Mergers of binary stars: The ultimate heavy-ion experience

The mergers of black hole-neutron star binaries are calcuated using a pseudo-general relativistic potential that incorporates O(v/c) post-Newtonian corrections. Both normal matter neutron stars and self-bound strange quark matter stars are considered as black hole partners. As long as the neutron stars are not too massive relative to the black hole mass, orbital decay terminates in stable mass transfer rather than an actual merger. For a normal neutron star, mass transfer results in a widening of the orbit but the stable transfer ends before the minimum neutron star mass is reached. For a strange star, mass transfer does not result in an appreciable enlargement of the orbital separation, and the stable transfer continues until the strange star essentially disappears. These differences might be observable through their respective gravitational wave signatures. Mergers of binary stars: The ultimate heavy-ion experience 2 The closest analog of a high-energy heavy-ion collision in nature is the gravitational wave-induced merger of two compact objects involving at least one neutron star or strange quark matter star in a binary system. However, since such a collision would involve more than 10 particles, it is vastly more energetic and would represent the ultimate heavy-ion experience. Such events have been suggested to occur frequently enough to account for some fractions of cosmological gamma-ray bursts and of r-process heavy elements [1]. In this work, we contrast the evolution of binary star mergers for two distinct cases: (1) A black hole (BH) and a (mostly) normal matter neutron star with a surface at which the pressure vanishes at vanishing baryon density. The interior of the star, however, may contain any or a combination of the many exotica such as hyperons, Bose (pion or kaon) condensate or quark matter. (2) A BH and a self-bound star with a surface at which the pressure vanishes at a large baryon density. This case is exemplified by a strange-quark matter (SQM) star [2] with a bare quark matter surface. Prototypes of these cases are shown as mass-radius relations in Fig. 1. Quantitative variations from these generic behaviors are caused by uncertainties in the strong interaction models (see the compendium of results in Fig. 2 of Ref. [3]), but do not lead to qualitative differences in gravitational mergers. The qualitative differences between the two classes of mass-radius relations will, however, produce significant changes in the outcomes of gravitational mergers. 0 0.5 1 1.5 2 2.5 M/M Sun 0 5 10 15 20