time delay"
between the multiple images and constrain the Hubble constant (H_0).
This method of measuring H0 is independent of the distance ladder and
CMB observations, and may shed light on the H0 tension between early
and late-Universe measurements. The latest results from the TDCOSMO
project, including new JWST observations, constrains H_0 to be ~72
km/s/Mpc in a flat Lambda CDM cosmology with a precision of ~4.5%,
while being maximally conservative with respect to galaxy mass
profiles. As we move into the era of Rubin/LSST, new discoveries of
lensed SNe will provide complementary constraints. The
recently-discovered lensed SN "Winny" is the first galaxy-scale lensed
SNe that could be useful for time-delay cosmography. I will present
new high-resolution observations and preliminary lens models of this
exciting system. Rubin/LSST will eventually discover ~thousands of
lensed AGN and ~hundreds of lensed SNe, so finding these rare objects
in such a huge dataset is a unique challenge. I discuss
machine-learning search techniques that have been successfully applied
to the HSC SSP in preparation for LSST and other large surveys such as
Euclid and Roman. With these new observational facilities increasing
the sample of lenses by over an order of magnitude, along with the
resolving power and depth of JWST, we are poised to enter a new era of
strong lensing cosmology.
2026-04-07 Tue 14:20~15:20 Chin-Pao Yang Lecture Hall (room R104), NTU
Li-Hwai Lin ASIAA
*ASIAA/NTU Joint Colloquium* How to make galaxies green?
How to make galaxies green?
Green valley (GV) galaxies represent systems transitioning from the star-forming to the quiescent phase and thus serve as ideal laboratories for probing the physical processes that suppress or shut down star formation. In this talk, I will first provide a broader perspective on why understanding galaxy quenching is important, and then present our efforts to address key questions using a combination of state-of-the-art integral field spectroscopy (IFS) surveys and radio observations enabled by the Atacama Large Millimeter/submillimeter Array (ALMA).
*Colloquium* On the connection between observed atmospheric abundances and planetary interiors and evolutions
On the connection between observed atmospheric abundances and planetary interiors and evolutions
Exoplanet science encompasses one of the biggest existential questions: Are we alone in the universe? One promising approach to address this question is atmospheric spectroscopy, which provides a window into the composition and structure of exoplanet atmospheres. The recent launch of the James Webb Space Telescope and upcoming missions like Ariel and Twinkle provide a strong incentive for characterizing these distant worlds, with research into super-Earth and sub-Neptune exoplanets becoming increasingly popular because of their potential to reveal important clues into the origin and prevalence of life in the universe. However, the link between retrieved spectra and the underlying physical processes driving atmospheric enrichment is not well understood. Understanding these processes is crucial to interpret data and distinguish between biotic and abiotic spectral signatures. In this talk, I will explore the enrichment mechanisms leading to super-solar metallicities in super-Earth and sub-Neptune exoplanet atmospheres. The enrichment mechanisms are: (1) direct accretion of enriched nebular gas, (2) chemical processing between the planetary nucleus and the atmosphere, (3) preferential atmospheric escape, (4) geological outgassing, (5) late accretion of planetesimals, and (6) core erosion. My previous research has addressed the first three mechanisms, and my future work will explore the remaining three and identify population-level enrichment trends.
2026-04-09 Thu 14:20~15:20 R1203
Sunmyon Chon MPA
*Seminar* Emergence of overmassive BHs and LRDs in the early universe
Emergence of overmassive BHs and LRDs in the early universe
Supermassive black holes (SMBHs) are ubiquitous in the Universe, but their formation pathway remains one of the major open questions in astrophysics. One promising scenario for the origin of high-z SMBHs is the direct-collapse model. Recent JWST observations have also revealed a new population of sources, known as Little Red Dots (LRDs), at z = 4-8, which may be powered by accreting BHs.
In this seminar, I will present results from our recent cosmological radiation-hydrodynamics simulations aimed to understand the origin of luminous quasars and LRDs in the early Universe. We performed zoom-in simulations of massive halos identified by Ishiyama and Hirano (2025) as a heavy BH seed formation site. Our simulations reveal the formation of overmassive BHs that grow to several times 10^7 Msun by z ~ 7, comparable to the BH masses inferred for high-z quasars. Remarkably, seed BHs with masses of order 10^6 Msun form about 10 kpc away from the main massive halo. After their formation, a brief super-Eddington accretion phase followed by Eddington-limited growth increases the BH mass beyond 10^7 Msun. We further performed higher-resolution zoom-in simulations around these BHs and found that a very dense gaseous disk forms around them, which may broaden the emission lines. We will discuss how this system resembles LRDs and what it implies for their origin.
2026-04-21 Tue 14:20~15:20 Chin-Pao Yang Lecture Hall, R104, CCMS-New Phys. building
Pin-Jung Chiu NTU
*ASIAA/NTU Joint Colloquium* First Physics Results from JUNO
First Physics Results from JUNO
The Jiangmen Underground Neutrino Observatory (JUNO) is a 20-kiloton liquid scintillator detector located 700 meters underground in Jiangmen, Guangdong, China. Its primary physics goal is to determine the neutrino mass ordering and to precisely measure the neutrino oscillation parameters by observing fine oscillation structures in the energy spectrum of reactor antineutrinos emitted from two nearby nuclear power plants at a baseline of 53 kilometers. After approximately twelve years of construction and commissioning, JUNO began physics data-taking in August 2025. Using an initial dataset corresponding to 59.1 days of high-quality data, JUNO has reported its first physics results, including precise measurements of two oscillation parameters: sin2
2026-04-22 Wed 14:20~15:20 LeCosPA auditorium
Sunao Sugiyama Kavli IPMU
*Colloquium* Searching for Primordial Black Holes with Microlensing Data from Subaru HSC
Searching for Primordial Black Holes with Microlensing Data from Subaru HSC
Primordial black holes (PBHs) are a possible dark-matter candidate that may have formed in the early Universe from the collapse of primordial density fluctuations. If a fraction of dark matter is in the form of PBHs, they can be searched for through gravitational microlensing. To test this possibility, we have been carrying out microlensing observations of stars in the Andromeda galaxy (M31) with the Subaru Hyper Suprime-Cam (HSC). In this talk, I will present the latest results from our Subaru HSC analysis based on a new pipeline designed to improve the sensitivity of the event search. The new pipeline adopts a more flexible microlensing light-curve model, including finite-source effects, which allows improved fits to candidate events. I will also discuss the interpretation of these candidates in light of recent independent reanalyses, and conclude with the implications for future PBH searches.
