投稿者: MoriyaTakashi

Supernova neutrinos in the multi-messenger era

Speaker: Shunsaku Horiuchi (Science Tokyo)

Abstract:

The historical multi-messenger firework SN 1987A confirmed the importance of neutrinos in a core-collapse supernova. However, there have been no confirmed supernova neutrino detections in the three decades since, leaving many open questions unanswered. The rise of multi-messenger astronomy opens new opportunities to detect more of these precious messengers in the future. In this talk, I will start nearby, with new prospects from a supernova in the Milky Way galaxy, before moving further in distance, to distant galaxies that power an isotropic and constant diffuse flux of neutrinos. I will highlight how these offer complementary probes of core-collapse supernovae and associated phenomena. Along the way, I will cover how the combination of theoretical, observational astronomy, and experimental neutrino communities are crucial for progress in core-collapse supernovae in the multi-messenger era. 

Connecting a Magnetized Disk to a Convective Low-mass Protostar

Speaker: Shinsuke Takasao (Musashino Art University)

Abstract:

In the early stages of star formation, boundary layer accretion—in which protostars accrete material from disks extending down to their surfaces—plays a crucial role. However, understanding how a magnetorotational-instability (MRI)-active disk connects to the protostellar surface remains a major challenge. To explore the mechanisms governing mass and angular momentum transfer, we develop a global, three-dimensional magnetohydrodynamic model of boundary layer accretion around a magnetized, convective low-mass protostar. I will present how the stellar magnetic field—coupled with stellar convection and inner disk accretion flows—strongly influences the accretion structure.

The case for a recent collision in the irregular moon system of Saturn

Speaker: Edward Ashton (ASIAA)

Abstract:

The giant planets in the Solar System all have satellites with large inclined eccentric orbits, which are known as irregular moons. Originally captured by their host planet not long after the formation of the Solar System, irregular moons are considered to be one of the most collisionally evolved minor body populations. I will talk about our recent survey of the irregular moon system of Saturn using the Canada-France-Hawaii Telescope. From observations taken between 2019 and 2023 we were able to discover 192 new irregular moons of Saturn, more than quadrupling the known number from 58 to 250. This monumental increase in the number of saturnian irregular has allowed us to see finer detail in their orbital distribution. Our most significant finding is evidence for a recent catastrophic collision within the moon system.

Characterizing sub-Neptunes around M dwarfs: recent progress and TTV opportunities

Speaker: Akihiko Fukui (U. Tokyo)

Abstract:

Sub-Neptunes are the most common class of exoplanets in close-in orbits, yet their compositions and formation pathways remain poorly understood. The Kepler space telescope revealed the radius distribution of sub-Neptunes through the transit method; however, most of these planets lack mass measurements due to the faintness and large masses of their host stars, limiting our ability to infer their internal compositions. Recently, the all-sky transit survey satellite TESS has increased the number of transiting sub-Neptunes orbiting nearby M dwarfs, i.e., stars that are both bright and low in mass, enabling more mass measurements via the radial velocity method. This method is, however, less sensitive to the masses of longer period planets, leaving the mass-radius distribution of warm and cool sub-Neptunes largely unexplored. In this talk, I will review recent progress in the observation of transiting sub-Neptunes and introduce our project to observe transit timing variations (TTVs) in multi-sub-Neptune systems using the multiband camera series MuSCAT. The TTV technique has a unique sensitivity to the masses of relatively long-period, low-mass sub-Neptunes around M dwarfs, which could offer important clues to the formation and evolution of sub-Neptunes.

Probing Demographics of Supermassive Black Holes and Host Galaxies in the Early Universe

Speaker: Masafusa Onoue (Waseda University)

Abstract:

Quasars in the distant universe are a key population for exploring the early growth history of supermassive black holes. In this talk, I will present recent JWST observations of moderate-luminosity quasars at z > 6. These quasars, originally discovered by the Hyper Suprime-Cam Subaru Strategic Program, occupy the luminosity range between the most luminous quasars and the much fainter AGN detected by JWST, thus bridging the luminosity gap. NIRCam imaging of a subset of this sample has detected stellar emission from quasar host galaxies — a feat that was not possible in the pre-JWST era due to the difficulty of detecting underlying galaxy light. Most host galaxies have stellar masses as high as ~10^10.5 solar masses. Among 12 observed, we found two galaxies that exhibit Balmer absorption lines in their NIRSpec rest-frame optical spectra — a direct signature that these accreting black holes are, to our surprise, hosted by quenching galaxies. Follow-up observations confirmed that one of these galaxies shows a clear photometric Balmer break and little excess in an H-alpha filter, confirming its quiescence. We measured the black hole–to–stellar mass ratios in this sample and found that they are not as extreme as those of more luminous quasars, which are overmassive in black hole mass by more than 1 dex. I will also present our ongoing JWST projects based on the HSC quasars, including the identification of dust-obscured broad-line quasars.

