Looking inside a neutron star

The new model will improve insights gleaned from gravitational waves.

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Gravitational waves from inspiraling neutron stars allow us to infer the as-of-yet unknown equation of the state of cold hadronic matter at supranuclear densities. During the inspiral, the dominant matter effects arise due to the star’s response to their companion’s tidal field, leaving a characteristic imprint in the emitted GW signal. This unique signature allows constraining the cold neutron star equation of state.

University of Birmingham researchers have illustrated how these particular vibrations, brought on by the interactions between the tidal forces of the two stars as they approach one another, affect gravitational-wave observations.

Considering these movements could make a massive difference to our understanding of the data taken by the Advanced LIGO and Virgo instruments, set up to detect gravitational waves generated by the merging of black holes and neutron stars.

The researchers want a new model prepared for Advanced LIGO’s upcoming observation run and even more sophisticated models for the A+ instruments, the next generation of Advanced LIGO equipment, whose initial observing run is scheduled to start in 2025.

Dr. Geraint Pratten of the Institute for Gravitational Wave Astronomy at the University of Birmingham is the lead author on the paper. He said: “Scientists can now get lots of crucial information about neutron stars from the latest gravitational wave detections. For example, the relationship between the star’s mass and radius provides crucial insight into the fundamental physics behind neutron stars. If we neglect these additional effects, our understanding of the structure of the neutron star as a whole can become deeply biased.”

Dr. Patricia Schmidt, a co-author of the paper and Associate Professor at the Institute for Gravitational Wave Astronomy, added“These refinements are significant. Within single neutron stars, we can start to understand what’s happening deep inside the star’s core, where matter exists at temperatures and densities we cannot produce in ground-based experiments. At this point, we might start to see atoms interacting with each other in ways we have not yet seen – potentially requiring new laws of physics.”

Journal Reference:

  1. Geraint Pratten, Patrica Schmidt and Natalie Williams. Impact of Dynamical Tides on the Reconstruction of the Neutron Star Equation of State. Phys. Rev. Lett. 129, 081102 – Published 18 August 2022. DOI: 10.1103/PhysRevLett.129.081102