Nonparametric inference of the neutron star equation of state from gravitational wave observations

Philippe Landry and Reed Essick
Phys. Rev. D 99, 084049 – Published 30 April 2019

Abstract

We develop a nonparametric method for inferring the universal neutron star (NS) equation of state (EOS) from gravitational wave (GW) observations. Many different possible realizations of the EOS are generated with a Gaussian process conditioned on a set of nuclear-theoretic models. These synthetic EOSs are causal and thermodynamically stable by construction, span a broad region of the pressure-density plane, and can be selected to satisfy astrophysical constraints on the NS mass. Associating every synthetic EOS with a pair of component masses M1,2 and calculating the corresponding tidal deformabilities Λ1,2, we perform Monte Carlo integration over the GW likelihood for M1,2 and Λ1,2 to directly infer a posterior process for the NS EOS. We first demonstrate that the method can accurately recover the properties of an injected GW signal, and subsequently use it to analyze data from GW170817, finding a canonical deformability of Λ1.4=160113+448 and p(2ρnuc)=1.351.2+1.8×1034dyn/cm2 for the pressure at twice the nuclear saturation density at 90% confidence, in agreement with previous studies, when assuming a loose EOS prior. With a prior more tightly constrained to resemble the theoretical EOS models, we recover Λ1.4=556172+163 and p(2ρnuc)=4.732.5+1.4×1034dyn/cm2. We further infer the maximum NS mass supported by the EOS to be Mmax=2.090.16+0.37 (2.040.002+0.22) M with the loose (tight) prior. The Bayes factor between the two priors is BIA1.12, suggesting that neither is strongly preferred by the data and that constraints on the EOS from GW170817 alone may be sensitive to the choice of prior.

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  • Received 5 December 2018

DOI:https://doi.org/10.1103/PhysRevD.99.084049

© 2019 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Philippe Landry*

  • Enrico Fermi Institute and Kavli Institute for Cosmological Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA

Reed Essick

  • Kavli Institute for Cosmological Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA

  • *landryp@uchicago.edu
  • reedessick@kicp.uchicago.edu

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Vol. 99, Iss. 8 — 15 April 2019

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