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General Relativity and Quantum Cosmology, gr-qc
Abstract:
LIGO and Virgo recently observed the first binary neutron star merger,
demonstrating that gravitational-waves offer the ability to probe how matter
behaves in one of the most extreme environments in the Universe. However, the
gravitational-wave signal emitted by an inspiraling binary neutron star system
is only weakly dependent on the equation of state and extracting this
information is challenging. Previous studies have focused mainly on binary
systems where the neutron stars are spinning slowly and the main imprint of
neutron star matter in the inspiral signal is due to tidal effects. For
binaries with non-negligible neutron-star spin the deformation of the neutron
star due to its own rotation introduces additional variations in the emitted
gravitational-wave signal. Here we explore whether highly spinning binary
neutron-star systems offer a better chance to measure the equation-of-state
than weakly spinning binary-neutron star systems. We focus on the dominant
adiabatic quadrupolar effects and consider three main questions. First, we show
that equation-of-state effects can be significant in the inspiral waveforms,
and that the spin-quadrupole effect dominates for rapidly rotating neutron
stars. Second, we show that variations in the spin-quadrupole phasing are
strongly degenerate with changes in the component masses and spins, and
neglecting these terms has a negligible impact on the number of observations
with second generation observatories. Finally, we explore the bias in the
masses and spins that would be introduced by using incorrect equation-of-state
terms. Using a novel method to rapidly evaluate an approximation of the
likelihood we show that assuming the incorrect equation-of-state when measuring
source parameters can lead to a significant bias. We also find that the ability
to measure the equation-of-state is improved when considering spinning systems.