2026-04-29 Wed 14:20~15:20 LeCosPA R1203 (B1F))
Kazumasa Ohno NAOJ
*Colloquium* From Exoplanet Atmospheres to Their Origins: Insights from JWST and Planet Formation Theory
From Exoplanet Atmospheres to Their Origins: Insights from JWST and Planet Formation Theory
Exoplanetary atmospheres offer clues to their formation processes and atmospheric physics and chemistry under extreme conditions. In particular, recent JWST observations have revolutionized our understanding of atmospheric compositions. In the first half of my talk, I will introduce several key findings from JWST, which include multiple molecular detections such as SO2 and metal-rich atmospheres suggested for several sub-Neptunes, including the archetypal hazy sub-Neptune GJ1214b. I will also briefly highlight my recent work on cloud and haze microphysics. In the second half, I will discuss how we can interpret the JWST atmospheric observations based on planet formation models. In particular, I will examine how atmospheric mass–metallicity relations of giant exoplanets depend on their birthplaces and gas accretion processes. I will also highlight the potential need to revisit the interpretation of atmospheric sulfur, which has conventionally been attributed to planetesimal accretion.
2026-05-06 Wed 14:20~15:20 R1203
Donghui Jeong Penn State University
*Colloquium* PoweFull.jl: Fast and Accurate code for the galaxy power spectrum including non-Gaussianity and predictions for SPHEREx
PoweFull.jl: Fast and Accurate code for the galaxy power spectrum including non-Gaussianity and predictions for SPHEREx
The upcoming generation of wide and deep galaxy surveys, such as SPHEREx and Euclid, will provide a unique opportunity to probe the ultra-large scales of structure formation, where primordial non-Gaussianity, often parameterized by f_NL, is expected to leave its most detectable imprint. At the same time, these surveys inevitably enter regimes where relativistic and wide-angle effects become significant, requiring careful modeling to extract unbiased cosmological information. We address these challenges by applying the total-angular-momentum (TAM) formalism to describe redshift-space clustering beyond the flat-sky approximation. The standard Fourier-mode description, which characterizes distortions by the angle between a mode and a line of sight, becomes ill-defined over wide fields, whereas the TAM basis naturally separates radial and angular contributions and incorporates the relevant relativistic effects. Within this framework, we provide a new parameterization of wide-angle predictions that can be compared directly with survey data. We then introduce "PowerFull", a modification of the Julia-based "2-FAST" package, which enables efficient computation of the full relativistic angular power spectrum. Finally, using Fisher information matrix–based analyses, we show that neglecting these effects biases parameter estimation, and that achieving O(1) precision on f_NL with surveys like SPHEREx requires a consistent relativistic and wide-angle treatment of galaxy clustering.
2026-05-12 Tue 14:20~15:20 Chin-Pao Yang Lecture Hall, R104
Hauyu Liu National Sun Yat-sen University
*ASIAA/NTU Joint Colloquium* The Quest for Planet Formation: Insights from Protoplanetary Disks
The Quest for Planet Formation: Insights from Protoplanetary Disks
Are we alone? You often hear this question because the formation of a terrestrial planet had been, theoretically, considered difficult if not impossible. This was changed after the NASA Kepler and K2 missions found that rocky planets are ubiquitous. Afterwards, it has become popular to resolve the natal environment of rocky planets, the protoplanetary disks, and then investigate the planet-formation activities observationally/theoretically. Without a surprise, most of those studies concluded that the protoplanetary disks we resolved are efficiently forming rocky planets, which, however, yield planets that are too wet and too carbonaceous to compare with our own Earth. Are we not alone? This is the issue I have been tackling. In this talk, I will provide an overview of this research field and outline our contribution/destruction.
2026-05-12 Tue 15:30~16:30 Chin-Pao Yang Lecture Hall, R10
Lok-Chi Chan NTU
*ASIAA/NTU Joint Colloquium* A Philosophical and Legal Reconsideration of Transparency in AI Regulation
A Philosophical and Legal Reconsideration of Transparency in AI Regulation
This paper critically examines the concept of transparency in AI systems within the domains of law and governance using tools in philosophy. Current discussions often treat transparency, explainability, and trust as closely linked, frequently requiring explainable AI (XAI) techniques as necessary justifications of AI decisions. Drawing on philosophy, cognitive science, and jurisprudence, we argue in this paper that this approach involves a category mistake: XAI explanations typically describe causal mechanisms or computational processes, which are levels below that of propositional justification expected in human deliberation, including human legal and theoretical reasoning. It concludes that transparency should be understood as a requirement in social dilbeberation rather than a purely technical feature of AI systems. Accordingly, the paper proposes a pluralistic, context-sensitive approach to AI transparency informed by analogies with existing legal and regulatory practices, with XAI serving as a useful but neither necessary nor sufficient tool.
2026-05-13 Wed 14:20~15:20 R1203
Marcel Agüeros Columbia University
*Colloquium* Low-Mass Stars in the Modern Era: Data, Models, and Surprises
Low-Mass Stars in the Modern Era: Data, Models, and Surprises
Stellar ages are notoriously difficult to measure accurately for
main-sequence low-mass stars. This limits our ability to address questions
ranging from the evolutionary state of exoplanets to the chemical history
of the Galaxy. Gyrochronology, which uses stellar rotation as a proxy for
age, is a promising solution to this quandary. Unfortunately, however, we
are still far from being able to describe fully the evolution of rotation
for low-mass stars, or from being able to use rotation measurements to
estimate accurately the ages of isolated field stars. I will summarize
recent ground-based and space-based work to characterize the rotational
behavior of G, K, and M dwarfs in open clusters ranging in age from 125
Myr (the Pleiades) to 3 Gyr (Ruprecht 147), and then compare these data to
each other and to models for stellar spin-down to appraise our current
understanding of the age-rotation relation. I will also touch on an
on-going survey targeting newly discovered single-aged stellar populations
to address the broader age-rotation-activity relation.
2026-05-14 Thu 14:20~15:20 R1203
On To Sonja Choi U. Arizona
*Colloquium* From Plans to Planets: On the Prototyping, Commissioning and
Scientific Potentials of LFAST
From Plans to Planets: On the Prototyping, Commissioning and
Scientific Potentials of LFAST
The advancement of astronomical instrumentation in the last century
has enhanced our understanding of the universe by enabling more
precise observations of new astrophysical objects. Yet, there remains
a growing need for larger apertures to achieve greater
light-collecting ability, and higher-resolution spectroscopic
measurements to resolve finer details of stars and planets. The
concept of combining light from individual telescopes, by using fused
silica fibers to create a larger effective aperture, was proposed by
Angel et al. in 1977. Building on this idea, the Large Fiber Array
Spectroscopic Telescope (LFAST) project seeks to construct large
arrays of small, individual fiber-fed telescopes to feed
high-resolution spectrographs. Our goal is to replicate a system
consisting of 20 unit telescopes, forming an array with a collecting
area comparable to that of the planned Extremely Large Telescope, at a
fraction of its cost.
