AEI: How Big Is a Neutron Star?

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AEI: How Big Is a Neutron Star?

Post by bystander » Tue Mar 10, 2020 5:48 pm

How Big Is a Neutron Star?
Albert Einstein Institute | Max Plank Institute for Gravitational Physics | 2020 Mar 10

International team uses a novel approach combining gravitational-wave observations, multi-messenger astronomy, and nuclear physics to obtain the best measurement of neutron star size to date.

An international research team ... has obtained new measurements of how big neutron stars are. To do so, they combined a general first-principles description of the unknown behavior of neutron star matter with multi-messenger observations of the binary neutron star merger GW170817. Their results ... are more stringent by a factor of two than previous limits and show that a typical neutron star has a radius close to 11 kilometers. They also find that neutron stars merging with black holes are in most cases likely to be swallowed whole, unless the black hole is small and/or rapidly rotating. This means that while such mergers might be observable as gravitational-wave sources, they would be invisible in the electromagnetic spectrum. ...

Neutron stars are compact, extremely dense remnants of supernova explosions. They are about the size of a city with up to twice the mass of our Sun. How the neutron-rich, extremely dense matter behaves is unknown, and it is impossible to create such conditions in any laboratory on Earth. Physicists have proposed various models (equations of state), but it is unknown which (if any) of these models correctly describe neutron star matter in nature.

Mergers of binary neutron stars – such as GW170817, which was observed in gravitational waves and the entire electromagnetic spectrum in August 2017 – are the most exciting astrophysical events when it comes to learning more about matter at extreme conditions and the underlying nuclear physics. From this, scientists can in turn determine physical properties of neutron stars such as their radius and mass.

The research team used a model based on a first-principles description of how subatomic particles interact at the high densities found inside neutron stars. Remarkably, as the team shows, theoretical calculations at length scales less than a trillionth of a millimeter can be compared with observations of an astrophysical object more than a hundred million light years away. ...

GW170817: Stringent Constraints on Neutron-Star Radii
from Multimessenger Observations and Nuclear Theory
~ Collin D. Capano et al
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