Thermodynamic Description of Inelastic Collisions in General Relativity

TL;DR

This paper applies thermodynamic principles to analyze inelastic collisions of neutron stars and dust disks in general relativity, calculating energy losses and final configurations using Einstein's equations.

Contribution

It introduces a thermodynamic framework to compare initial and final states of colliding astrophysical objects in general relativity, focusing on energy loss and final equilibrium states.

Findings

Neutron star collisions lose up to 2.3% of initial mass via gravitational radiation.

Dust disk collisions can lose up to 23.8% of initial mass.

Final configurations include merged neutron stars and reformed dust disks.

Abstract

We discuss head-on collisions of neutron stars and disks of dust ("galaxies") following the ideas of equilibrium thermodynamics, which compares equilibrium states and avoids the description of the dynamical transition processes between them. As an always present damping mechanism, gravitational emission results in final equilibrium states after the collision. In this paper we calculate selected final configurations from initial data of colliding stars and disks by making use of conservation laws and solving the Einstein equations. Comparing initial and final states, we can decide for which initial parameters two colliding neutron stars (non-rotating Fermi gas models) merge into a single neutron star and two rigidly rotating disks form again a final (differentially rotating) disk of dust. For the neutron star collision we find a maximal energy loss due to outgoing gravitational radiation of 2.3% of the initial mass while the corresponding efficiency for colliding disks has the much larger limit of 23.8%.