MENU

天文学教室 談話会

last-update:2026/01/21

今後の談話会

  第1835回 天文学教室談話会

2025年3月10日(火)

Title: TBD

Speaker: Yuki Isobe 磯部優樹 (UK)

Language: 

Abstract:

今後の予定

—

過去の談話会

  第1834回 天文学教室談話会

2025年1月20日(火) 15:00-16:00

Title: Probing the Universe with Fast Radio Bursts

Speaker: Xavier Prochaska (UC Santa Cruz, USA/Kavli IPMU)

Language: English

Abstract:

I will highlight recent results leveraging well-localized fast radio bursts (FRBs) to study cosmology and galaxy formation in our universe.  The fundamental signals inherent in FRBs – dispersion measure (DM), rotation measure (RM), and fluence – offer unique constraints on properties of the matter along the sightline to Earth.  In turn, we may map out the cosmic web, constrain the density of gas surrounding galaxies, and infer the magnetic fields of the interstellar medium from a diverse population of galaxies.  I will describe the standard observational and analysis techniques and conclude by emphasizing areas poised for tremendous growth in the next few years due to the ongoing or upcoming commissioning of new facilities and systems (e.g. CRACO on ASKAP, DSA+, and the CHIME Outriggers project).

  第1833回 天文学教室談話会

2025年1月6日(火) 15:30-16:30

Title: Dust Characterization in Protoplanetary Disks with High-Resolution Multi-wavelength ALMA Observations

Speaker: Kiyoaki Doi 土井聖明 (Max Planck Institute for Astronomy, Germany)

Language: Japanese 日本語

Abstract:

Planets form through the growth and accumulation of dust in protoplanetary disks. However, the process from dust to planetesimals remains not fully understood. Observational characterization of the dust in protoplanetary disks provides key constraints on this process. Recent high-resolution ALMA observations have spatially resolved the dust emission and revealed substructures such as rings and gaps. The spatial distribution of dust is an important indicator of dust accumulation and potential sites of planet formation. Also, multi-wavelength observations can reveal dust properties such as grain size and surface density, which are key indicators of dust growth and the masses of possible planets.
In this talk, I will present our high-resolution ALMA studies of PDS 70 and HD 163296. Our Band 3 observations of PDS 70 reveal the radial and azimuthal dust distribution and provide a picture of dust accumulation outside the already formed planets. Our detailed analysis of a high-resolution image of HD 163296 reveals the vertical dust distribution, which is an indicator of dust growth and concentration as well as the disk environment. Also, we performed spectral analysis including Band 9 observations as a temperature tracer and estimated dust size and surface density. Overall, high-resolution, multi-wavelength observations are a powerful approach for constraining disk properties, which are key to understanding the process from dust to planets.

  第1832回 天文学教室談話会

2025年12月23日(火) 15:40-16:40

Title: JWST spatially resolved mappings reveal molecular chemistry under strong Far-UV irradiation in the planetary nebula NGC 6302

Speaker: Mikako Matsuura 松浦美香子 (Cardiff University, UK)

Language: English

Abstract: Planetary nebulae (PNe) serve as excellent laboratories for studying the physics and chemistry of photoionized and photon-dissociated regions (PDRs), which are shaped by intense UV radiation. They also provide insights into dust grain formation, processes relevant to star-forming regions and protoplanetary disks. A key advantage of PNe is their large spatial extent, allowing for detailed observation with modern telescopes like the JWST.

We present JWST spectral mapping of the planetary nebula NGC 6302, one of the most extreme PNe, characterized by a bipolar morphology, fast outflows, and an extremely hot central star (~220,000 K). NGC 6302 is a prototype of mixed chemistry, exhibiting both oxygen- and carbon-based compounds, including silicate and polycyclic aromatic hydrocarbon (PAH) dust.
JWST detected PAHs, as well as CH3+, the key ingredient to trigger ionised molecular chemistry. The stratification of H+, H2 and PAHs in NGC 6302 differs from what is observed in a typical PDR (photo-dissociation region), the Orion Bar. One of the possible explanations is that the formation timescale of PAHs is longer than that of H2, capturing the site of PAH formation on the disk and the outflow.