2026-05-15 Fri 14:20~15:20 R1203
Yusuke Inoue Kyoto U.
*Seminar* Fate of Stripped-Envelope Massive Stars: Modeling Precursors of Interaction-Powered Supernovae
Fate of Stripped-Envelope Massive Stars: Modeling Precursors of Interaction-Powered Supernovae
Precursors of core-collapse supernovae are direct probes of the violent mass-loss episodes that massive stars undergo shortly before core collapse. While long-lasting (~10 to >70 days) precursors of hydrogen-poor supernovae (such as Type Ibn) have been observed, stellar eruption models struggle to explain these extended durations given the compact nature of their stripped-envelope progenitors. In this talk, I will propose a "shock-powered transient" scenario to resolve this discrepancy, in which the kinetic energy of erupted material is dissipated through collision with pre-existing circumstellar matter. Our multi-band light-curve model successfully reproduces the luminosities and durations of observed precursors (SNe 2006jc, 2019uo, 2021foa, and 2022pda). Combined with hydrodynamical mass-eruption simulations using MESA and CHIPS, we constrain the progenitors to be compact, hydrogen-poor massive stars with M_ZAMS ≳ 25 M_sun. Finally, I will discuss the eruption mechanisms and the core-collapse explosion process of these supernovae.
*Colloquium* Accretion-tracing line emission from gas giants: observations and theory
Accretion-tracing line emission from gas giants: observations and theory
In the last few years, photomety and spectroscopy from ground and space have opened up an exciting domain: accreting super-Jupiters, in several cases found in a gap around their parent star. This raises hopes of sharpening our understanding of processes shaping planet formation. The accretion shocks at the surface of a planet and its circumplanetary disc can be sources of hydrogen-line emission, detected at several planetary-mass accretors. Separately, if a young forming planet has a strong magnetic field, this field might channel the gas from the vicinity of the planet onto it, as for young stars. This too should lead to line emission.
We present an overview of recent (non-)detections in this rapidly-moving field and review the relevant theory. (1) We discuss how JWST can study even faint accretion tracers at planetary-mass objects. We put this in context of the not mutually exclusive accretion frameworks. (2) We present a semi-analytical model yielding line emission from the multidimensional accretion onto a planet. It reveals that accreting planets are much fainter than expected from simple formulae, which could be a major factor explaining the scarcity of detections so far. (3) We also present predictions of high-resolution profiles of hydrogen lines and their observability for different objects. We focus on Brackett alpha, accessible to the upcoming ELT/METIS (R=100,000) spectrograph.
2026-05-22 Fri 14:20~15:20 R1203
Ryosuke Kobashi ICRR
*Seminar* Time evolution of particle acceleration at supernova remnants and gamma-ray emission from clumps in the vicinity
Time evolution of particle acceleration at supernova remnants and gamma-ray emission from clumps in the vicinity
Supernova remnants (SNRs) have been considered as a source of the bulk of Galactic cosmic rays (CR). Recently, some evidence of extended gamma-ray emission have been reported by e.g. LHAASO and H.E.S.S. and this emission often has a high maximum energy, suggesting the existence of particles escaping from acceleration regions of SNRs. Although some analytical works have explained based on the escaped CR, and have calculated the gamma-ray spectrum on the environment with SNR shock interacting with clumps and have shown the spectral hardening, such works have generally not included the CR propagation. Therefore, we revisit a setup similar to the conventional CR propagation calculation, which solved the time evolution of the spatial distribution and spectrum of the accelerated particles of evolving shock and the behavior of the evolution.
In this work, we developed a simulation code that calculates the time evolution of phase-space distribution function of CR spectrum by solving the one-dimensional diffusion-convection equation coupled with analytical solutions for shock dynamics. Our results show that the total energy of accelerated particles still increases even after the age of 10kyrs in our models. We also calculated Pi0 gamma-ray emission at various stages of SNR evolution with/without clumps located at shock upstream, and compare them with several observed objects. The results show that the emission from clumps in the vicinity can dominate the total flux, depending on the distance between the shock and the clumps. To explain the observation data, the existence of clumps can play an important role.
2026-05-27 Wed 14:20~15:20 R1412
Yoichi Tamura Nagoya University
*Colloquium* LMT-FINEST: Northern Sky Exploration of High-redshift Galaxies in [O III]/[C II] with an ALMA WSU Precursor
LMT-FINEST: Northern Sky Exploration of High-redshift Galaxies in [O III]/[C II] with an ALMA WSU Precursor
A decade has passed since the first ALMA detection of [O III] 88 μm emission at the epoch of reionization (EoR), which has greatly advanced our understanding of galaxy formation up to z = 14. Also, the [CII] 158 μm line has been established as a powerful probe of neutral gas contents and star formation activities in EoR galaxies. Yet, such far-infrared nebular line studies remain largely limited to the southern sky due to ALMA's location.
We present LMT-FINEST, a new program to explore far-infrared nebular emission using FINER, an SIS mixer receiver to be deployed on the Large Millimeter Telescope (LMT) in Mexico in late 2026. Building on ALMA's Wideband Sensitivity Upgrade (WSU) technology, FINER will cover ALMA Bands 4-7 with an instantaneous frequency span of > 30 GHz per polarization, delivering Δz ~ 1 at z ~ 10 in a single tuning.
At 40% of ALMA’s light-collecting area, the LMT's similar atmospheric conditions and FINER's 5 times wider bandwidth compared to ALMA offer an unparalleled spectral scanning capability in the northern hemisphere, paving the way for efficient detection of [O III]/[C II] in galaxies identified by JWST and Euclid, and soon by Roman.
2026-06-03 Wed 14:20~15:20 R1203
Prof. Howard Chen Florida Institute of Technology
*Colloquium* Tracing the Evolution of Exoplanet Atmospheres from Birth to Maturity in Compact Systems
Tracing the Evolution of Exoplanet Atmospheres from Birth to Maturity in Compact Systems
Close-in, small exoplanets around M-dwarf stars have revealed a remarkable variety of worlds, ranging from rocky super-Earths to volatile-rich sub-Neptunes. However, understanding how these planets acquire their volatile ingredients and hold onto their atmospheres in tightly packed configurations remains a major puzzle. In compact systems, tight orbital spacing and multi-body interactions drastically alter how planets accrete volatiles, leading to atmospheric outcomes that are distinct from those in wider-orbit systems such as our own.
