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تسجيل مستخدم جديدFormation of mass gap compact object and black hole binary from Population III stars
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We performed population synthesis simulations of Population III binary stars with Maxwellian kick velocity distribution when MGCOs (Mass Gap Compact Objects with mass 2--5$,M_{odot}$) are formed. We found that for eight kick velocity dispersion models of $sigma_{rm k}=0$--$500$ km/s, the mean mass of black hole (BH)-MGCO binary is $sim (30 ,M_odot,,2.6 ,M_odot)$. In numerical data of our simulations, we found the existence of BH-MGCO binary with mass $(22.9 ,M_odot,,2.5 ,M_odot)$ which looks like GW190814.
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We perform a binary population synthesis calculation incorporating very massive population (Pop.) III stars up to 1500 $M_odot$, and investigate the nature of binary black hole (BBH) mergers. Above the pair-instability mass gap, we find that the typi
cal primary black hole (BH) mass is 135-340 $M_odot$. The maximum primary BH mass is as massive as 686 $M_odot$. The BBHs with both of their components above the mass gap have low effective inspiral spin $sim$ 0. So far, no conclusive BBH merger beyond the mass gap has been detected, and the upper limit on the merger rate density is obtained. If the initial mass function (IMF) of Pop. III stars is simply expressed as $xi_m(m) propto m^{-alpha}$ (single power law), we find that $alpha gtrsim 2.8$ is needed in order for the merger rate density not to exceed the upper limit. In the future, the gravitational wave detectors such as Einstein telescope and Pre-DECIGO will observe BBH mergers at high redshift. We suggest that we may be able to impose a stringent limit on the Pop. III IMF by comparing the merger rate density obtained from future observations with that derived theoretically.
In the case of zero-metal (population III or Pop III) stars, we show that the total mass of binary black holes from binary Pop III star evolution can be $sim 150 ,M_{odot}$, which agrees with the mass of the binary black hole GW190521 recently discov
ered by LIGO/Virgo. The event rate of such binary black hole mergers is estimated as 0.13--0.66$~(rho_{rm SFR}/(6times10^5~M_{odot}/{rm Mpc}^3))~Err_{rm sys}~{rm yr^{-1}~Gpc^{-3}}$, where $rho_{rm SFR}$ and $Err_{rm sys}$ are the cumulative comoving mass density of Pop III stars depending on star formation rate and the systematic errors depending on uncertainties in the Pop III binary parameters, respectively. The event rate in our fiducial model with $rho_{rm SFR}=6times10^5~M_{odot}/{rm Mpc}^3$ and $ Err_{rm sys}=1$ is 0.13--0.66$~{rm yr^{-1}~Gpc^{-3}}$, which is consistent with the observed value of 0.02--0.43$~{rm yr^{-1}~Gpc^{-3}}$.
We study formation of stellar mass binary black holes (BBHs) originating from Population III (PopIII) stars, performing stellar evolution simulations for PopIII binaries with MESA. We find that a significant fraction of PopIII binaries form massive B
BHs through stable mass transfer between two stars in a binary, without experiencing common envelope phases. We investigate necessary conditions required for PopIII binaries to form BBHs coalescing within the Hubble time with a semi-analytical model calibrated by the stellar evolution simulations. The formation efficiency of coalescing PopIII BBHs is estimated for two different initial conditions for PopIII binaries with large and small separations, respectively. Consequently, in both models, $sim 10%$ of the total PopIII binaries form BBHs only through stable mass transfer and $sim 10%$ of these BBHs merge due to gravitational wave emission within the Hubble time. Furthermore, the chirp mass of merging BBHs has a flat distribution over $15lesssim M_{rm chirp}/M_odot lesssim 35$. This formation pathway of PopIII BBHs is presumably robust because stable mass transfer is less uncertain than common envelope evolution, which is the main formation channel for Population II BBHs. We also test the hypothesis that the BBH mergers detected by LIGO originate from PopIII stars using our result and the total number of PopIII stars formed in the early universe as inferred from the optical depth measured by Planck. We conclude that the PopIII BBH formation scenario can explain the mass-weighted merger rate of the LIGOs O1 events with the maximal PopIII formation efficiency inferred from the Planck measurement, even without BBHs formed by unstable mass transfer or common envelope phases.
We review the main physical processes that lead to the formation of stellar binary black holes (BBHs) and to their merger. BBHs can form from the isolated evolution of massive binary stars. The physics of core-collapse supernovae and the process of c
ommon envelope are two of the main sources of uncertainty about this formation channel. Alternatively, two black holes can form a binary by dynamical encounters in a dense star cluster. The dynamical formation channel leaves several imprints on the mass, spin and orbital properties of BBHs.
Focusing on the remnant black holes after merging binary black holes, we show that ringdown gravitational waves of Population III binary black holes mergers can be detected with the rate of $5.9-500~{rm events~yr^{-1}}~({rm SFR_p}/ (10^{-2.5}~M_odot~
{rm yr^{-1}~Mpc^{-3}})) cdot ({rm [f_b/(1+f_b)]/0.33})$ for various parameters and functions. This rate is estimated for the events with SNR$>8$ for the second generation gravitational wave detectors such as KAGRA. Here, ${rm SFR_p}$ and ${rm f_b}$ are the peak value of the Population III star formation rate and the fraction of binaries, respectively. When we consider only the events with SNR$>35$, the event rate becomes $0.046-4.21~{rm events~yr^{-1}}~({rm SFR_p}/ (10^{-2.5}~M_odot~{rm yr^{-1}~Mpc^{-3}})) cdot ({rm [f_b/(1+f_b)]/0.33})$. This suggest that for remnant black holes spin $q_f>0.95$ we have the event rate with SNR$>35$ less than $0.037~{rm events~yr^{-1}}~({rm SFR_p}/ (10^{-2.5}~M_odot~{rm yr^{-1}~Mpc^{-3}})) cdot ({rm [f_b/(1+f_b)]/0.33})$, while it is $3-30~{rm events~yr^{-1}}~({rm SFR_p}/ (10^{-2.5}~M_odot~{rm yr^{-1}~Mpc^{-3}})) cdot ({rm [f_b/(1+f_b)]/0.33})$ for the third generation detectors such as Einstein Telescope. If we detect many Population III binary black holes merger, it may be possible to constrain the Population III binary evolution paths not only by the mass distribution but also by the spin distribution.
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