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天文学教室 談話会

last-update:2026/06/18

今後の談話会

  第1842回 天文学教室談話会

2026年6月26日(金) 15:00-16:00 Koutarou Kyutoku 久徳浩太郎 (Chiba University, Japan)

Title: Gravitational-wave astrophysics with next-generation observations

Language: English

Abstract:

With the completion of Observing Run 4 by LIGO-Virgo-KAGRA, our understanding of stellar-mass compact binary coalescences has advanced considerably over the past decade. One important lesson is that, while binary neutron stars do produce r-process elements and drive short gamma-ray bursts, their mergers may not be frequent enough to account for all of these outcomes. A better understanding of physics and astrophysics surrounding binary neutron stars may require third-generation and space-borne gravitational-wave detectors. In contrast, stellar-mass binary black holes are found to be more abundant and heavier than previously thought. Relatively recently, supermassive binary black holes have also been suggested to be abundant and/or heavy by pulsar timing array observations. Detailed properties of these binary black holes are reasonably expected to be clarified further in the near future. In this talk, we will discuss future prospects of gravitational-wave astronomy and astrophysics based on our recent studies.

今後の予定

2026年7月28日(火) Ronan Kerr (The University of Toronto, Canada)

過去の談話会

  第1841回 天文学教室談話会

2026年5月26日(火) 15:45-16:45 

Title: Probing Dark Matter Physics Across Subhalo Mass Scales

Speaker: Yuka Kaneda 金田 優香 (UTokyo)

Language: Japanese

Abstract:

The Lambda-Cold Dark Matter (CDM) model has been remarkably successful in explaining the observed properties of our universe on scales larger than ~1 Mpc. However, on smaller scales, the observed properties of dark matter structures often deviate from the predictions of CDM-only structure formation. These discrepancies may be explained either by baryonic feedback processes or by alternative dark matter models motivated by particle physics, both of which can leave similar observational signatures.
To disentangle these effects, we adopt the perspective that different physical processes manifest at different dark matter subhalo mass scales. To probe the low-mass end of the dark matter subhalo population, which is directly linked to the dark matter particle mass, we develop a framework for identifying dark matter subhalos through their dynamical imprints on stellar streams. At intermediate halo masses, we show that the subhalo mass dependence of the central surface density provides a key diagnostic of both the efficiency of energy transfer from baryonic feedback to dark matter particles and the self-interaction cross-section of dark matter.
In this talk, I will discuss how scale-dependent probes of dark matter subhalos can help break the degeneracy between baryonic effects and the intrinsic properties of dark matter.

  第1840回 天文学教室談話会

2026年5月19日(火) 16:15-17:15

Title: The Most Rapidly Collapsing Molecular Clumps

Speaker: James Jackson (NRAO, USA)

Language: English

Abstract:

An analysis of the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey has produced a sample of 27 candidate dense molecular clumps with large collapse motions, as revealed by large “blue” asymmetrical line profiles of the optically thick HCO+ (1–0) line. New, more sensitive molecular line observations of this sample, conducted with the Mopra 22-m telescope, confirm the blue asymmetries in the HCO+(1–0) line profiles, with large, positive values of the asymmetry parameter A (HCO+) = 0.69±0.01, and decreasing values of A for lines with smaller optical depths, exactly as expected for collapsing clumps. The hyperfine ratios for N2H+(1–0) are in their optically thin, LTE, values, but for HCN (1–0) they are not; the F = 1 → 1 hyperfine line shows abnormally weak intensities. A simple two-component model shows that self-absorption of the background F = 1 → 1 hyperfine line by the main F = 2 → 1 hyperfine line of a cold, foreground, redshifted cloud can reproduce the observed HCN (1–0) hyperfine intensities and match both the HCN (1–0) and HCO+(1–0) line profiles. All of these results are consistent with self-absorption of the optically thick lines on the red side of the profile, as expected for collapsing clumps. This sample has large infall velocities V_inf ∼ 2.4 km s−1, the highest known, and may represent a special rapidly collapsing phase of dense clump evolution.

  第1839回 天文学教室談話会

2026年4月21日(火) 16:15-17:15 

Title: 3D Models of AGB Stars: Convection, Pulsations, and Mass-Loss Processes

Speaker: Arief Ahmad (UTokyo)

Language: English

Abstract:

Stars on the asymptotic giant branch (AGB) represent a late stage of stellar evolution during which substantial mass loss enriches the interstellar medium, yet the physical mechanisms driving this process remain only partially understood. In particular, the interplay between pulsations, convection, and dust formation produces complex and time dependent behaviour that challenges simplified modelling approaches. Global three dimensional radiation hydrodynamics simulations, such as those computed with CO5BOLD, provide a framework in which convection and pulsations arise self consistently from the stellar interior, allowing these processes to be studied from first principles. In this seminar, I will present how such models provide physical insight into the origin and characterisation of pulsations, and discuss how their interaction with convection shapes the structure and variability of AGB atmospheres, ultimately enabling dust formation and mass loss through massive stellar winds.

  第1838回 天文学教室談話会

2026年4月16日(木) 15:00-16:00

Title: The long-term evolution of turbulent discs in high-redshift galaxies

Speaker: Joss Bland-Hawthorn (University of Sydney, Australia)

Language: English

Abstract:

Most disc galaxies go through an early epoch of being “gas rich,” an era that is being actively explored today through ALMA and JWST observations. This high gas-fraction phase got going much sooner (z > 3) than anticipated by cosmological N-body simulations. A new class of controlled (Nexus) simulations of these early times reveals that these turbulent discs have extraordinary properties. Unexpectedly, m=2,3 spiral arms, stellar and gaseous bars, even X-shaped/peanut bulges, all form under these conditions. The high gas content accelerates stellar migration and stabilizes the disc against buckling. Moreover, baryon sloshing driven by strong feedback gives rise to thick stellar discs, a likely origin of alpha-enriched thick stellar discs observed today. The sloshing gives rise to specific signatures that may already be observable in ALMA data. We discuss the implications of the new work on galaxy studies.

  第1837回 天文学教室談話会

2026年4月14日(火) 16:15-17:15

Title: Photon Counting CMOS Imaging Detectors for Optical and UV Astrophysics

Speaker: Don Figer (Rochester Institute of Technology, USA)

Language: English

Abstract:

NASA’s Habitable World Observatory (HWO) will observe faint sources in ultralow (photon-per-hour) backgrounds. In this talk, we present NASA-funded research to advance single-photon counting and radiation-tolerant CMOS detectors for NASA missions, in particular, those requiring optical/UV photon counting detectors. In the project, we will measure the performance of Fairchild Imaging large-format single photon counting and photon number resolving CMOS imaging detectors (HWK4123) before and after radiation that simulates the environment at L2. These detectors have very low capacitance sense nodes to produce a large voltage response to a single photon. In a predecessor project, we found that performance for a similar detector (QIS, Gigajot Technologies) is little-changed after exposure to 50 krad(Si). The dark current can be set to beginning-of-life levels with modest additional cooling, 4–6 K for an 11-year mission. The project seeks to minimize the transient and long-term effects of radiation in NASA missions and also to design a single photon counting and photon number resolving NIR detector with similar architecture.

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