  第1831回 天文学教室談話会

2025年12月17日(水) 16:00-17:00

Title: Future Flagship to Revolutionize Astronomy: The Habitable Worlds Observatory

Speaker: Chris Packham (Univ. Texas, San Antonio, USA)

Language: English

Abstract: The coming decades will afford the chance to transform our knowledge of the universe and perhaps will reveal compelling evidence of life outside of the Earth.  In this presentation I explore the facilities that will enable such advances, advancing the successes of the JWST and 8m ground based telescopes.  Uniquely achieved through multi-national collaborations, leveraging the technical and scientific skills of those partners, as well as spreading the costs and risks, a revolutionary scientific future beckons.

  第1830回 天文学教室談話会

2025年12月16日(火) 15:45-16:45

Title: Illuminating the Thermodynamics of Protoplanetary Disks

Speaker: Shangjia Zhang (Columbia University, USA)

Language: English

Abstract: For most of their lifetime, protoplanetary disks are primarily heated by their central stars. The resulting thermal structure determines disk’s vertical density structure, and has been extensively modeled both theoretically and observationally. Recently, however, I found that how a disk is illuminated also influences its dynamics. The vertical shear instability, for instance, is sensitive to thermal stratification. Many observed disks show shadows cast by misaligned inner disks, producing asymmetric thermal structure. Such asymmetries can drive spirals, open gaps and rings, generate vortices, excite eccentricity, and induce warps, depending on the detailed illumination geometry. Thus, illumination is not only a radiative transfer problem, but also highly intertwined with hydrodynamics, affecting long term disk evolution. This theory is uniquely testable: by modelling thermal structure from disk observations, one can directly predict its corresponding kinematics, which can be confirmed in ALMA line observations.

  第1829回 天文学教室談話会

2025年12月9日(火) 16:15-17:15

Title: Revealing dynamic history and structure of the Milky Way

Speaker: Natsuki Funakoshi 舩越 菜月 (University College London, UK)

Language: English

Abstract: 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.

  第1828回 天文学教室談話会

2025年12月4日(木) 15:30-16:30

Title: Transition-metal-driven heterogeneous astrocatalysis in the interstellar medium

Speaker: Gerard Pareras Niell (Universitat Autònoma de Barcelona)

Language: English

Abstract: Can industrial-style heterogeneous catalysis operate in the interstellar medium? Transition metals (TMs) are key players in terrestrial catalysis: their ability to coordinate a variety of ligands and activate otherwise inert molecules underpins processes such as Fischer–Tropsch (H₂ + CO) and Haber–Bosch (H₂ + N₂). In these systems, metallic surfaces act as heterogeneous catalysts that adsorb and transform reactant molecules. In astrochemistry, icy mantles on dust grains are often invoked as catalytic media, but their ability to open multiple, low-barrier reaction channels is limited compared to TM sites. Here we show that interstellar dust grains incorporating transition metals such as iron (Fe) and nickel (Ni) can display catalytic properties closely resembling terrestrial heterogeneous catalysts. Using density functional theory (DFT) simulations combined with kinetic modelling, we investigate Fischer–Tropsch-type chemistry on Fe-based catalytic sites under interstellar conditions. We consider supported single atoms and nanoclusters on silica (SiO₂) and silicon carbide (SiC), as well as mineral grains such as troilite (FeS). We find that the conversion of CO and H₂ into alcohols (e.g. methanol and ethanol), ketene, methane, and short hydrocarbon chains (ethene, ethane) is feasible within realistic temperature ranges, and that adsorption energies at TM sites are sufficient to retain key reactants. These results establish heterogeneous astrocatalysis by transition metals as a viable pathway for complex molecule formation, opening new synthetic routes for chemical and potentially prebiotic evolution in space.

  第1827回 天文学教室談話会

2025年12月3日(水) 14:00-15:00

Title: The Origin of Supermassive Black Holes from Pop III.1 Seeds and Implications for Particle Physics and Cosmology

Speaker: Jonathan C. Tan (Chalmers / U. Virginia)

