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General Relativity and Quantum Cosmology, gr-qc, Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
Abstract:
On August 17, 2017, the LIGO and Virgo observatories made the first direct
detection of gravitational waves from the coalescence of a neutron star binary
system. The detection of this gravitational wave signal, GW170817, offers a
novel opportunity to directly probe the properties of matter at the extreme
conditions found in the interior of these stars. The initial,
minimal-assumption analysis of the LIGO and Virgo data placed constraints on
the tidal effects of the coalescing bodies, which were then translated to
constraints on neutron star radii. Here, we expand upon previous analyses by
working under the hypothesis that both bodies were neutron stars that are
described by the same equation of state and have spins within the range
observed in Galactic binary neutron stars. Our analysis employs two methods:
the use of equation-of-state-insensitive relations between various macroscopic
properties of the neutron stars and the use of an efficient parameterization of
the defining function $p(\rho)$ of the equation of state itself. From the LIGO
and Virgo data alone and the first method, we measure the two neutron star
radii as $R_1=10.8^{+2.0}_{-1.7}$ km for the heavier star and $R_2=
10.7^{+2.1}_{-1.5}$ km for the lighter star at the 90% credible level. If we
additionally require that the equation of state supports neutron stars with
masses larger than $1.97 \,M_\odot$ as required from electromagnetic
observations and employ the equation of state parametrization, we further
constrain $R_1= 11.9^{+1.4}_{-1.4}$ km and $R_2= 11.9^{+1.4}_{-1.4}$ km at the
90% credible level. Finally, we obtain constraints on $p(\rho)$ at supranuclear
densities, with pressure at twice nuclear saturation density measured at
$3.5^{+2.7}_{-1.7}\times 10^{34} \,\mathrm{dyn}/\mathrm{cm}^{2}$ at the 90%
level.
