イベント検索
70 件
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セミナー
Exploring material strengths of dust aggregates in planet formation by numerical simulations
2023年12月8日(金) 14:00 - 15:15
辰馬 未沙子 (理化学研究所 数理創造プログラム (iTHEMS) 研究員)
The planet formation process is the growth from sub-micrometer-sized cosmic dust grains to thousand-kilometer-sized planets. This growth process has broadly two phases: the growth from dust grains to kilometer-sized planetesimals, mainly driven by intermolecular forces like van der Waals forces and hydrogen bonds, and the subsequent growth from planetesimals to planets, governed by gravitational forces. However, the planetesimal formation process encounters various challenges, including fragmentation and bouncing resulting from collisions among dust aggregates. To gain insights into the planetesimal formation process and how to avoid these obstacles, I have been focused on measuring and formulating the material strengths of dust aggregates using grain simulations. In this talk, I will introduce my works on the material strengths of dust aggregates and their applications to kilometer-sized bodies in the solar system, such as comets and asteroids.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語
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セミナー
Early Formation of Dark Matter Halos
2023年11月24日(金) 14:00 - 15:15
デリック・ビーティー・インマン (理化学研究所 数理創造プログラム (iTHEMS) 研究員)
Cosmological observations have led to an extremely precise understanding of the large-scale structure of the Universe. A common assumption is to extrapolate large-scale properties to smaller scales; however, whether this is correct or not is unknown and many well-motivated early Universe scenarios predict substantially different structure formation histories. In this seminar I will discuss two scenarios where nonlinear structures form much earlier than is typically assumed. In the first case, the initial fluctuations are enhanced on small scales leading to either primordial black holes clusters or WIMP minihalos right after matter-radiation equality. In the second, I will show that an additional attractive dark force leads to structure formation even in the radiation dominated Universe. I will furthermore discuss possible observations of such early structure formation including changes to the cosmic microwave background, dark matter annihilation, and when the first galaxies form.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語
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セミナー
Neutrino production in AGN cores: Constraints from Kinetic Plasma Simulations
2023年10月6日(金) 14:00 - 15:15
Amir Levinson (Professor, Tel Aviv University, Israel)
Accreting black holes power a variety of high-energy astrophysical systems. The activation and mode of operation of these engines has been subject of intensive research. In recent years the structure of the multi-flow emanating from the putative, giant black hole in the M87 galaxy was probed down to near horizon scales in unprecedented detail, shedding new light on the physics of accretion and the processes responsible for the formation and dissipation of relativistic jets by the black hole. I shall review recent progress in observational and theoretical studies of accreting black hole engines.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語
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セミナー
Progenitors and Explosion Properties of Supernova Remnants Hosting Central Compact Objects
2023年10月6日(金) 10:00 - 11:30
チェルシー・ブラウン (Ph.D. Student, Department of Physics and Astronomy, University of Manitoba, Canada)
Presented is a systematic, global study of Galactic supernova remnants (SNRs) hosting Central Compact Objects (CCOs) aimed at addressing their explosion properties and supernova progenitors. With the Chandra and XMM-Newton telescopes, a spatially resolved X-ray spectroscopy study is performed on seven SNRs that show evidence of shock-heated ejecta. Using an algorithm, we segmented each SNR in the sample into regions of similar surface brightness. These regions were fit with one- or two-component plasma shock model(s) in order to separate the forward-shocked interstellar medium from the reverse shock-heated ejecta which peak in the X-ray bands for elements including O, Ne, Mg, Si, S, Ar, Ca, and Fe. We subsequently derived the explosion properties for each SNR in the sample and found overall low explosion energies (<10^51 erg). To address their progenitor mass, we compare the measured abundances from our spectroscopic modelling to five of the most widely used explosion models and a relatively new electron-capture supernova model. Additionally, we explore degeneracy in the explosion energy and its effects on the progenitor mass estimates. However, no explosion models match all of the measured ejecta abundances for any of the SNRs in our sample. Therefore, we present our best progenitor mass estimates and find overall low progenitor masses (<=25 solar masses) and we highlight the discrepancies between the observed data and the theoretical explosion models.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Collective Plasma Effects in Relativistic Radiation-Mediated Blast Waves
2023年9月8日(金) 14:00 - 15:15
Arno Vanthieghem (Princeton-NINS Postdoctoral Research Fellow, Department of Astrophysical Sciences, Princeton University, USA)