Language: English

Abstract: The origin of supermassive black holes (SMBHs) is a key open question for contemporary astrophysics and cosmology. Here we discuss the predictions of a model of SMBH formation from Pop III.1 protostars, i.e., metal-free stars forming in locally isolated dark matter minihalos, where dark matter annihilation has a chance to alter the structure of the star allowing growth to supermassive scales (Banik, Tan & Monaco 2019; Singh, Monaco & Tan 2023; Cammelli et al. 2025; Nandal et al. 2025; Sanati et al. 2025a,b; for a review see Tan et al. 2024 and this project page: http://cosmicorigins.space/smbh). The model predicts that all SMBHs form very early in the Universe (i.e., by z ~ 20) with a spatial distribution that is initially relatively unclustered. It also makes predictions for SMBH occupation fractions, host galaxy properties, frequency of binary SMBHs and the gravitational wave background. These predictions are compared to latest results from the Hubble Space Telescope, James Webb Spact Telescope and pulsar timing array observations. Another key prediction of the model is an early phase of “flash” ionization of the universe at z~20, which can help alleviate cosmological tensions (Hubble tension, dynamical dark energy, negative neutrino masses) (Tan 2025; Komatsu & Tan 2025). Finally, since the Pop III.1 mechanism relies on the process of WIMP dark matter self-annihilation, there are implication for the nature of the dark matter particle.

  第1826回 天文学教室談話会

2025年11月25日(火) 16:15-17:15

Title: The star formation mechanisms from a Galaxy-wide point of view

Speaker: Alessio Traficante (INAF-IAPS, Italy)

Language: English

Abstract: The formation mechanism of stars, particularly the most massive ones, remains a fundamental open question in astrophysics. Several competing theories have emerged in recent years, each aiming to explain the multi-scale nature of star formation: how parsec-scale clumps arise within their parent molecular clouds (tens of parsecs in size), and how these clumps fragment down to core scales of a few thousands of AU, the progenitor of the final cluster of stars. A major challenge in resolving this process lies in disentangling the various contributions from gravity, turbulence and feedback, which all act combined in yet unpredictable ways at the various scales.

In this seminar, I will present recent results that shed light on these mechanisms across multiple spatial scales. At parsec scales, the interplay between gravity and turbulence is explored through molecular line surveys and FIR/submm continuum data, particularly from the MALT90 and Hi-GAL surveys respectively. At smaller scales, the recently released ALMAGAL project now allows, for the first time on a Galaxy-wide basis, an investigation of gas dynamics and fragmentation in nearly 1000 dense clumps. I will review key findings from ALMAGAL and discuss how the physical properties of clumps relate to those of their embedded cores.
Finally, to fully interpret these complex datasets, direct comparison with numerical simulations is essential. To this end, we have developed the Rosetta Stone project, an end-to-end framework that begins with magneto-hydrodynamical simulations of star-forming regions, processes them through a dedicated post-processing pipeline, and generates synthetic observations that closely replicate real data. This approach enables a comprehensive and physically consistent comparison between simulations and observations, opening up the way toward a deeper understanding of the star formation process.
I will conclude the seminar with the future perspectives: a new ALMA Large Project, called “Panta Rei”, will shed light on the interplay between turbulence and gravity in a statistically significant way across the Galaxy; finally, future radio surveys with MeerKAT and SKA will contribute to a complete understanding of the role of feedback in the interplay with gravity and turbulence.

  第1825回 天文学教室談話会

2025年11月18日(火) 16:15-17:15

Title: Star Formation Simulations from a Prestellar Core to the Class II Disk Stage

Speaker: Masahiro Machida 町田 正博 (Kyushu University 九州大学)

Language: English

Abstract: Recent ALMA observations have revealed detailed structures in star forming regions, including protostellar outflows, jets, asymmetric gas accretion, and rotationally supported disks. Ring and gap substructures, which are signatures of planet formation, have also been detected even during the gas accretion phase of star formation. We performed magnetohydrodynamic simulations of star formation starting from a prestellar core and followed the formation and evolution of a protostar and its surrounding disk. The simulations reproduced the emergence of outflows and jets, as well as circumstellar disks with complex morphologies, envelopes, and asymmetric accretion flows. Comparison with ALMA data helps clarify the physical picture of the early stages of star formation. In this talk, I will discuss recent progress in understanding the early phase of star and disk formation revealed through both simulations and observations.

