Using our population synthesis code, we found that the typical chirp mass
of binary black holes (BH-BHs) whose origin is the first star (Pop III) is
$\sim 30 M_\odot$ with the total mass of $\sim 60 M_\odot$ so that the inspiral chirp signal as
well as quasi normal mode (QNM) of the merging black hole are interesting
targets of LIGO,VIRGO, and KAGRA (Kinugawa et al.2014 and 2016). The
detection rate of the coalescing Pop III BH-BHs is $\sim 180$ events/yr in our
standard model. Furthermore, we found that the chirp mass has a peak at
$\sim 30 M_\odot$ in most of parameters and distribution functions (Kinugawa et
al.2016). This result predicted the gravitational wave events like GW150914
and LIGO paper said "recently predicted BBH total masses agree
astonishingly well with GW150914 and can have sufficiently long merger
times to occur in the nearby universe (Kinugawa et al. 2014)" (Abbot et al.
ApJL 818,22 (2016)).
There is a good chance to check indirectly the existence of Pop III massive
stars by gravitational waves.
Furthermore, we can simultaneously explain the formation of binaries that
consist of a BH and mass gap compact object (MGCO) with mass 2-5 $M_\odot$
(Kinugawa et al.2020) like GW190814,
and those consist of BHs with mass $\sim 80 M_\odot$ within the PISN mass gap for Pop
III stars like GW190521.
It is very interesting that Pop III model can interpret origins of three
different class of GW sources, that is, massive BH binary of mass 30Msun
like GW150914, BH and MGCO of mass
$2.5 M_\odot$ like GW190814, and very massive binary BH of $80 M_\odot$ like
GW190521.
It will be triple the fun!
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