This talk presents preliminary efforts in understanding the atmospheric and volatile lifecycle of exoplanets in these extreme environments. The discussion will walk through three major stages of planetary evolution: i) The initial delivery and accumulation of volatiles while the planet is still forming, ii) the thermochemical evolution and mass loss from primordial gaseous envelopes, and iii) the long-term climate dynamics and chemistry that drive the emergence of secondary atmospheres and their spectral signatures.
2026-06-16 Tue 14:20~15:20 R1203
Jaime Pineda MPE
*Seminar* The Role of the Environment in Star and Disk Formation
The Role of the Environment in Star and Disk Formation
The star- and disk-formation process involves balancing gravity, turbulence, and magnetic fields. Turbulence and magnetic fields attempt to slow down the gravitational collapse. Thanks to high-angular resolution interferometric observations, much progress has been made in studying the disk properties. Unfortunately, little progress has been made in understanding the role of the environment in the formation and evolution of stars and disks.
In my talk, I will present the main results from ProPStar and PRODIGE, focusing on the connection between the physical and chemical properties of star-forming environments and the evolution of protoplanetary disks. By combining observations across different environments with modelling, these projects provide new constraints on how initial conditions shape disk structure, composition, and the material available for planet formation.
I will discuss what these results reveal about the link between environment and disk, and outline prospects for future observational and modelling efforts aimed at tracing how the earliest stages of star formation influence the emergence of planetary systems.
2026-06-18 Thu 14:00~15:00 R1203
Takuma Izumi NAOJ
*Colloquium* Multiwavelength exploration of the torus, accretion, and feedback in the Circinus galaxy
Multiwavelength exploration of the torus, accretion, and feedback in the Circinus galaxy
The Circinus galaxy hosts one of the nearest active galactic nuclei (AGN), offering a unique opportunity
to study the structure of the AGN torus, black hole accretion, and feedback processes in unprecedented detail.
In this talk, I present a comprehensive multiwavelength investigation of the Circinus nucleus, focusing on the
physical connection between cold and warm gas, accretion, and outflows. First, using high-angular-resolution
ALMA observations, we resolve the spatial distribution and kinematics of multiphase gas in the central region.
We find that molecular, atomic, and ionized gas components exhibit distinct dynamical behaviors, collectively forming
a complex, multiphase AGN torus rather than a single coherent structure. Furthermore, absorption-line observations
enable us to detect dense inflowing gas toward the AGN. The derived physical conditions indicate that gravitational instability
of the parsec-scale dense disk plays a key role in driving gas accretion from parsec scales down to the vicinity of the supermassive black hole.
Second, we present an analysis of JWST MIRI/MRS data to investigate the properties of the warm AGN torus.
In addition to directly estimating the molecular gas mass by using multiple H2 lines, we detect high-ionization
emission lines (e.g., coronal lines), which reveal fast outflows on parsec scales. By combining these results
with ALMA observations of the cold torus, we discuss the AGN torus from a truly multi-phase and multi-scale perspective,
highlighting the interplay between accretion and feedback in a nearby benchmark AGN.
2026-06-24 Wed 14:20~15:20 R1203
Zhongnan Li EACOA/KASI
*Colloquium* Understanding Circumnuclear Environments in Closest Galaxies with Multi-wavelength, High-resolution Observations
Understanding Circumnuclear Environments in Closest Galaxies with Multi-wavelength, High-resolution Observations
Galactic Circumnuclear regions, where billions of stars and putative supermassive black holes (SMBHs) interact intensely with the surrounding interstellar medium (ISM), plays a crucial role in our understanding of the feeding and feedback of SMBHs, as well as the co-evolution of the central black hole and the host galaxy. However, the direct connection between black hole feedback and the properties of the surrounding ISM remains elusive. This work makes use of multiwavelength observations to study the multiphase ISM in the circumnuclear regions of nearby galaxies (M31 and M81) in order to understand the details of this interaction. These closest galaxies provide us with a full-band, spatially-resolved view of galactic nuclei, serving as unique laboratories for understanding SMBH feedback. Through millimeter and infrared observations, it has been found that the cold gas is severely deficient in the circumnuclear region of M31 compared to that in the Milky Way. Nevertheless, the cold gas temperature is much higher than that of the galactic disk, which may be related to past nuclear activities. In addition, it is found that the nuclear region exhibits a much higher Virial parameter than the galactic disk, suggesting that the gas clump in this region is rather pressure bound or transient. The notable distinction in the molecular gas environment between the nuclear region and the disk carries significant implications (e.g., a minor mereger) for the physical conditions within this particular region. On the other hand, through optical integrated field spectroscopic observations, it is also found that there is a biconical ionized gas outflow structure located at about 200 pc from M81 center, which may be directly related to the low luminosity active galactic nucleus in M81. We use CLOUDY photoionization model to quantitatively describe the LINER radiation in the central region of both M31 and M81, and found a deficiency of [OIII] lines, indicating additional ionization sources may play a role.
2026-07-01 Wed 14:20~15:20 R1203
John Wu STScI
*Colloquium* Astronomy Re-envisioned: Investigating the Physics of Galaxy Evolution
with Machine Learning
Astronomy Re-envisioned: Investigating the Physics of Galaxy Evolution
with Machine Learning
Interpretable machine learning (ML) techniques and artificial
intelligence (AI) are revolutionizing our ability to study galaxy
evolution and large-scale structure. Convolutional neural networks
(CNNs) can now reliably predict galaxies' physical properties,
including cold gas content and metallicity, directly from three-color
optical images. These models can even reconstruct entire optical
spectra from imaging alone. Highly optimized CNNs can also robustly
identify nearby dwarf galaxies from wide-area surveys, expanding the
sample of known low-redshift satellite systems by over 10-fold.
Meanwhile, graph neural networks (GNNs) can encode simulated galaxies
amid their surroundings, learning how the galaxy–halo connection
varies with large-scale environment. These applications demonstrate
how explainable ML models with strong inductive biases enable new
scientific insights in galaxy evolution and cosmology. In the era of
wide-area galaxy surveys by the Vera C. Rubin Observatory, Nancy Grace
Roman Space Telescope, and Euclid, advanced ML and interpretable AI
methods will play an increasingly prominent role in extracting
physical understanding from astronomical datasets.