  第1824回 天文学教室談話会

2025年11月11日(火) 16:15-17:15

Title: Detailed abundances of CEMP stars

Speaker: Patrick Francois (Observatoire de Paris, France)

Language: English

Abstract: The first low resolution spectroscopic HK  and  Hamburg-ESO  (HES) surveys have permitted the discovery of numerous metal-poor stars. (EMP stars, VMP stars). Among them, a fraction of EMP stars has revealed  the presence of a high enhancement of C. These stars are now known as   Carbon Enhanced Metal Poor Stars (CEMP).The high resolution spectroscopic  abundance analysis of these CEMP stars has shown that they can be classified in several groups depending on their  s-process and r-process  relative abundances. I will review the characteristics of these different groups of CEMP stars from the most recent studies and the current understanding on their origin and their link to the early galactic chemical history.

  第1823回 天文学教室談話会

2025年11月4日(火) 16:15-17:15

Title: The Role of Gas in Star Cluster Formation

Speaker: Jeremy Karam (Department of Astronomy, U. Tokyo)

Language: EnglishAbstract: Star cluster formation takes place embedded inside giant clouds of molecular gas scattered throughout galaxies. The embedded nature of this process makes observing young clusters challenging, forcing us to turn to simulations. However, computational constraints can leave simulating massive cluster formation incomplete due to resolution limitations which often prevent us from being able to simulate each individual star alongside the entire gas reservoir. We perform zoom-in simulations of star cluster assembly inside a gas-rich molecular cloud.  We resolve star cluster formation at a resolution that allows us to follow each individual star alongside the gas reservoir it evolves within. We consider the dynamical evolution of the cluster as it merges with smaller clusters inside the molecular cloud, and compare these dynamics to those found from Gaia observations of young clusters in the Milky Way. With these simulations, we find that the morphology of the surrounding gas plays a vital role in cluster evolution, and can control the dynamical evolution of the cluster even after the cluster has left its embedded phase. We also introduce a new method to use observations as initial conditions for star cluster formation that will allow for the most realistic star cluster formation simulations to date.

  第1822回 天文学教室談話会

2025年10月30日(木) 15:00-16:00

Title: Non-thermal Coronal Magnetic Activity in Nearby Seyferts

Speaker: Yoshiyuki Inoue 井上 芳幸 (Osaka University 大阪大学)

Language: English

Abstract: Central supermassive black holes of active galactic nuclei (AGNs) host hot plasma with an electron temperature of 10^9 K, namely coronae. Like the Sun, black hole coronae are theoretically believed to be heated by their magnetic activity. However, such magnetic activity has not been observed yet. In this talk, I will report recent studies on coronal magnetic activity in nearby AGNs using ALMA. The estimated coronal magnetic fields are typically ~10-100 G on scales of ~10-100 Schwarzschild radii. The measured magnetic field is weaker than the theoretical expectation, requiring a new corona heating mechanism. I will also discuss particle acceleration processes in the coronae of Seyferts, which might be the production sites of the high energy neutrinos recently seen by IceCube.

  第1821回 天文学教室談話会

2025年10月28日(火) 16:15-17:15

Title: Magnetic field structure of neutron stars in accreting X-ray binaries

Speaker: Kinjal Roy (Raman Research Institute, India)

Language: English

Abstract: An X-ray binary(XRB) is a binary system consisting of an accreting neutron star(NS), white dwarf or black hole and a main sequence companion star.  High-mass X-ray binaries (HMXB) are a subclass of X-ray binaries with the companion mass greater than ten solar mass. A compact star produces X-ray radiation during the accretion of material from the stellar wind or Roche lobe overflow. High-mass X-ray binaries are ideal places to stellar winds, material exchange between binary stars, and the  evolution of magnetic field strength of the NS. In this talk I will present the study of cyclotron lines present in a couple of transient HMXBs namely 4U 0115+63 and Cep X-4. I will discuss how the cyclotron line energies vary with source luminosity and check them against the predictions from theoretical models.

  第1820回 天文学教室談話会

2025年10月21日(火) 16:15-17:15

Title: Polarized news from ALMA: Magnetic fields in nearby star forming cores (BOPS and ALPPS)

Speaker: Josep Miquel Girart (Institut de Ciències de l’Espai & Institut d’Estudis Espacials de Catalunya, Spain)

Language: English

Abstract: The relevance of the magnetic fields at core scales (<0.1pc) during the protostellar phase has not well been established yet. One one hand, there are some regions that show the expected hourglass magnetic field, suggesting that neither angular momentum, nor turbulence is strong enough to perturbe significantly the field, and only gravity does it. On the other hand, there are other protostellar regions that show a significantly perturbed magnetic field. In order to address this issue statistically, we present to studies, BOPS and ALPPS, based on linear polarization of the dust observed with ALMA at 345 GHz. BOPS and ALPPS explore the magnetic fields at envelope scales (few hundred to few thousand au) in a total of 60 and 38 protostars, respectively. In this talk, I will give an update of the status of these two projects.

