Relativistic Studies of Close Neutron Star Binaries

TL;DR

This paper presents relativistic hydrodynamic simulations of close neutron star binaries, revealing new physical effects during merger and implications for gravitational wave detection.

Contribution

It introduces a novel (3+1)D relativistic simulation approach that captures effects absent in previous models, enhancing understanding of neutron star mergers.

Findings

Stars relax to a nearly non-spinning hydrodynamic state

Relativistic effects cause compression, heating, and neutrino emission

Black hole formation and lower-frequency inspiral are observed

Abstract

We discuss (3+1) dimensional general relativistic hydrodynamic simulations of close neutron star binary systems. The relativistic field equations are solved at each time slice with a spatial 3-metric chosen to be conformally flat. Against this solution the hydrodynamic variables and gravitational radiation are allowed to respond. We have studied four physical processes which occur as the stars approach merger. These include: 1) the relaxation to a hydrodynamic state of almost no spin; 2) relativistically driven compression, heating, and neutrino emission; 3) collapse to two black holes; and 4) orbit inspiral occurring at a lower frequency than previously expected. We give a brief account of the physical origin of these effects and an explanation of why they do not appear in models based upon, 1PN hydrodynamics, a weak field multipole expansion, a tidal analysis, or a rigidly corotating velocity field. The implication of these results for gravity wave detectors is also discussed.