2026-07-03 Fri 14:00~15:00 R1412
Tom Bakx Chalmers University
*Seminar* When the Universe Turned Dark: Tracing Cosmic Dust from the Big Bang to Present Day
When the Universe Turned Dark: Tracing Cosmic Dust from the Big Bang to Present Day
Roughly half of all starlight ever emitted has been absorbed by interstellar dust and re-radiated at far-infrared wavelengths, fundamentally shaping our view of galaxy evolution. Even at 600 million years after the Big Bang, galaxies harbour warm dust reservoirs rivaling the brightest local systems. Yet despite the high stellar masses revealed by JWST (implying millions of dust-producing supernovae), deep ALMA observations detect no dust emission, highlighting our uncertainties in the emergence, evolution and impact of dust across the past 13.8 billion years. I will present an overview of our best constraints on early obscured galaxy evolution. Using ALMA Bands 1 through 10 efficiently, I detail our best picture on resolved dust, gas and star formation maps in 200 dusty star-forming galaxies, revealing the diversity of extreme star formation modes. Furthermore, I systematically investigate their larger environments through a novel machine learning framework, exploring the dust-selected protocluster candidates from substantial archival datasets (>2000 hours) combined with ongoing spectroscopic programs. Extending dust studies to younger galaxies, I will present a picture of dust formation and emission properties from composite ALMA imaging out to the pre-reionization Universe, concluding with recommendations for next-generation facilities (AtLAST, ALMA2040).
2026-07-08 Wed 14:20~15:20 R1203
Fred Adams University of Michigan
*Colloquium* Revisiting the Core Accretion Paradigm for Giant Planet Formation:
Analytic Framework for the Late Infall Stage and the Distribution of Planetary Masses
Revisiting the Core Accretion Paradigm for Giant Planet Formation:
Analytic Framework for the Late Infall Stage and the Distribution of Planetary Masses
This talk presents an analytic description for the late stages of giant planet formation, when planets gather the majority of their
mass. The resulting solutions show how the protoplanet properties (envelope density distribution, velocity field, column density, disk surface density, system luminosity, and emergent spectral energy distributions) vary with the input parameters of the problem
(instantaneous mass, orbital location, accretion rate, and planetary magnetic field strength). We then construct a framework for
calculating the distribution of planet masses resulting from this paradigm. In this scenario, the disk lifetime determines the end of mass accretion onto the planet. The mass accretion rate depends on the size of the Hill sphere, the fraction of the disk accretion flow that enters the sphere of influence, and the efficiency with which the planet captures the incoming material. The resulting model produces a planetary mass function with a nearly power-law form, roughly consistent with current observational estimates.
2026-07-15 Wed 14:20~15:20 R1203
Gargi Sen Indian Institute of Technology Guwahati
*Colloquium* Relativistic Accretion Flow Around Various Compact Objects & Its Astrophysical Implications
Relativistic Accretion Flow Around Various Compact Objects & Its Astrophysical Implications
Accretion onto compact objects is one of the fundamental mechanisms for powering high energy emission in quasars, active galactic nuclei, and X-ray binaries. In this talk, I will present our study of relativistic accretion flow around various compact objects and discuss its astrophysical significance. We investigate relativistic accretion flows in the strong gravity regime around compact objects by incorporating the effective potential. The infalling rotating matter may encounter a centrifugal barrier, and depending on the shock conditions, a post-shock corona (PSC) of hot, dense electrons can form. PSC reprocesses the soft disk photons to high energy radiations via inverse Comptonization. We show that shock-induced accretion flows around Kerr-Taub-NUT BHs are thermodynamically favored and yield significantly higher luminosity than shock-free solutions. BHs are not the only possible accreting compact objects, exotic compact objects like wormholes (WHs) remain theoretically viable. Therefore, we investigate the relativistic accretion flow around Kerr-like WH and show that the accretion solutions around WH can explain the observed luminosity of Cygnus X-3 in its hypersoft state. In this framework, we further examine the impact of dark matter (DM) halos on accretion dynamics, considering that the BH is surrounded by a Hernquist, Navarro-Frenk-White (NFW), Einasto, or DM spike profile. DM shifts the critical points inward and enhances disk luminosity, which offers a potential probe of DM distribution near BHs. Finally, within a steady-state GRMHD framework, we model magnetized accretion around Kerr BHs motivated by Event Horizon Telescope observations of Sagittarius A*. Our solutions reproduce magnetic field strengths within ±10% of the EHT-constrained values, that provides a consistent theoretical description of magnetized accretion flows.
2026-07-22 Wed 14:20~15:20 R1203
Misato Fukagawa Tohoku University
*Colloquium* Probing Planet-Forming Disks through Gas Dynamics
Probing Planet-Forming Disks through Gas Dynamics
Planets form in disks of gas and dust around young stars, but when and
how they emerge remains uncertain. ALMA observations have revealed that
protoplanetary disks are rich in rings, gaps, spirals, and other
substructures, especially in dust continuum emission, yet interpreting
their physical origins is challenging. In this talk, I will discuss how
observations of disk gas dynamics can provide a complementary approach
to probing the physical conditions in disks. I will focus on exoALMA, an
ALMA Large Program designed to map the three-dimensional kinematic
structure of 15 nearby protoplanetary disks at high spatial and spectral
resolution. The survey reveals widespread deviations from smooth
Keplerian disk, including large-scale spiral-like patterns and vertical
gas motions. I will present an overview of these diverse kinematic
structures, which will serve as a useful basis for future, more detailed
investigations of disk dynamics and planet formation processes.
2026-07-24 Fri 14:00~16:00 R1412
Alice Cai Northwestern University
*Seminar* Fast Radio Burst Host Galaxies with the CHIME/FRB Outriggers
Fast Radio Burst Host Galaxies with the CHIME/FRB Outriggers
Fast Radio Bursts (FRBs) are bright, millisecond pulses of radio emission of extragalactic origin, but their physical origins are still not well-understood. The Canadian Hydrogen Intensity Mapping Experiment FRB (CHIME/FRB) project has ushered in a new era of FRB science, now delivering subarcsecond-precision localizations through the addition of Outrigger stations, and their growing sample of precisely localized FRBs enables characterization of their robustly-associated host galaxies. I analyze the full sample of FRB hosts identified from both the first and second CHIME/FRB Outrigger catalogs, constructing a uniform dataset and enabling robust constraints on galaxy properties across a wide range of redshifts and environments. I place this expanded and uniformly analyzed population of hosts in the broader context of the known FRB host galaxy distribution and other transient host distributions, providing new insight into the diversity of FRB environments and their implications for progenitor models. Finally, I will discuss a second ongoing project investigating possible connections between the burst rates of repeating FRBs and their host properties.