  第1819回 天文学教室談話会

2025年10月14日(火) 15:00-16:00

Title: Tidal Evolution with Internal Gravity Waves

Speaker: Linhao Ma (KITP at UC Santa Barbara, USA)

Language: English

Abstract: Internal gravity waves (IGWs) exist in radiative zones inside a star, and when tidally excited by a nearby companion, they could cause efficient tidal dissipation with radiative damping, shaping the spin and orbital evolution of the system. In this talk, I will talk about their effects in different kinds of astrophysical systems. For a Wolf-Rayet-black-hole binary, tidally excited IGWs may efficiently transfer the orbital angular momentum to the Wolf-Rayet star, which may collapse to a fast-rotating black hole at the end of its lifetime. For binaries containing a sub-dwarf B (sdB) star, these waves may help them to achieve tidal synchronization, which can be directly compared to asteroseismic observations of sdBs. For main-sequence stars with a close-in planet, IGWs may trigger resonance locking, causing steady orbital migration of the planet, and the orbital distribution of these planets will hence depend on the properties of their host stars.

  第1818回 天文学教室談話会

2025年10月7日(火) 15:00-16:00

Title: Latest XRISM Insights into the Explosion Asymmetry and Ejecta Composition of Cassiopeia A

Speaker: Manan Agarwal (University of Amsterdam, Netherlands)

Language: English

Abstract: Cassiopeia A (Cas A) is the youngest known core-collapse supernova remnant in the Milky Way, offering a unique laboratory for studying nucleosynthesis products of massive star explosions, their velocity distribution soon after the explosion, and interaction with the surrounding environment. With the launch of XRISM and its high-resolution X-ray spectrometer, Resolve, new spatially resolved observations of Cas A have revealed unprecedented details in elemental abundances, their dynamics, and plasma properties. In this talk, I present the latest XRISM results from two bright regions in the remnant—the southeast and northwest—which highlight several asymmetries in the remnant that are crucial to understand explosion mechanisms. Our detailed Bayesian-based spectral analysis reveals key new insights — the incomplete shell structure of the stellar ejecta with varying dynamic properties, discovery of intriguing low velocity, narrow lines near Cas A’s projected, and the first detection of odd-Z elements P, Cl, and K in the X-ray band. These results highlight the power of XRISM in mapping the dynamics and chemical structure of supernova remnants.

  第1817回 天文学教室談話会

2025年7月22日(火) 15:30-16:30

Title: Neutrino Flavor Physics in Supernova

Speaker: Chinami Kato 加藤ちなみ (Department of Physics, U. Tokyo)

Language: Japanese

Abstract: It is well established that neutrinos play an essential role in driving core-collapse supernova explosions. Neutrinos exist in six flavors, each contributing differently to the dynamics of the explosion. With the recent advancement of neutrino detection technologies, a variety of detectors—sensitive to different neutrino flavors—have been developed or are currently being planned. This progress necessitates the development of theoretical models that can accurately describe neutrinos of all flavors. One of the most significant uncertainties in current supernova modeling arises from collective neutrino oscillations. These are nonlinear flavor conversions induced by neutrino-neutrino self-interactions, particularly in regions close to the proto-neutron star where the neutrino density is extremely high. Due to their inherent nonlinearity and fine structure in phase space, collective oscillations present a major challenge for numerical modeling and require sophisticated approaches to understand their impact on both the explosion mechanism and observable neutrino signals. In this presentation, I will provide an overview of recent progress in the study of collective neutrino oscillations in the context of core-collapse supernovae, with a particular focus on my own research addressing nonlinear flavor evolution in high-density environments.