Relativistic radiation-mediated shocks (RRMS) dictate the early emission in numerous transient sources such as supernovae, low luminosity gamma-ray bursts, binary neutron star mergers, and tidal disruption events. These shock waves are mediated by Compton scattering and copious electron-positron pair creation. It has been pointed out that a high pair multiplicity inside the shock transition leads to a lepton-baryon velocity separation, prone to plasma instabilities. The interaction of the different species with this radiation-mediated microturbulence can lead to coupling and heating that is unaccounted for by current single-fluid models. Here, we present a theoretical analysis of the hierarchy of plasma microinstabilities growing in an electron-ion plasma loaded with pairs and subject to a radiation force. Our results are validated by particle-in-cell simulations that probe the nonlinear regime of the instabilities and the lepton-baryon coupling in the microturbulent electromagnetic field. Based on this analysis, we derive a reduced transport equation for the particles that demonstrates anomalous coupling of the species and heating in a Joule-like process by the joined contributions of the decelerating turbulence, radiation force, and electrostatic field. We will then discuss the effect of finite magnetization on the general dynamics and recent efforts toward a more self-consistent description of the coupling. In general, our results suggest that radiation-mediated microturbulence could have important consequences for the radiative signatures of RRMS.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Evidence against a strong first-order phase transition in neutron star cores: impact of new data
2023年8月1日(火) 13:30 - 15:00
Len Brandes (Ph.D. Student, Technical University of Munich, Germany)
Information on the phase structure of strongly interacting matter at high baryon densities can be gained from observations of neutron stars and their detailed analysis. Bayesian inference methods are used to set constraints on the speed of sound in the interior of neutron stars, based on recent multimessenger data in combination with low-density constraints based on chiral effective field theory and perturbative QCD constraints at asymptotically high densities. A detailed re-analysis is performed in order to clarify the influence of the latter constraints on the inference procedure. The impact of the recent new heavy (2.35 M_sol) black widow pulsar PSR J0952-0607 and of the unusually light supernova remnant HESS J1731-347 is inspected. One of the consequences of including PSR J0952-0607 in the database is a further stiffening of the equation-of-state, resulting in a 2.1 solar-mass neutron star in a reduced central density of less than five times the equilibrium density of normal nuclear matter. A systematic Bayes factor assessment quantifies the evidence (or non-evidence) for small sound speeds, necessary for a strong first-order phase transition, within the range of densities realized in the core of neutron stars. Given the presently existing database, it can be concluded that the occurrence of a strong first-order phase transition in the core of even a 2.1 solar-mass neutron star is unlikely, while a continuous crossover cannot be ruled out.
会場: via Zoom (メイン会場) / セミナー室 (132号室)
イベント公式言語: 英語
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セミナー
A dynamical model for IRAS 00500+6713: the remant of a type Iax supernova SN1181 hosting a double degenerate merger product WD J005311
2023年7月7日(金) 14:00 - 15:15
黄 天鋭 (東京大学 ビッグバン宇宙国際センター (RESCEU) 博士課程)
Iras 00500+6713 is a bright nebula in the infrared, and X-ray observations show it consists of diffuse region and strong illuminated central region. In addition, optical spectral observations have recently revealed that fast wind with about 15,000 km/s is blowing from the massive white dwarf at the center. The properties of this nebula and white dwarf are very similar to those theoretically predicted by the binary white dwarf merger. In addition, its position on the celestial sphere and the extent make it a prime candidate for the remnant of SN 1181, a historical supernova. In this study, we propose that such a multilayered structure is formed by the collision between the remnant of SN 1181 and the stellar wind blowing from the central white dwarf, and succeeded in constructing a model that is consistent with the multi-wavelength observations. The results show that the progenitor of SN 1181 is a binary white dwarf with 1.3-1.9 solar mass and that their merger triggered an explosion that ejected mass with 0.2-0.6 solar mass to form the present object. The extent of the X-ray source concentrated in the center reveals that these winds began blowing within the last 30 years, and we will discuss this property as well.
会場: セミナー室 (359号室) / via Zoom
イベント公式言語: 英語
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セミナー
Quantum uncertainty of fields and its effect on entanglement generation in quantum particles
2023年5月31日(水) 14:00 - 15:15
杉山 祐紀 (九州大学 大学院理学府 物理学専攻 博士課程)
The unification of gravity and quantum mechanics is one of the important problems. To elucidate the theory of quantum gravity, it is becoming more and more important to get any hint of the quantum nature of gravity. In particular, the quantum-gravity-induced-entanglement of masses (QGEM) scenario, which is expected to observe the quantum nature of non-relativistic gravity, has recently attracted great attention. In this talk, we show the effect of relativistic fields on entanglement generation based on quantum field theory. We also discuss the relationship between the entanglement generation and quantum uncertainty of the fields.