2026-07-29 Wed 14:20~15:20 R1203
Taweewat Somboonpanyakul Chulalongkorn University
*Colloquium* CHIPS1911+4455: A Cooling flow in a Merging Cluster
CHIPS1911+4455: A Cooling flow in a Merging Cluster
The Clusters Hiding in Plain Sight (CHiPS) survey uncovered CHIPS1911+4455 at z = 0.485, a unique system that combines one of the lowest-entropy, fastest-cooling cores known with a highly disturbed X-ray morphology. At its center, the brightest cluster galaxy is undergoing a massive starburst (~150 Msun yr⁻¹), making it one of the most extreme BCGs at low redshift and a rare analog of high-z star-forming systems. I will present the discovery and characterization of this cluster with Chandra and HST, and briefly highlight recent multiwavelength follow-up, including NOEMA detections of a large molecular gas reservoir and JVLA/VLBA evidence for a newly born radio AGN. Together, these results suggest that CHIPS1911+4455 is caught in a rare transitional phase, where merger-driven turbulence and runaway cooling fuel both intense star formation and the onset of AGN feedback.
2026-08-12 Wed 14:20~15:20 R1203
Tamami Okamoto SJTU
*Colloquium* “Carbon cycle” in a protoplanetary disk
“Carbon cycle” in a protoplanetary disk
Carbon abundances in rocky planets play an important role in shaping their surface environments. Additionally, the C/O ratio in the atmospheres of gas giant exoplanets may reveal their birthplace. Therefore, it is crucial to investigate how carbon is distributed in both the gas and solid phases of protoplanetary disks. However, despite active discussion in recent years, this remains unclear due to uncertainties about the forms of carbon-bearing species in the solid phase and the motion of solids in protoplanetary disks.
In this talk, I will present the current understanding of carbon abundance and its time evolution in protoplanetary disks for both the gas and solid phases.
In the first half, I will address the unresolved problem of the solid phase: the Earth’s carbon deficit. The Earth is significantly depleted in carbon compared to comets and interstellar dust, which contain abundant refractory carbonaceous solids, such as organics and amorphous hydrocarbons. Since the disk temperature around Earth’s orbit is not high enough to vaporize these carbonaceous solids, this significant depletion remains an unsolved problem. I will discuss several models proposed to explain this deficit, focusing on thermal decomposition of organics and gasification by far-ultraviolet radiation (photolysis), as well as the limitations of these models.
In the second half, I will examine the carbon abundance in the gas phase of disks. While classical disk models only considered the sublimation of volatile carbon species such as CO and CO₂, recent studies have shown that degassing from refractory carbonaceous solids significantly contributes to the gas-phase carbon abundance. I will focus on the effects of degassing caused by photolysis and thermal decomposition of these solids.
2026-08-19 Wed 14:20~15:20 R1203
Ken Van Tilburg Stanford
*Colloquium* Intensity Interferometry for Cosmology and Fundamental Physics
Intensity Interferometry for Cosmology and Fundamental Physics
Intensity interferometry exploits temporal correlations in photon arrival times arising from the statistical properties of light to achieve angular resolution far exceeding conventional methods. Recent advances in photon-counting detectors and signal processing are enabling a new generation of intensity interferometers capable of high-precision astronomical measurements. I will present two techniques that broaden the scientific reach of this approach.
First, the expanding ejecta method (EEM) uses intensity interferometric measurements of supernovae to determine angular diameter distances from purely geometric arguments, providing a new rung on the cosmic distance ladder or enabling direct inference of the Hubble constant independent of standard candles. Second, extended-path intensity correlation (EPIC), a variant of intensity interferometry, enables differential astrometry at micro-arcsecond precision over fields of view spanning several arcseconds. One flagship
can achieve differential astrometry at micro-arcsecond precision on sources with high surface brightness over fields of view spanning several arcseconds. One flagship application is the measurement of astrometric lensing perturbations in multiply imaged quasars caused by extremely small dark matter structures. Such measurements could probe sub-stellar-mass halos, thereby providing a sensitive probe of dark matter microphysics inaccessible to other observational methods.
2026-08-26 Wed 14:20~15:20 R1203
Kazuhiro Terao SLAC
*Colloquium* Sensor-Level Foundation Models for a Data-Driven Discovery Pipeline in High Energy Physics
Sensor-Level Foundation Models for a Data-Driven Discovery Pipeline in High Energy Physics
As physicists begin to embed LLMs and agents into analysis workflows, the promise of an automated discovery pipeline is growing. Yet these pipelines still rely on "reconstruction"—the extraction of high-level physics features from raw sensor data (e.g., waveforms, images) using domain-specific tools. Because reconstruction targets a predefined set of features, it can act as an information bottleneck and introduce bias when the underlying physics model is imperfect; for simulation-trained supervised models, this appears as data shift.
We address these issues with a domain-specific Foundation Model (DSFM) that learns physics representations directly from raw, sensor-level data via self-supervised learning. The resulting representations are reusable across downstream reconstruction and analysis tasks and are free from simulation mis-modeling. I will present our sensor-level DSFM across multiple detector technologies in High Energy Physics, showing reconstruction performance competitive with or better than state-of-the-art models and up to 10,000× greater label efficiency. Finally, I show that fine-tuning can also be driven directly by data using a differentiable physics simulator.
2026-09-02 Wed 14:20~15:20 R1412
Kevin McCarthy Kavli IPMU
*Colloquium* Mocking Lyman-Break Galaxies: From UV luminosity function to growth-rate of large-scale structure
Mocking Lyman-Break Galaxies: From UV luminosity function to growth-rate of large-scale structure
Lyman-break galaxies (LBGs) are star-forming galaxies selected via the photometric "dropout" caused by the Lyman-break feature redshifting through optical passbands at z > 2, making them an efficient tracer of the high-redshift universe. The Subaru Strategic Program ʻŌnohiʻula Prime Focus Spectrograph (PFS) Galaxy Evolution Survey is about to begin its science operations, with its Tomographic sub-working group targeting LBGs at z = 2.3–3.4 to reconstruct the matter density field via the Lyman-alpha forest. In this talk, I will present a parallel effort to constrain the galaxy bias and growth-rate of large-scale structure directly from the galaxy-galaxy clustering of these same LBGs. I will focus on the construction of a realistic LBG lightcone mock, built to validate our clustering measurement and modeling pipeline and to characterize PFS-specific observational systematics. This mock-driven approach will let us deliver a robust, state-of-the-art constraint on cosmic growth-rate, fσ₈, at the highest redshifts currently probed by galaxy clustering.
