Schedule for 2025
| April |
10 |
Shu-ichiro Inutsuka (Nagoya U.) |
|
17 |
Hiroshi Kobayashi (Nagoya U.) |
|
24 |
Kanta Kitajima (Nagoya U.) |
| May |
8 |
Tomotaka Nishikawa (Nagoya U.) |
|
15 |
Yuji Miko (Nagoya U.) |
|
22 |
Kota Kobayashi (Nagoya U.) |
|
29 |
TBD |
| June |
12 |
Hayato Shimizu (Nagoya U.) |
|
19 |
Shusuke Utsumi (Nagoya U.) |
| July |
17 |
Rehearsal of presentations for the summer school by M1 students |
Previous Talks
| Date/Room |
April 10, 14:00 @ES606 |
| Speaker |
Shu-ichiro Inutsuka (Nagoya U.)
|
| Title |
Star Formation and Evolution of Milky Way Galaxy |
Abstract |
I will briefly summarize the recent progress in our understanding of ISM dynamics and Star Formation and try to envision the future development of the research in our group. The latter includes the evolution of disk galaxies, halo-disk connection, star cluster formation with many binaries, and planet formation. But the choice of actual subjects explained in the talk may depend on the number of questions and available time of three hours!
|
| Date/Room |
April 17, 14:00 @ES606 & zoom |
| Speaker |
Hiroshi Kobayashi (Nagoya U.)
|
| Title |
Theory of Planet Formation |
Abstract |
The origin of gas giant planets, such as Jupiter and Saturn, is discussed along the core-accretion scenario, in which gas giants are formed via rapid gas accretion onto massive solid cores. However, the formation of massive cores includes a lot of difficulties. I review the difficulty of core formation via planetesimal or pebble accretion. I show the possible scenario for core formation based on dust-to-planet simulations.
The collisional outcome is important for planet formation. I drive a nice outcome model based on collisional simulations, which may allow us to understand collisional outcomes in various scales from dust to planets.
|
| Date/Room |
April 24, 14:00 @ES606 |
| Speaker |
Kanta Kitajima (Nagoya U.)
|
| Title |
Particle-Based Analysis of Relativistic Jets |
Abstract |
In this presentation, we will analyze a simulation of a stationary high-temperature gas accelerating to a relativistic velocity. The Special Relativistic Godunov Smoothed Particle Hydrodynamics (SRGSPH) [Kitajima+ 2025, submitted] will be employed to model the fluid as a collection of discrete particles, known as SPH particles, and to describe the fluid's motion through the interaction of each SPH particle with its environment. By leveraging the advantages of the SPH method, we can investigate fluids in vacuum regions, which have traditionally been challenging to address with standard numerical methods. This study takes advantage of the unique aspects of the SPH method to simulate a jet from a high-temperature source into a vacuum and analyze its acceleration mechanism. The findings from this analysis provide valuable insights into the driving mechanisms of relativistic jets, including those observed in active galactic nuclei and gamma-ray bursts.
|
| Date/Room |
May 8, 14:00 @ES606 & zoom |
| Speaker |
Tomotaka Nishikawa (Nagoya U.)
|
| Title |
Observational prediction of gamma-ray emission from knee-energy cosmic rays accelerated by core-collapse supernovae |
Abstract |
Galactic cosmic rays (CRs) are commonly thought to undergo acceleration through diffusive shock acceleration (DSA) mechanism within supernova remnants (SNRs). Recent observations of SNRs with ages ~10^2 - 10^3 yrs indicate that the maximum energy of cosmic rays does not reach ~PeV level. Recently, Inoue et al. 2021 demonstrated through kinetic-MHD simulations that cosmic rays gain high energy up to 3 PeV when a blast wave shock propagates through a dense circumstellar medium (CSM) within tens of days after the explosion. In their model, the dense CSM is assumed to be created by a stellar wind of a red supergiant (RSG) with a mass-loss-rate of 10^-3 M_Sun yr^-1, which is supported by recent observations of supernovae. To prove PeV accelerations, observations of 100 TeV gamma-rays, which are generated by PeV CRs via neutral pion decay, can be effective. However, these hadronic gamma-rays from a very young SNR can be hardly attenuated by interactions with soft photons from the supernova photosphere and cosmic background radiations. Previous studies argued that it is very hard to detect these gamma-rays if we assume a CSM formed by conventional RSG wind with ~10^-5 M_Sun yr^-1. In this study, using the kinetic-MHD simulations data by Inoue et al. 2021, we calculate the gamma-ray flux emitted from a blast wave shock propagating in the dense CSM by considering the environmental attenuations. We find that we can expect considerably larger gamma-ray flux than that reported in the previous studies, if we assume the modern mass-loss-rate wind of ~10^-3 M_Sun yr^-1. We predict that the Cherenkov Telescope Array can detect 100 TeV gamma-rays even by 50 hours integration if a type II SN happens in nearby galaxies within 4.8 Mpc. Based on the observed star formation rates, we can expect such an event once per 10 years.
|
| Date/Room |
May 15, 14:00 @ES606 & zoom |
| Speaker |
Yuji Miko (Nagoya U.)
|
| Title |
隕石の惑星大気進入による気流・熱状態への影響のモデリング |
Abstract |
若い地球型惑星には頻繁に隕石が衝突し、その大気の進化には衝突過程が大きな影響を及ぼす。隕石衝突前の惑星大気は、地表からの熱により、地表付近の対流圏と上層の成層圏が存在する。しかし、隕石衝突により高温・高圧領域が発生、膨張することで、大気の流れや熱状態が大きく乱される。この流れは非常に複雑であり、流体シミュレーションにより調べる必要がある。
本研究ではAthena++を用いて、大気に突入する隕石が及ぼす影響について3次元流体シミュレーションを行った。大きな隕石の場合、地表に衝突し、エネルギーを解放することで爆発現象のような膨張が発生する。一方、小さな隕石の場合、大気中で破壊され、上空でエネルギー解放が起こる。また、隕石の軌道上に生じる煙突状の希薄領域も重要である。そこで、エネルギー解放領域と煙突状の希薄領域に分けて隕石の影響のモデル化を行った。そして、背景大気の初期条件として、下層に対流圏、上層に成層圏が存在している大気を用意し、以上のモデリングのもとシミュレーションを行った。その結果、エネルギー解放による膨張波が希薄領域で早く伝わることで、爆発領域付近の下層大気がはるか上層にまで運ばれることを確認した。
次に、本研究のシミュレーション結果を実際の隕石落下事例と比較した。2013年2月15日に小天体Chelyabinskが衝突したイベントは多くの観測がなされており、衝突体の大きさ、密度、進入角度など多くのデータがある。これらのデータと我々のモデルをもとに数値計算を行い、地表での圧力を求めた。本研究のシミュレーションの結果と実際の被害から推測される圧力分布を比較した結果、実際の被害分布を再現可能であり、モデルの妥当性が確かめられた。また、大気中での隕石の破壊に伴うエネルギー解放領域の形状に制限を与えることもできた。
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