  第1816回 天文学教室談話会

2025年7月15日(火) 15:30-16:30

Title: Probing the Innermost Regions of Protoplanetary Disks through Non-Axisymmetric Shadows Analysis

Speaker: Ryuta Orihara 折原龍太 (Department of Astronomy, U. Tokyo)

Language: Japanese

Abstract: A comprehensive understanding of planet formation is essential for uncovering our origins. A pivotal component of this process is the protoplanetary disk, which forms around nascent stars and serves as a natural laboratory for studying planet formation. Recent advances in observational techniques have enabled the accumulation of extensive data on the early stages of planetary system development. However, terrestrial planets like Earth are believed to form in the innermost regions of protoplanetary disks, typically within just a few au of their central star. Direct imaging of these regions remains highly challenging due to the limited spatial resolution of current telescopes. To address this limitation, two primary approaches have been proposed: enhancing spatial resolution through techniques such as sparse modeling and machine learning, and extracting physical information from indirect disk features. This study focuses on the second approach to probing inner disk structures. We propose a novel method to estimate the three-dimensional geometry of the innermost regions of protoplanetary disks by analyzing non-axisymmetric shadows cast onto the outer disk in scattered light images. We further explore the potential of this technique to improve our understanding of planet formation by offering new constraints on inner disk dynamics and structure.

  第1815回 天文学教室談話会

2025年7月8日(火) 15:45-16:45

Title: Magnetic Fields in High-mass Star Formation

Speaker: Patricio Sanhueza (Department of Astronomy, U. Tokyo)

Language: English

Abstract: The importance of the magnetic field in the formation process of stars is a long-standing question. Here, we introduce the first ALMA survey, Magnetic Fields in Massive Star-forming Regions (MagMaR), aiming to understand the role of the magnetic field in high-mass star-forming regions. In MagMaR, 30 fields have been observed with ALMA at 1.2 mm, resulting in ~0.3″ resolution (~1000 au). A large variety of magnetic field morphologies is detected: (1) “simple” spiral- or hourglass-like, that are dominated by a single, bright continuum source; (2) filamentary, with magnetic field vectors sometimes parallel to the elongated dust emission and characterized with aligned fragmentation; (3) complex magnetic field morphology with highly clustered fragmentation. We have succeeded modeling the field of a couple “simple” fields, which, together with case studies from the survey, point to the magnetic field playing only a minor energetic role when compared to other energies in play. The first analysis of the whole star-forming core sample confirms this point. We find statistical evidence that the core elongation exhibits a preferentially more parallel alignment with magnetic fields at 1000 au scales, in agreement with our MHD simulations with initially super-Alfvenic (turbulence dominates magnetic fields) conditions. We offer compelling statistical evidence that the formation of cores is governed by turbulence rather than magnetic fields in the context of clustered massive star formation, contradicting the prediction of classical magnetically regulated models.

  第1814回 天文学教室談話会

2025年7月1日(火) 16:15-17:15

Title: Testing Hubble Tension Systematics with Cepheids, TRGB & JAGB

Speaker: Li Siyang (John Hopkins University, USA)

Language: English

Abstract: The Hubble Tension refers to a >5 σ discrepancy between local and cosmological measurements of the Hubble constant (H0) and suggests the possibility of undiscovered early-universe physics or underestimated systematics. Probing the Hubble Tension necessitates intense scrutiny of the Cepheid-based distance scale, which currently provides the strongest constraints on local measurements of H0. One powerful approach to crosscheck systematics in the Hubble Space Telescope (HST) Cepheid section of the distance ladder is to develop and improve independent routes to measure distances to the same set of galaxies and H0, such as those using the tip of the red giant branch (TRGB) and J-region asymptotic giant branch (JAGB), or by adding an independent anchor. I will present a sub-2% Cepheid distance to M31, which prepares an additional anchor galaxy that can be used to construct the distance ladder once a high-precision geometric detached eclipsing binary observation is feasible, as well as work improving standardization and calibration of the TRGB, including a 2D maximum likelihood formalism enabling Milky Way field star calibrations and contrast ratio standardization in the maser host NGC 4258. I will also present recent James Webb Space Telescope (JWST) TRGB distances to 8 hosts of 10 Type Ia supernovae (SNe Ia), later expanded to 25 hosts, which provides no evidence of a HST Cepheid systematic resolving the Hubble Tension, in addition to a H0 measurement using JWST observations of the JAGB with an expansion to 15 galaxies hosting 18 SNe Ia. While the JAGB remains promising as a tool that can crosscheck Cepheid systematics, non-uniform asymmetry in its luminosity function, caused in part by stellar contamination, presently limits the precision of this candle.

