Multimessenger constraints on the neutron-star equation of state and the Hubble constant

Abstract

Observations of neutron-star mergers with distinct messengers, including gravitational waves and electromagnetic signals, can be used to study the behavior of matter denser than an atomic nucleus and to measure the expansion rate of the Universe as quantified by the Hubble constant. We performed a joint analysis of the gravitational-wave event GW170817 with its electromagnetic counterparts AT2017gfo and GRB170817A, and the gravitational-wave event GW190425, both originating from neutron-star mergers. We combined these with previous measurements of pulsars using x-ray and radio observations, and nuclear-theory computations using chiral effective field theory, to constrain the neutron-star equation of state. We found that the radius of a 1.4–solar mass neutron star is 11.75−0.81+0.86 km at 90% confidence and the Hubble constant is 66.2−4.2+4.4 at 1σ uncertainty.

Progress in Constraining Nuclear Symmetry Energy Using Neutron Star Observables Since GW170817

“…Interestingly, the most probable hadron-quark transition density ρ t /ρ 0 = 1.6 +1.2 −0.4 was found to be rather low, while the transition strength ∆ε/ε t = 0.4 +0. 20 −0.15 was modest and the speed of sound in QM c 2 QM /c 2 = 0.95 +0.05 −0.35 very high. The latter is understandable as the most probable transition density is very low, so the stiffness of QM EOS represented by its c 2 QM value has to be high enough to support the neutron star with a large QM core.…”

“…By comparing Equation (19) with the first relation of Equation (22) or Equation (20) with the second relation of Equation (22), one can immediately find that if the new expansion element ν sym is constructed reasonably, the dependence of E sym (ρ f ) on K sym or J sym at high densities should be reduced, as compared with the conventional approach, where the expansion element χ is unbounded from above.…”

“…Understanding the nature and constrain the Equation of State (EOS) of dense neutronrich nuclear matter is a major science goal [1][2][3][4] shared by many other astrophysical observations (see, e.g., the analyses and reviews in [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]) and terrestrial nuclear experiments (see, e.g., [22][23][24][25][26][27][28][29][30][31][32][33]). However, realizing this goal is very challenging for many scientific and technical reasons.…”

Fast-transient Searches in Real Time with ZTFReST: Identification of Three Optically Discovered Gamma-Ray Burst Afterglows and New Constraints on the Kilonova Rate

“…At this point, we have two optional features implemented. The first employs automated fits to kilonova light curve model grids, such as those provided by Kasen et al (2017) and Bulla (2019), combined with a Gaussian Process Regression framework (Coughlin et al 2018(Coughlin et al , 2019aDietrich et al 2020). In particular, due to the limited number of light curve points, we reduce dimensionality with single component light curve models by default; however, multiple component models with both "dynamical ejecta" and disk winds driven by neutrino energy, magnetic fields, viscous evolution and/or nuclear recombination are also available (e.g., Metzger et al 2008;Bauswein et al 2013;Dietrich & Ujevic 2017;Siegel & Metzger 2017).…”

“…With a Bayesian analysis (Pang et al, in preparation) on the data with a light curve model of a GRB afterglow (Ryan et al 2020), kilonova (Dietrich et al 2020) and the combination of both, the evidence for these 3 hypotheses are estimated. The Bayes factors for GRB afterglow against the combination of GRB afterglow and kilonova is found to be ∼ 10 3.42±0.08 .…”