Universal Relations after GW170817

The equation of state of supranuclear matter is critical to the study of neutron stars, and is one of
the largest uncertainties in nuclear physics to date. The extraction of tidal deformabilities from the
gravitational waveforms of binary neutron star merger events, such as GW170817, is a promising
method of probing such nuclear structure. Previous studies have shown that approximately equation
of state insensitive relations exist between various neutron star observables. In particular, we study
the “I-Love-Q” and “binary Love” universal relations, which assist in reducing the uncertainty of
the dominant tidal effect in parameter estimation. In this talk, I will explain how one can reduce
equation of state variation for universal relations by restricting to only equations of state drawn
from the 90% posterior on pressure as a function of density, as derived by the LIGO Collaboration.
We find an improvement in binary Love universality by a factor of 59% for stars with mass ratio
0.75, and in I-Love-Q universality by 50%. I conclude by comparing systematic errors on tidal
measurement due to the equation of state variation with statistical errors and comment on whether
one can safely use these universal relations with future gravitational wave observations.