Ataru Tanikawa

Abstract We present the merger rate density of Population III binary black holes (BHs) by means of a widely used binary population synthesis code BSE with extensions to very massive and extreme metal-poor stars. We consider not only low-mass BHs (lBHs: 5–50 M ⊙ ) but also high-mass BHs (hBHs: 130–200 M ⊙ ), where lBHs and hBHs are below and above the pair-instability mass gap (50–130 M ⊙ ), respectively. Population III BH–BHs can be categorized into three subpopulations: BH–BHs without hBHs (hBH

ABSTRACT GW190521 is a merger of two black holes (BHs), wherein at least one BH lies within the pair-instability (PI) mass gap, and it is difficult to form because of the effects of PI supernovae and pulsational PI (PPI). In this study, we examined the formation of GW190521-like BH-BHs under Population (Pop) III environments by binary population synthesis calculations. We reveal that convective overshooting in stellar evolution strongly affects the formation of GW190521-like BH-BHs. A model with

We have performed N-body simulations of globular clusters (GCs) in order to estimate a detection rate of mergers of Binary stellar-mass Black Holes (BBHs) by means of gravitational wave (GW) observatories. For our estimate, we have only considered mergers of BBHs which escape from GCs (BBH escapers). BBH escapers merge more quickly than BBHs inside GCs because of their small semi-major axes. N-body simulation can not deal with a GC with the number of stars N ~ 10^6 due to its high calculation co

We perform smoothed particle hydrodynamics simulations for merging binary carbon–oxygen (CO) WDs with masses of 1.1 and , until the merger remnant reaches a dynamically steady state. Using these results, we assess whether the binary could induce a thermonuclear explosion, and whether the explosion could be observed as a type Ia supernova (SN Ia). We investigate three explosion mechanisms: a helium-ignition following the dynamical merger ("helium-ignited violent merger model"), a carbon-ignition

Abstract We have studied double-detonation explosions in double-degenerate (DD) systems with different companion white dwarfs (WDs) for modeling Type Ia supernovae (SNe Ia) by means of high-resolution smoothed particle hydrodynamics (SPH) simulations. We have found that only the primary WDs explode in some of the DD systems, while the explosions of the primary WDs induce the explosions of the companion WDs in the other DD systems. The former case is a so-called dynamically-driven double-degenera

Abstract We investigate the formation of merging binary black holes (BHs) through isolated binary evolution, performing binary population synthesis calculations covering an unprecedentedly wide metallicity range of Population (Pop) I, II, III, and extremely metal-poor (EMP) binary stars. We find that the predicted merger rate density and primary BH mass ( m 1 ) distribution are consistent with the gravitational wave (GW) observations. Notably, Population III and EMP (<10 −2 Z ⊙ ) binary stars

Abstract We report the discovery of a candidate binary system consisting of a black hole (BH) and a red giant branch star in Gaia DR3. This binary system was discovered from 64,108 binary solutions for which both astrometric and spectroscopic data are available. For this system, the astrometric and spectroscopic solutions are consistent with each other, making this system a confident candidate of a BH binary. The primary (visible) star in this system, Gaia DR3 5870569352746779008, is a red giant

ABSTRACT Gaia BHs, black hole (BH) binaries discovered from data base of an astrometric telescope Gaia, pose a question to the standard binary evolution model. We have assessed whether Gaia BHs can be formed through dynamical capture in open clusters rather than through isolated binary evolution. We have performed gravitational N-body simulations of 100 open clusters with $10^5 \, \mathrm{M}_\odot$ in total for each metallicity Z = 0.02, 0.01, and 0.005. We have discovered one Gaia BH-like binar

Abstract We have investigated the effects of the hardness of primordial binaries on the whole evolution of star clusters by means of $N$-body simulations. Using a newly developed code, GORILLA, we simulated eleven $N$$=$ 16384 clusters with primordial binaries whose binding energies are equal in each cluster in the range of 1−300$kT_0$, where 1.5$kT_0$ is the average stellar kinetic energy at the initial time. We found that, in both the soft ($\le$3$kT_0$) and hard ($\ge$300$kT_0$) limits, clust

Abstract A large number of mergers of binary black holes (BHs) have been discovered by gravitational wave observations since the first detection of gravitational waves 2015. Binary BH mergers are the loudest events in the universe; however, their origin(s) have been under debate. There have been many suggestions for merging binary BHs. Isolated binary stars are one of the most promising origins. We have investigated the evolution of isolated binary stars ranging from zero metallicity (Population

ABSTRACT We infer the expected detection number of pair instability supernovae (PISNe) during the operation of the Euclid space telescope based on binary population models. Our models reproduce the global maximum at the primary BH mass of ∼9–10 M⊙ and the overall gradient of the primary BH mass distribution in the binary BH merger rate consistent with recent observations. We consider different PISN conditions depending on the 12C(α, γ)16O reaction rate. The fiducial and 3σ models adopt the stand

Abstract Population (Pop) III stars, first stars, or metal-free stars are made of primordial gas. We have examined if they can be dominant origins of merging binary black holes (BHs) and extremely metal-poor (EMP) stars. The abundance pattern of EMP stars is helpful to trace back the properties of Pop III stars. We have confirmed previous arguments that the observed BH merger rate needs Pop III star formation efficiency 10 times larger than theoretically predicted values, while the cosmic reioni