First galaxies, cosmic reionization and their interplay – successes and challenges of numerical models

Speaker: Enrico Garaldi (Kavli IPMU, U. Tokyo)

Abstract:

Within a decade, an array of observational facilities will deliver the first comprehensive picture of the reionizing Universe, from galaxies to the diffuse inter-galactic medium. Such leap forward in observational capabilities, already started with the launch of the James Webb Space Telescope, demands a comparable transformation in modeling techniques, that are currently lagging behind in accuracy. I will present ongoing efforts to build a solid theoretical framework to study this last frontier in structure formation. I will highlight current challenges in theoretical modeling and present a way forward to overcome them, to build the next state of the art in simulations of the first billion years of the Universe. Finally, I will show how new observations are enabling us to study the galaxy-IGM interplay during the tail end of reionization and place constraints on both galaxy formation and cosmic reionization models.

Secondary gravitational waves induced by primordial curvature perturbations

Speaker: Takahiro Terada (Nagoya University)

Abstract:

The direct detection of gravitational waves (GWs) marked the beginning of the era of GW and multi-messenger astronomy. In addition to astrophysical sources, we can consider the stochastic GW background as a powerful probe of the early Universe, thereby promoting the development of GW cosmology.  In this talk, I will focus on secondary GWs induced by primordial curvature perturbations, which are generated at second order in cosmological perturbation theory. These GWs carry information about small-scale primordial fluctuations that are inaccessible to cosmic microwave background and large-scale structure observations.  I will explain their physical origin and cosmological significance. For instance, such GWs can probe inflationary models—especially those predicting primordial black holes—as well as the thermal history of the Universe. I will also discuss the relevance of secondary GWs in light of recent results from pulsar timing arrays and highlight prospects for future observations.

Formation and Evolution of Filamentary Clouds Associated with High-Mass Star Formation in the Magellanic Clouds

Speaker: Kazuki Tokuda (Kagawa Univ.)

Abstract:

Recent ALMA observations have achieved ~0.1 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC), enabling the identification of filamentary molecular structures that are thought to be ubiquitous in Galactic star-forming regions. We find that the most luminous high-mass protostars (> 5 × 10^4 L_sun) in the LMC are often embedded in hub-filament systems, and some exhibit coherent, asymmetric head-tail structures extending beyond a single GMC, suggesting triggering by global-scale gas flows. In contrast, high-mass star-forming clouds in the SMC are not always filamentary. This morphological diversity may arise from thermal properties specific to the low-metallicity environment, highlighting the role of metallicity in shaping molecular cloud structures.

The Past and Future of CMB Observations

Speaker: Yuji Chinone (KEK/QUP)

Abstract:

The cosmic microwave background (CMB) radiation has been a cornerstone of modern cosmology. Over the past several decades, CMB observations have revolutionized our understanding of the universe, providing precise measurements of its age, composition, geometry, and evolution. Initial studies focused on temperature fluctuations, but more recently, measurements of linear polarization—particularly the curl-like B-mode pattern—have become central. These observations aim to uncover the smoking-gun evidence of primordial gravitational waves and probe physics beyond the Standard Model.
In this talk, I will begin with an overview of CMB observations and their applications in cosmology, highlighting key scientific milestones. I will then focus on the current and near-future landscape, with particular attention to experiments such as POLARBEAR and the Simons Observatory. I will discuss recent achievements and ongoing efforts to detect primordial B-mode polarization, constrain inflationary models, and explore new physics, including the search for axion-like particles.
Finally, I will outline the long-term vision for CMB research, including next-generation ground-based and space missions, and the role they will play in shaping the future of observational cosmology.

The search for massive stars with black-hole companions

Speaker: Soetkin Janssens (RESCEU, U. Tokyo)

Abstract:

Massive stars play an important role in the evolution of galaxies. With masses larger than eight times the mass of the Sun, these stars regulate galaxy-wide feedback and star formation. They end their lives with a violent supernova, leaving behind a compact object — neutron star of black hole. The formation of black holes is however insufficiently understood, largely due to a limited number observations. While over ten million black holes are predicted to reside in the Milky Way, only very few have been discovered so far. Moreover, in the past years, several black-hole imposters were discovered, highlighting the difficulty of the black-hole search. However, this search is far from over and the coming years may be very promising. While our current methods are very slowly becoming fruitful, a new method is on the way that may uncover hundreds of black holes at once based on astrometric data from the Gaia space telescope. This will reveal how black holes form and will help us to better understand the evolution towards gravitational wave mergers.