Tidal Interaction between a Fluid Star and a Kerr Black Hole in Circular Orbit

Paul Wiggins; Dong Lai

doi:10.1086/308565

paper

Tidal Interaction between a Fluid Star and a Kerr Black Hole in Circular Orbit

arXiv:astro-ph/9907365 · doi:10.1086/308565

Abstract

We present a semi-analytic study of the equilibrium models of close binary systems containing a fluid star (mass $m$ and radius $R_{0}$ ) and a Kerr black hole (mass $M$ ) in circular orbit. We consider the limit $M ≫ m$ where spacetime is described by the Kerr metric. The tidally deformed star is approximated by an ellipsoid, and satisfies the polytropic equation of state. The models also include fluid motion in the stellar interior, allowing binary models with nonsynchronized stellar spin (as expected for coalescing neutron star-black hole binaries) to be constructed. Tidal disruption occurs at orbital radius $r_{tide} \sim R_{0} (M / m)^{1/3}$ , but the dimensionless ratio $r^_{tide} = r_{tide} / [R_{0} (M / m)^{1/3}]$ depends on the spin parameter of the black hole as well as on the equation of state and the internal rotation of the star. We find that the general relativistic tidal field disrupts the star at a larger $r^_{tide}$ than the Newtonian tide; the difference is particularly prominent if the disruption occurs in the vicinity of the black hole's horizon. In general, $r^_{tide}$ is smaller for a (prograde rotating) Kerr black hole than for a Schwarzschild black hole. We apply our results to coalescing black hole-neutron star and black hole-white dwarf binaries. The tidal disruption limit is important for characterizing the expected gravitational wave signals and is relevant for determining the energetics of gamma ray bursts which may result from such disruption.

29 pages including 8 figures. Minor changes and update. To appear in ApJ, March 20, 2000 (Vol.532, #1)

Tidal Interaction between a Fluid Star and a Kerr Black Hole in Circular Orbit

Abstract

References in corpus (2)

Cited by in corpus (36)