会場: セミナー室 (359号室) / via Zoom
イベント公式言語: 英語
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セミナー
X-ray study on the synchrotron emission in Kepler's SNR
2023年5月19日(金) 14:00 - 15:15
Vincenzo Sapienza (東京大学 大学院理学系研究科 物理学専攻 博士課程)
Synchrotron X-ray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high energy electrons accelerated at the shock front. We performed a spatially resolved spectral analysis of the young Kepler's SNR, where we identify two different regimes of particle acceleration. In the north, where the shock interacts with a dense circumstellar medium (CSM), we found a more efficient acceleration than in the south, where the shock velocity is higher and there are no signs of shock interaction with dense CSM. We also studied the temporal evolution of the synchrotron flux, from 2006 to 2014. A number of regions show a steady synchrotron flux and equal cooling and acceleration times. However, we found some regions where we measured a significant decrease in flux from 2006 to 2014. Our results display a coherent picture of the different regimes of electron acceleration observed in Kepler's SNR. Also If I will have time during the seminar it will be nice to present also some preliminary results I will have in the SN 1987A project.
会場: セミナー室 (359号室) / via Zoom
イベント公式言語: 英語
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セミナー
Towards EeV Neutrino Astronomy with GRAND
2023年4月18日(火) 14:00 - 15:15
クミコ・コテラ (Director of Research, Institute of Astrophysics, France)
We are living exciting times: we are now able to probe the most violent events of the Universe with diverse messengers (cosmic rays, neutrinos, photons and gravitational waves). One challenge to complete the multi-messenger picture resides in the highest energies, as no ultra-high energy neutrinos have been observed yet. This challenge could be undertaken by the GRAND (Giant Radio Array for Neutrino Detection) project, which aims at detecting ultra-high energy particles, with a colossal array of 200'000 antennas over 200'000 km2, split into ~20 sub-arrays of ~10'000 km2 deployed worldwide. In this talk, we will present preliminary designs and simulation results, plans for the ongoing, staged approach to construction, and the rich research program made possible by the proposed sensitivity and angular resolution.
会場: コモンルーム (246-248号室) / via Zoom
イベント公式言語: 英語
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セミナー
Cosmic magnetism and its effects on the observed properties of ultra high-energy cosmic rays
2023年3月10日(金) 14:00 - 15:00
Ellis Owen (大阪大学 大学院理学研究科 宇宙地球科学専攻 宇宙進化グループ JSPS特別研究員)
Ultra high-energy (UHE) cosmic rays (CRs) from distant sources interact with intergalactic radiation fields, leading to their spallation and attenuation through photo-hadronic processes. Their deflection and diffusion in large scale intergalactic magnetic fields (IGMFs), in particular those associated with Mpc-scale structures, alter the cumulative cooling and interactions of a CR ensemble to modify their spectral shape and composition observed on Earth. In this talk, I will demonstrate the extent to which IGMFs can affect observed UHE CRs, and show that source population models are degenerate with IGMF properties. Interpretation of observations, including the endorsement or rejection of any particular UHE CR source classes, needs careful consideration of the structural properties and evolution of IGMFs. Future observations providing tighter constraints on IGMF properties will significantly improve confidence in assessing UHE CR sources and their intrinsic CR production properties.
会場: via Zoom / コモンルーム (246-248号室)
イベント公式言語: 英語
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セミナー
Understanding kilonova spectra and identification of r-process elements
2023年1月20日(金) 14:00 - 15:00
土本 菜々恵 (東北大学 大学院理学研究科 天文学専攻 博士課程（学術振興会特別研究員）)
Binary neutron star (NS) merger is a promising site for the rapid neutron capture nucleosynthesis (r-process). The radioactive decay of newly synthesized elements powers electromagnetic radiation, as called kilonova. The detection of gravitational wave from a NS merger GW170817 and the observation of the associated kilonova AT2017gfo have provided with us the evidence that r-process happens in the NS merger. However, the abundance pattern synthesized in this event, which is important to understand the origin of the r-process elements, is not yet clear. In this talk, I will first introduce an overview and current understanding of kilonova. Then, I will discuss our recent findings of elemental features in photospheric spectra of kilonova toward identification of elements.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Mergers of neutron star-neutron star (or black hole) binaries as r-process sites
2023年1月13日(金) 14:00 - 15:00
和南城 伸也 (Senior Scientist, Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Germany)
The discovery of an electromagnetic counterpart (kilonova) associated with GW170817 confirms that binary neutron star (NS) mergers are at least one of sites of r-process nucleosynthesis. However, there is no observational evidence that black hole (BH)-NS mergers are r-process sites. In this talk, we overview the latest work of nucleosynthesis based on long-term hydrodynamics simulations of NS-NS and BH-NS mergers covering early dynamical and late post-merger mass ejections. We also briefly discuss a possible constraint on nuclear equations of state.
