Thermodynamic Description of Inelastic Collisions in General Relativity

We discuss head-on collisions of neutron stars and disks of dust ("galaxies")following the ideas of equilibrium thermodynamics, which compares equilibriumstates and avoids the description of the dynamical transition processes betweenthem. As an always present damping mechanism, gravitational emission results infinal equilibrium states after the collision. In this paper we calculateselected final configurations from initial data of colliding stars and disks bymaking use of conservation laws and solving the Einstein equations. Comparinginitial and final states, we can decide for which initial parameters twocolliding neutron stars (non-rotating Fermi gas models) merge into a singleneutron star and two rigidly rotating disks form again a final (differentiallyrotating) disk of dust. For the neutron star collision we find a maximal energyloss due to outgoing gravitational radiation of 2.3% of the initial mass whilethe corresponding efficiency for colliding disks has the much larger limit of23.8%.Comment: 25 pages, 9 figure