  第1813回 天文学教室談話会

2025年6月10日(火) 16:15-17:15

Title: A Quantum-like perspective for the dark matter: Implications in our nearby Universe

Speaker: Victor Robles (Rensselaer Polytechnic Institute, USA)

Language: English

Abstract: Satellite abundance in Milky Way-like halos plays a crucial role in distinguishing dark matter models, in particular, in dark matter models where a suppression of substructure is expected below a mass scale. One model that has gained recent interest is the Quantum/Fuzzy or Wave Dark Matter model, where the dark matter is assumed to be very small (~10-22-10-21eV/c2), this model predicts a sharp suppression of small-scale structures. Capturing the intrinsic quantum field inference has been numerically challenging with current codes. I will show that with the new implemented fluid-wave hybrid scheme in the code GAMER-2 code, we have achieved a self-consistent Wave Dark Matter cosmological simulation of a Milky Way-size halo with a dark Matter particle mass of m=2×10-23eV, which simultaneously resolves the solitonic core of the host halo and captures the complex tidal evolution of subhaloes down to z=0. In this talk, I will discuss the implications of the wave dark matter in dwarf mass halos in isolation and the evolution of Wave DM subhalos inside a MW-mass host. I will mention some consequences on the current and future constraints to the quantum-like hypothesis from observations of the satellite abundance and dynamical mass content of nearby dwarf galaxies.

  第1812回 天文学教室談話会

2025年6月3日(火) 16:15-17:15

Title: FUV-irradiated molecular clouds and proto-planetary disks as seen by JWST

Speaker: Emilie Habart (Institut d’Astrophysique Spatiale, Orsay, France)

Language: English

Abstract: Nearby Photo-Dissociation Regions (PDRs) in the two giant Orion molecular clouds has been successfully observed in imaging and spectroscopy as part of the JWST ERS program PDRs4All (https://pdrs4all.org/) and GTO 1192. This allows to study with great precision at small spatial scales the effects of FUV radiative feedback from massive stars on interstellar molecular clouds and proto-planetary disks. This presentation overviews the observations and the dominant physical and chemical processes that lead to the infrared emission that JWST will detect in many environments. I will discuss how FUV radiation influence the physical structure, dust evolution, chemistry, dynamics and how it is connected. Robust diagnostics to constrain the gas and
grain properties will be highlighted, as well as,  the importance of still little-used microphysical/chemical processes such as the excitation of molecular hydrogen, with direct consequences on the water and carbon chemistry.

  第1811回 天文学教室談話会

2025年5月27日(火) 16:15-17:15

Title: Supernova Explosions and Their Aftermath

Speaker: Daniel Kasen (University of California, Berkeley/RESCEU)

Language: English

Abstract: Understanding how massive stars die in core-collapse supernova explosions  is a long standing challenge, with simulations struggling to reproduce successful explosions and fully capture the diversity of observed events. Recent advances in 3D multi-physics simulations are now finding success and shedding light on how stellar properties and environments influence explosion dynamics, the formation of neutron stars and black holes, and the nucleosynthesis of heavy elements. At the same time, observations are revealing surprising phenomena—supernovae with extreme luminosities or unusual X-ray and radio behavior—pointing to ongoing energy input from the central engine well after the initial blast. I will highlight recent developments in supernova modeling, which now track the entire sequence from explosion onset and stellar disruption through to the observable signatures in light curves and spectra. The convergence of simulations and observations is offering a more complete understanding of how massive stars end their lives—and what they leave behind.

  第1810回 天文学教室談話会

2025年5月20日(火) 16:15-17:15

Title: Tumultuous lives of massive binary stars

Speaker: Jim Fuller (Caltech)

Language: English

Abstract: Massive binary stars create exotic supernovae, energetic gamma-ray bursts, merging black holes, and other high-energy phenomena that are affected by processes that occur during the progenitor star’s evolution. For instance, helium stars spun up by tidal forces can produce highly spinning black holes that may be observed in LIGO data or via gamma-ray bursts. I will discuss our current understanding of angular momentum transport in stars, and expectations for black hole spins. I will also discuss new calculations of tidal spin-up in massive helium stars that predict low spins in most cases. In supernova progenitor stars with a close binary companion, mass transfer can accelerate enormously at the end of the star’s life, creating very dense circumstellar material observed in type IIn and Ibn supernovae. Finally, new simulations of stable mass transfer measure the amount of angular momentum lost during this process, with key implications for orbital contraction and the formation of gravitational wave sources.