会場: via Zoom / コモンルーム (246-248号室)
イベント公式言語: 英語
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セミナー
Modelling Optical Signals from Magnetar-Driven Supernovae
2022年12月20日(火) 14:00 - 15:00
Conor Omand (Postdoctoral Researcher, Department of Astronomy, Stockholm University, Sweden)
Many energetic supernovae are thought to be powered by the rotational energy of a highly-magnetized, rapidly-rotating neutron star. The emission from the associated luminous pulsar wind nebula (PWN) can affect the system in different ways, including accelerating the ejecta, ionizing the ejecta, and breaking the spherical symmetry through hydrodynamic instabilities or large scale asymmetries. Modeling the observables from these processes; the light curves, spectrum, and polarization; is essential from understanding the nature of the central engine. I will present the results of a radiative transfer study looking at the effects of a PWN on the supernova nebular spectrum, and the preliminary results from a more physically motivated light curve model for parameter inference, and a study examining the polarization that arises due to hydrodynamic instabilities in the ejecta of engine-driven supernovae.
会場: コモンルーム (246-248号室) / via Zoom
イベント公式言語: 英語
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セミナー
Quantum kinetics of neutrinos in high-energy astrophysical phenomena
2022年12月9日(金) 14:00 - 15:00
長倉 洋樹 (国立天文台 科学研究部 特任助教（国立天文台フェロー）)
Neutrinos are the most mysterious and elusive particles in the standard model of particle physics. They play important roles in core-collapse supernovae and binary neutron star mergers as driving mass-ejection, synthesizing heavy elements including r-process nuclei, and neutrino signals from these sources. This exhibits the importance of accurate modeling of neutrino radiation field in these phenomena, which will be used to connect neutrino physics to multi-messenger astronomy. It has recently been suggested that neutrino-flavor conversion (or neutrino-oscillation) can ubiquitously occur in these astrophysical environments, exhibiting the requirement of quantum kinetic treatments in the modeling of neutrino transport. In this seminar, I will give an overview of the quantum kinetics neutrino transport and then introduce its recent progress, paying a special attention to the connection to astrophysics. I will also present the latest results of our numerical simulations of collective neutrino oscillations, which can be properly accounted for only by quantum kinetic framework.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Energy partition in Weibel-mediated shock waves: from Supernova Remnants to Gamma-Ray Bursts
2022年11月24日(木) 14:00 - 15:00
Arno Vanthieghem (Princeton-NINS Postdoctoral Research Fellow, Department of Astrophysical Sciences, Princeton University, USA)
Gamma-ray bursts and supernovae provide ideal environments for efficient energy channeling between different plasma species through collective processes such as collisionless shock waves. Extensively studied in astrophysical and laboratory environments, observations and kinetic simulations indicate strong electron heating in the precursor of collisionless shock waves propagating in unmagnetized electron-ion plasmas. We outline a theoretical model accounting for electron heating via a Joule-like process through the interplay between pitch-angle scattering in the microturbulence and the coherent electrostatic field induced by the difference in inertia between species. Using analytical kinetic estimates, semi-analytical Monte Carlo methods, and ab-initio Particle-In-Cell simulations, we demonstrate the validity of this model in the relativistic regime relevant to the afterglow emission of gamma-ray burst and extend it to characterize the electron-to-ion-temperature ratio in the downstream of nonrelativistic high-Mach numbers shock waves relevant for supernova remnants and laboratory experiments.