2026-09-09 Wed 14:20~15:20 R1203
Yuki Inoue NCU
*Colloquium* Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS) for gravitational-wave detection
Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS) for gravitational-wave detection
We propose a next-generation international ground-based gravitational-wave detector in Taiwan, the Cryogenic sub-Hz cROss torsion-bar detector with quantum NOn-demolition Speed meter (CHRONOS), optimized for the unexplored 0.1–10 Hz frequency band between the space-based detector LISA and future ground-based detectors such as Cosmic Explorer and the Einstein Telescope. CHRONOS combines a ring-cavity Sagnac interferometer with torsion-bar test masses to realize the first quantum nondemolition (QND) measurement of angular momentum in a macroscopic system. By implementing a speed-meter readout in the rotational degree of freedom, CHRONOS coherently suppresses quantum radiation-pressure noise, enabling observations in the sub-Hz regime. We have also proposed a novel detuned power-recycling scheme to further optimize the detector sensitivity. A distinctive feature of CHRONOS is its compact design. Unlike kilometer-scale gravitational-wave observatories, the experiment can be implemented within a footprint of approximately 10 m × 10 m. This compact configuration makes it possible to develop and operate a sub-Hz gravitational-wave detector in a conventional underground laboratory while retaining sensitivity to a wide range of astrophysical, cosmological, and geophysical signals. Based on a realistic optical design incorporating torsion-bar test masses, we estimate a strain sensitivity of approximately (h ~ 1 x 10^{-18} 1/√Hz) at 2 Hz with 2.5 m arm lengths. This sensitivity enables (i) the direct detection of intermediate-mass black hole binaries, (ii) searches for stochastic gravitational-wave backgrounds, (iii) tests of Yukawa-type deviations from gravity, and (iv) searches for dark matter. Furthermore, even the 2.5 m prototype is expected to enable the prompt detection of gravity-gradient signals from earthquakes with magnitudes of approximately M5.5. CHRONOS therefore opens new opportunities for quantum-limited geophysical observations as well as multi-band and multi-messenger gravitational-wave astronomy. In this talk, we will present the current status of the CHRONOS project and recent progress in its international collaboration.
2026-09-10 Thu 10:30~11:30 R1203
Dan Jaffe GMTO
*Seminar* Giant Magellan Telescope: Status and Promise
Giant Magellan Telescope: Status and Promise
The Giant Magellan Telescope, of which ASIAA is a Founder member, is
one of two new-generation extremely large telescopes currently under
construction. It is a public-private partnership between a consortium
of 16 leading research institutions and the US National Science
Foundation. The GMT, with its innovative design and capable
instrumentation, will help us to answer key questions about the
evolution of galaxies in the early universe, the growth of
supermassive black holes and the frequency of habitable planets. I
will discuss the key science issues and how the GMT’s capabilities
address them, describe the status of the project and talk about plans
for the near-term future and about recent accomplishments.
2026-09-16 Wed 14:20~15:20 R1203
Takahiro Nishimichi Kyoto Sangyo University
*Colloquium* Dark Quest II: An emulator approach to the cosmic large-scale structures
Dark Quest II: An emulator approach to the cosmic large-scale structures
Cosmological large-scale structures are shaped by nonlinear processes mainly driven by gravity. Previous analysis methods rely on theoretical templates that are based on perturbative expansion about the linear solution, restricting the extraction of information to large, mildly nonlinear, scales. On the other hand, N-body simulations can uncover structures on smaller scales, until non-gravitational effects such as gas cooling and feedback processes eventually become a factor. However, their high computational cost hinders the direct use in statistical inference. In this talk, I will discuss the emulator approach as a potential solution. In particular, I will present our Dark Quest simulation project, especially the updated simulation code GINKAKU and the matter power spectrum emulator from the second round of the campaign. The core idea lies in the flexibility of neural network models. We show how the additional inputs to the emulator, such as the initial phases, resolution parameters, and linear power spectra, improve the predictions. I conclude by comparisons with previous emulators from independent groups, highlighting the current state of the emulator approach.
2026-10-07 Wed 14:20~15:20 R1203
Ue-Li Pen ASIAA
*Colloquium* Radio propagation from the galactic centre
Radio propagation from the galactic centre
The Sgr A* black hole is along a hyper strong scattering sightline. I present time resolved VLBA/HSA of the nearby magnetar, indicating two scattering screens: one near the earth, one half way. This places new constraints on the magnetic environment of Sgr A*, velocities in the ISM, and scattering structures. The polarization requires a third screen close to the black hole.
A novel component of this analysis for me is the extensive use of AI agents, which accelerated the analysis hundredfold. I describe the experience, and opportunities for the future.
2026-10-14 Wed 14:20~15:20 R1203
Dominik Schleicher Rome U.
*Colloquium* Little Red Dots - possible nature and origin
Little Red Dots - possible nature and origin
The James Webb Space Telescope has discovered a population of so-called "Little Red Dots" at high redshift. These are very compact astronomical sources with a red colour and a V-shaped spectrum, with the minimum located at the Balmer break. In this talk, I will review the possible interpretations of these sources, including dusty starburst galaxies, Active Galactic Nuclei and possible alternative configurations, including gas-enshrouded black holes. I will discuss the implications of the different possibilities and show how many of them imply that an active black hole is already there or in the process of formation. Subsequently, we will discuss the environments in which such sources may form. For this purpose, I will present the results of dedicated high-resolution cosmological simulations in the regime of high star formation efficiencies, a property that very likely is required to explain the shallowness of the galaxy mass function obtained with JWST. I will show how such environments very naturally produce dense and compact configurations including short migration timescales for the gas and star clusters, thereby producing a natural pathway to form a central massive black hole.
2026-10-21 Wed 14:20~15:20 R1203
Christopher Irwin Tohoku U.
*Colloquium* Transient Theory from Red to Blue
Transient Theory from Red to Blue
Modern observational surveys in optical and X-rays have continuously uncovered increasingly short-lived and faint transient phenomena, demanding advances in theory to keep pace. I will discuss recent theoretical progress on three types of events: luminous red novae associated with stellar mergers, Type II supernovae with photometry on sub-day timescales, and fast X-ray transients discovered by Einstein Probe. I will first investigate what can be gleaned about the power source of luminous red novae from their complex spectral evolution. Next, I will present a study of the puzzling red-to-blue color evolution during the early rising phase of the nearby SNe 2023ixf and 2024ggi, which indicates the presence of a steep density gradient in the immediate vicinity of their red supergiant SN progenitors. Finally, I will consider the shock breakout candidate EP 260321a recently reported by Einstein Probe and what it may reveal about the nature of Type Ib/c supernovae and their central engines.