  第1809回 天文学教室談話会

2025年5月13日(火) 16:15-17:15

Title: Probing dark matter with resonant dynamics of the Galactic bar

Speaker: Rimpei Chiba 千葉凛平 (Department of Astronomy 天文学教室)

Language: English

Galactic bars are elongated, rotating structures observed in more than two thirds of disk galaxies, including our own Milky Way. In the presence of dark matter in our Universe, these bars are predicted to gradually spin down by gravitationally transferring their energy and angular momentum to dark matter, a process known as dynamical friction. In contrast, modified gravity theories predict no bar slowdown, suggesting that the spin-down of galactic bars is a key indication of the existence of dark matter. I will present the first implication for this deceleration of the galactic bar in the Milky Way from the kinematics and chemistry of stars trapped in resonance with the bar: just like tree rings, the resonantly trapped phase-space evolves inside-out, capturing new stars by expanding its surface as it sweeps towards larger angular momentum, while conserving the internal distribution. Using the recent data from the Gaia satellite, I will show that the bar’s corotation resonance bears this tree-ring structure, allowing us to infer the bar’s evolutionary history.

  第1808回 天文学教室談話会

2025年4月22日(火) 16:15-17:15

Title: Planet formation scenarios with observational constraints

Speaker: Satoshi Ohashi 大橋聡史 (Department of Astronomy 天文学教室)

Language: Japanese 日本語

Planet formation has been investigated with great attention for long because this question is related to the origin of our life. Coagulation of dust grains in a circum-stellar disk has been studied as one of the most reliable processes to form planets since Hayashi 1980. However, recent ALMA observations have been revealing a variety of structures in disks, which were not previously considered. In this talk, I will review the basic ideas of several methods to form planets especially focused on the coagulation process and compare those with observations. Then I will focus on the future prospects with on-going projects such as ng-VLA and SKA.

  第1807回 天文学教室談話会

2025年4月15日(火) 16:15-17:15

Title: The Role of Protostellar Variability in Stellar Mass Assembly

Speaker: Gregory Herczeg (KIAA/Peking University)

Language: English

Young stellar objects are notoriously variable. The largest amplitudes are seen on FU Ori objects, bursts of a factor of ∼1000 in accretion rate that may last for centuries. However, the importance of such large bursts in stellar assembly remains uncertain. In this talk, I will discuss the role that variability plays at the different stages of evolution of young stellar objects and consequences for planet formation. I will highlight the JCMT Transient Program, the first dedicated sub-mm monitoring program, to measure the role of bursts in the earliest stages of stellar assembly, and will discuss future prospects for protostellar monitoring.

  第1806回 天文学教室談話会

2025年4月8日(火) 15:00-16:00

Title: Tidal Disruption Events and Their Radio Flares

Speaker: Tatsuya Matsumoto 松本達矢 (Department of Astronomy 天文学教室)

Language: Japanese 日本語

Most galaxies harbor a supermassive black hole (BH) at their center. When a star approaches too close to the BH, it is destroyed by a strong tidal force of the BH. Such tidal disruption events (TDEs) have been discovered by wide field surveys in optical and X-rays. In the former part of this talk, I will review the basics of TDEs and their observational status. In the latter part, I will talk about my recent studies focusing on radio flares accompanying TDEs.

 

  天文学教育研究センター談話会について

天文学教育研究センター談話会については、こちらをご覧ください。

  本郷キャンパスでの天文・宇宙物理関係のセミナーアナウンスについて

東大本郷キャンパスの天文・宇宙物理関連のセミナーをアナウンスする際は、
hongo-astrotalks (at-sign) astron.s.u-tokyo.ac.jp
をお使いください。 このアドレスにメールを出すと、以下のグループの構成員に展開されます。

  • 天文学教室
  • RESCEU
  • 物理学教室
    • 安東研究室
    • 宇宙理論研究室
    • 日下研究室
    • 馬場研究室
    • 山本研究室

幅広い関係者にメールが展開されることに留意して、多くの人が興味を 持ちそうなセミナー・教室談話会などのアナウンスにお使いください。

 

  過去の談話会