会場: via Zoom
イベント公式言語: 英語
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セミナー
UHECR anisotropy: effects of the Galactic magnetic field on the UHECR correlation studies
2022年11月4日(金) 14:00 - 15:00
樋口 諒 (理化学研究所 開拓研究本部 (CPR) 長瀧天体ビッグバン研究室 基礎科学特別研究員)
Telescope Array (TA) and Auger experiments reported anisotropies in the arrival direction of ultra-high-energy cosmic rays (UHECRs). In the current correlation studies between UHECRs and source candidates, the Auger experiment reported a correlation between the flux model of assumed sources and UHECR events and suggested a 10% contribution of starburst galaxies (SBGs) to the anisotropy of UHECRs. However, they do not consider the effect of coherent deflection by the galactic magnetic field (GMF), and they should significantly affect the results of the correlation studies. In this talk, we introduce a current study of UHECR anisotropy and the effect of GMF on them.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Magnetic fields at extragalactic scales: origin from the early universe?
2022年10月7日(金) 14:00 - 15:00
難波 亮 (理化学研究所 数理創造プログラム (iTHEMS) 上級研究員)
Blazar observations have provided tantalizing evidence for the presence of magnetic fields in the extragalactic regions, where astrophysical processes may not be an efficient source for their generation. While a natural speculation is to associate the production of such large-scale magnetic fields to inflationary physics, it has been known that magnetogenesis solely from inflation is quite challenging. In this talk I will discuss some mechanisms, successful/unsuccessful, for production of magnetic fields in the primordial universe, as well as the constraints from theoretical consistencies and observational data.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Hyperons in neutron stars: fast cooling, Joule heating and hyperon superfluidity
2022年9月26日(月) 14:00 - 15:00
Filippo Anzuini (Postdoc Fellow, Department of Astronomy, Monash University, Australia)
Neutron stars challenge current models of highly dense matter. Despite be- ing the targets of numerous observational campaigns (e.g. gravitational-wave searches and X-ray observations), their equation of state is still unknown. One of the most exciting possibilities is that “unconventional” particles such as hy- perons may appear in neutron star cores. Hyperons have a major impact on the observed thermal luminosity, because they accelerate the cooling rate via direct Urca processes, which copiously increase the neutrino emission from the core. Such mechanism is often considered to be a key signature of hyperon concentrations at high densities. Hyperon superfluidity plays a major role as well, because it can suppress the neutrino emissivity exponentially. The hope is that a comparison of the theoretical cooling curves against the available data of thermally-emitting neutron star can hint towards the existence of hyperons and their superfluidity. There is one ingredient, however, that is often neglected in neutron star cooling models: internal heating. The magnetic field of neutron stars decays due to the dissipation of the electric currents circulating in the crust, generating substantial Joule heating in the shallower layers. The ther- mal power generated by this process can counterbalance hyperon fast cooling, making it difficult to infer the presence of hyperons from the available thermal luminosity data, and complicating the link between measured thermal emission and internal composition. We show that this is the case for magnetars, because their crustal temperature is almost independent of hyperon direct Urca cooling in the core, regardless of whether hyperons are superfluid or not. Likewise, ther- mal luminosity data of moderately magnetized neutron stars are not suitable to extract information about the internal composition, as long as hyperons are superfluid.
会場: コモンルーム 246-248号室 とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
MeV gamma-ray all sky simulation
2022年9月16日(金) 14:00 - 15:00
辻 直美 (神奈川大学 理学部 特別助教)
The MeV gamma-ray domain is the only unexplored window among recent multiwavelength observations in astrophysics, often referred to as the "MeV gap". To fulfill this gap, there are several ongoing and planned projects of MeV gamma-ray telescopes. The measurement of MeV gamma rays (both continuum and line emission) would give us new insight into many topics in astrophysics, such as relativistic jets, particle acceleration, and origin of matter. In advance of the future MeV gamma-ray missions, we have been working on prediction of the MeV gamma-ray sky, which is helpful to determine what kinds of sources can be detectable with the future telescopes. In order to explore the MeV gamma-ray sources, we performed a catalog cross-matching between the hard X-ray (Swift/BAT) and GeV gamma-ray (Fermi/LAT) catalogs, resulting in 145 firmly cross-matched sources. Combined with the Galactic diffuse emission, which is calculated by GALPROP to reconcile the cosmic-ray and gamma-ray spectra with observations by AMS-02, Voyager, and Fermi-LAT, the all-sky maps in the MeV gamma-ray band can be produced. This is also used to investigate a long-standing problem in the MeV gamma-ray astrophysics: the origin of the diffuse emission from the inner Galaxy, measured by COMPTEL. I will report the analysis and results in detail, and introduce future missions of the MeV gamma-ray detectors.
会場: via Zoom
イベント公式言語: 英語