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

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Science  18 Dec 2020:
Vol. 370, Issue 6523, pp. 1450-1453
DOI: 10.1126/science.abb4317

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A combined multimessenger analysis

Neutron stars are stellar remnants with densities greater than that of an atomic nucleus. The properties of matter under such extreme conditions are poorly understood and inaccessible to terrestrial laboratories. Dietrich et al. developed a framework to combine multiple constraints on the masses and radii of neutron stars, including data from gravitational waves, electromagnetic observations, and theoretical nuclear physics calculations. They used this analysis to constrain the neutron-star equation of state and also improved the precision on the gravitational wave (standard siren) measurement of the Hubble constant—the expansion rate of the Universe.

Science, this issue p. 1450

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 11.750.81+0.86 km at 90% confidence and the Hubble constant is 66.24.2+4.4 at 1σ uncertainty.

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