2026-10-28 Wed 14:20~15:20 R1203
Shingo Hirano Kanagawa University
*Colloquium* Earlier and Later First Stars: Population III Star Formation Beyond the Canonical Minihalo
Earlier and Later First Stars: Population III Star Formation Beyond the Canonical Minihalo
JWST has revealed luminous galaxies and massive black holes at z > 10 that formed early and grew rapidly, while searches for signatures of Population III (Pop III) stars continue in galaxies as late as z ~ 5–10. Both lie outside the canonical minihaloes targeted by theoretical studies of first star formation. Does the Pop III initial mass function (IMF) then depend on when and where the stars form? To address this question, we have performed cosmological hydrodynamic simulations that follow Pop III star formation in a variety of environments. First, I will show how supersonic streaming motion between baryons and dark matter delays gas collapse until haloes grow more massive. These massive clouds cool rapidly during contraction, develop large filaments, and fragment into Pop III star clusters with an IMF extending to higher masses. Next, I will discuss Lyman-Werner radiation from nearby galaxies: intermediate intensities enable HD cooling and the formation of low-mass Pop III stars, whereas strong radiation leads to very massive stars and black hole seeds. Finally, I will argue that the Pop III IMF varies from halo to halo and with environment, from surviving low-mass stars to black hole seeds. I will also present ongoing simulations of haloes selected from large-scale cosmological volumes, targeting Pop III galaxy candidates at z ~ 5 and massive galaxies at z ~ 20.
2026-10-29 Thu 14:20~15:20 R1203
Takashi Hosokawa Kyoto U.
*Colloquium* Bridging Population III and Present-Day Star Formation: IMF Transition and Protostellar Heating
Bridging Population III and Present-Day Star Formation: IMF Transition and Protostellar Heating
Understanding how the stellar initial mass function (IMF) transitions from the massive-star-dominated Population III regime to present-day stellar populations remains a fundamental problem in star formation theory. The intermediate regime of very low metallicity provides a unique opportunity to investigate how gas cooling, fragmentation, and protostellar feedback shape the stellar mass distribution.
I will first present results from radiation hydrodynamic simulations of star cluster formation in turbulent, metal-poor clouds, focusing on metallicities around Z ~ 10^-3–10^-2 Z_sun. The simulations reveal how metallicity-dependent fragmentation influences the resulting IMF, including the enhanced formation of massive stars alongside numerous low-mass objects.
I will then focus on the role of protostellar radiative heating in regulating fragmentation. To explore the interplay between fragmentation during prestellar cloud collapse and its suppression by protostellar heating, we develop semi-analytic models combining one-zone thermal evolution calculations with accreting protostellar envelope structures. We find that protostellar heating suppresses fragmentation and shifts the characteristic stellar mass toward higher values at metallicities above ~10^-3 Z_sun. At lower metallicities, however, radiative heating becomes less effective at suppressing fragmentation, allowing the formation of stars with even lower masses. Meanwhile, massive-star formation is also enhanced, resulting in a stellar mass distribution extending toward both lower and higher masses.
These results highlight the distinct physical processes shaping different parts of the IMF and provide insights into the transition from primordial to present-day star formation.
2026-11-03 Tue 14:20~15:20 R1203
Sunmyon Chon Rome U.
*Colloquium* Building the First Galaxies: The IMF, Stellar Feedback, and the Birth of Star Clusters
Building the First Galaxies: The IMF, Stellar Feedback, and the Birth of Star Clusters
JWST has revealed unexpectedly abundant UV-bright galaxies and compact star clusters in the early universe, raising questions about their stellar populations and formation efficiency. I will present cosmological radiation hydrodynamic simulations that follow individual stars and their feedback from Population III star formation to the emergence of early star clusters. By connecting stellar masses to local accretion rates, we find that the IMF remains top-heavy even after metal enrichment to approximately one per cent solar. Meanwhile, radiative and supernova feedback delay subsequent star formation and keep the star formation efficiency low. I will discuss how this interplay between the IMF and feedback shapes the first galaxies and star clusters, and its implications for interpreting JWST observations.
2026-11-04 Wed 14:20~15:20 R1203
Takafumi Tsukui IPMU
*Colloquium* Insights of disk formation and evolution from JWST and ALMA
Insights of disk formation and evolution from JWST and ALMA
Most stars in the Universe form in galactic disks, making their structural and kinematical evolution central to understanding galaxy formation. Disk galaxies commonly consist of distinct thin and thick disk structures, and JWST now allows us to study these structures in distant galaxies. I will review recent observational findings showing that a present thick disk formed thin and quickly thickened, and then an additional thin disk formed within it. This transition happens in a downsizing manner (more massive galaxies proceed this evolution earlier) and the timeline is roughly aligned with the Milky Way evolution. I will discuss how these observational results corroborate the theoretical picture of galaxy evolution, including changes in halo accretion mode and gas-fraction evolution, based on the hydrodynamical simulation and ALMA observations of galaxies undergoing thick-disk formation. Finally, I will present an X-shaped bulge, the vertically evolved inner part of the bar structure, already in place at 7.6 Gyr ago, and discuss how stellar population modelling constrains when the bar underwent vertical thickening and how early disks evolved.
2026-11-11 Wed 14:20~15:20 R1203
Anirban Roy New York University
*Colloquium* Can Cosmologists Do Astrophysics with Line Intensity Mapping?
Can Cosmologists Do Astrophysics with Line Intensity Mapping?
Over the past few decades, statistical analyses of the cosmic microwave background (CMB) have established the standard model of cosmology with remarkable precision. A natural next step is to extend these statistical techniques to the integrated molecular and atomic line emission from galaxies across cosmic time. Line intensity mapping (LIM) has emerged as a powerful observational approach that enables us to study the aggregate emission from unresolved galaxies, opening a new window on galaxy formation and evolution. In this seminar, I will introduce the basic physics of molecular and atomic line emission and discuss how current and upcoming LIM experiments aim to map these signals over large cosmological volumes. I will then show how cross-correlations between LIM observations, galaxy surveys, and the 21cm signal can reveal the physical properties of galaxies and the evolution of large-scale structure. I will also discuss why LIM measurements are important for precision CMB studies, particularly on small angular scales, where molecular line emission (such as CO) can act as a significant foreground for measurements of CMB secondary anisotropies. Finally, I will present our recent detection of CO(3–2) emission from galaxies at (z~0.5), obtained by stacking Sloan Digital Sky Survey (SDSS) galaxies on CO maps reconstructed from Planck data, and discuss what this measurement demonstrates about the potential of cosmological surveys to address astrophysical questions.
asiaa.sinica.edu.tw)