A Dense Stellar Oddball

A Dense Stellar Oddball

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Mergers of a duo of binary neutron stars, such as GW 170817, provide a treasure trove of information about how matter behaves under such extreme conditions, as well as the underlying nuclear physics behind it. GW 170817 was first observed in gravitational waves and the entire electromagnetic spectrum in August 2017. From this type of important astrophysical event, scientists can go on to determine the physical properties of these oddball stars, including their radius and mass.

The research team at AEI used a model based on a first-principles description of how subatomic particles dance together at the extremely high densities found inside neutron stars. Remarkably, as the team of scientists discovered, 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 from Earth.

“It’s a bit mind boggling. GW 170817 was caused by the collision of two city-sized objects 120 million years ago, when dinosaurs were walking around here on Earth. This happened in a galaxy a billion trillion kilometers away. From that, we have gained insight into subatomic physics,” Dr. Capano commented in the March 10, 2020 Max Planck Institute Press Release.

The first-principles descriptions used by the scientists predicts numerous potential equations of state for neutron stars, which are directly derived from nuclear physics. From these possible equations of state, the researchers chose only those that are most likely to explain different astrophysical observations, which agree with gravitational-wave observations of GW 170817. The team used observations derived from public LIGO and Virgo data, which produce a brief hyper-massive neutron star as the result of the merger, and which agree with known constraints on the maximum neutron star mass from electromagnetic counterpart observations of GW 170817. This approach not only enabled the scientists to derive new information on dense-matter physics, but also to obtain the most stringent limits on the size of neutron stars to date.

“These results are exciting, not just because we have been able to vastly improve neutron star radii measurements, but because it gives us a window into the ultimate fate of neutron stars in merging binaries,” noted Stephanie Brown in the March 10, 2020 Max Planck Institute Press Release. Ms. Brown is co-author of the publication and a doctoral student at the AEI Hannover.

The new results suggest that, with an event like GW 170817, the LIGO and Virgo detectors at design sensitivity will be able to distinguish, from gravitational waves alone, whether the duo of neutron stars or duo of black holes have merged. For GW 170817, observations in the electromagnetic spectrum were central in making that important distinction.

The Laser Interferometer for Gravitational Wave Observatory (LIGO) is a large scale physics experiment and observatory to detect cosmic gravitational waves and to develop gravitational wave observatories on an astronomical level. The Virgo interferometer is a large interferometer designed to detect gravitational waves.

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