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天文学教室 談話会

last-update:2025/05/01

  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.

  

  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.

 

  今後の予定

5月20日(火) Jim Fuller (Caltech)

5月27日(火) Daniel Kasen (University of California, Berkeley/RESCEU)

6月3日(火) Emilie Habart (Institut d’Astrophysique Spatiale, Orsay, France)

6月10日(火) Victor Robles (Rensselaer Polytechnic Institute, USA)

 

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