Statistics – Computation
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.........2l&link_type=abstract
Thesis (PHD). THE UNIVERSITY OF WISCONSIN - MADISON , Source DAI-B 59/05, p. 2247, Nov 1998, 100 pages.
Statistics
Computation
Scientific paper
Compact binaries containing black holes or neutron stars will eventually coalesce as a result of the loss of orbital angular momentum to gravitational radiation. The gravitational waves emitted during such an event are expected to contain much information about the equation of state at high densities, and furthermore, it is possible that these events could give rise to Gamma Ray Bursts, making these systems of great astrophysical interest. We have performed hydrodynamical simulations of the final stages of the coalescence of a black hole with a neutron star. Our computations are Newtonian throughout and have been carried out using the 'Smooth Particle Hydrodynamics' technique. The neutron star is modeled as a polytrope with an adiabatic index /Gamma=3. The black hole is represented by a point mass producing a Newtonian gravitational potential, and its horizon is modeled with an absorbing boundary at the Schwarschild radius. We have assumed tidal locking of the neutron star, so that the spin period matches the orbital rotation. We present results for different initial mass ratios (defined as the ratio of neutron star mass to black hole mass) in the binary. We calculate the gravitational radiation waveforms in the quadrupole approximation. Our results show that in every case we have studied, the neutron star is not completely disrupted by the initial encounter with the black hole. For high mass ratios (q>0.8) the system becomes hydrodynamically unstable and mass transfer from the neutron star onto the black hole occurs on an orbital time scale. For low mass ratios (q<0.3) no hydrodynamical instability develops and stable mass transfer occurs. The survival of the neutron star core implies that the entire coalescence process is more extended in time than was previously thought. This core could become unstable to explosion if driven below the minimum mass required for stability. To the limit of our resolution there is a baryon-free axis along the rotation axis of the binary system in every case, making these systems a promising source for the production of Gamma Ray Bursts.
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