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.

 

  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.

 

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.

 

  今後の予定

7月8日(火) Patricio Sanhueza (Department of Astronomy, U. Tokyo)

7月15日(火) Ryuta Orihara (Department of Astronomy, U. Tokyo)

7月22日(火) Chinami Kato (Department of Physics, U. Tokyo)

11月11日(火) Patrick Francois (Observatoire de Paris, France)

11月18日(火) Masahiro Machida (Kyushu University)

11月25日(火) Alessio Traficante (INAF-IAPS, Italy)

  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

• • 2024年度
  • 2023年度
  • 2022年度
  • 2021年度
  • 2020年度
  • 2019年度
  • 2018年度
  • 2017年度
  • 2016年度
  • 2015年度