A scalable random forest regressor for combining neutron-star equation of state measurements: A case study with GW170817 and GW190425

Abstract

Gravitational-wave observations of binary neutron star coalescences constrain the neutron-star equation of state by enabling measurement of the tidal deformation of each neutron star. This deformation is determined by the tidal deformability parameter $\hat{I}›$, which was constrained using the first binary neutron star gravitational-wave observation, GW170817. Now, with the measurement of the second binary neutron star, GW190425, we can combine different gravitational-wave measurements to obtain tighter constraints on the neutron-star equation of state. In this paper, we combine data from GW170817 and GW190425 to place constraints on the neutron-star equation of state. To facilitate this calculation, we derive interpolated marginalized likelihoods for each event using a machine learning algorithm. These likelihoods, which we make publicly available, allow for results from multiple gravitational-wave signals to be easily combined. Using these new data products, we find that the radius of a fiducial 1.4 $M_{\odot }$ neutron star is constrained to $11.6_{-0.9}^{+1.6}$ km at 90% confidence and the pressure at twice the nuclear saturation density is constrained to $3.1_{-1.3}^{+3.1}\times 10^{34}$ dyne/cm${}^2$ at 90% confidence. This result is dominated by GW170817 and is consistent with findings from other works.

6 pages, 3 figures. Accepted for publication in MNRAS