New estimates of neutron star size and Hubble constant

Multi-messenger astronomy.

A combination of astrophysical estimations has permitted scientists to put new constraints on the radius of a typical neutron star and give a novel calculation of the Hubble constant that demonstrates the rate at which the universe is expanding.

Scientists got these outcomes by studying signals coming out from several sources, for example, recently observed mergers of neutron stars. They analyzed gravitational-wave signals and electromagnetic emissions from the mergers and combined them with previous mass measurements of pulsars or recent results from NASA’s Neutron Star Interior Composition Explorer.

They found that the radius of a typical neutron star is about 11.75 kilometers and the Hubble constant is approximately 66.2 kilometers per second per megaparsec.

Ingo Tews, a theorist in Nuclear and Particle Physics, Astrophysics and Cosmology group at Los Alamos National Laboratory, said, “Combining signals to gain insight into distant astrophysical phenomena is known in the field as multimessenger astronomy. In this case, the researchers’ multimessenger analysis allowed them to restrict the uncertainty of their estimate of neutron star radii to within 800 meters.”

Collision of two neutron stars showing the electromagnetic and gravitational-wave emissions during the merger process
Collision of two neutron stars showing the electromagnetic and gravitational-wave emissions during the merger process. The combined interpretation of multiple messengers allows astrophysicists to understand the internal composition of neutron stars and to reveal the properties of matter under the most extreme conditions in the universe. Credit: Tim Dietrich

No matter what, this novel approach of measuring the Hubble constant contributes to a debate that has arisen from other, competing determinations of the universe’s expansion. The uncertainties in the new multimessenger Hubble calculation are too large to resolve the disagreement definitively, but the measurement is slightly more supportive of the CMB approach.

Tews’ primary scientific role in the study was to provide the input from nuclear theory calculations that are the starting point of the analysis. His seven collaborators on the paper comprise an international team of scientists from Germany, the Netherlands, Sweden, France, and the United States.

Journal Reference:
  1. T. Dietrich at Universität Potsdam in Potsdam, Germany el al., “Multimessenger constraints on the neutron-star equation of state and the Hubble constant,” Science (2020). DOI: 10.1126/science.abb4317

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