Gravitational radiation from and instabilities in compact stars and compact binary systems.

摘要

We have examined three types of compact astrophysical systems that are possible sources of detectable gravitational wave radiation (GWR): nonaxisymmetric pulsars; rapidly rotating compact stars undergoing the bar-mode instability; and coalescing compact binaries. Our analysis of nonaxisymmetric pulsars, based on the assumption that any equatorial asymmetries present in these objects were rotationally induced, indicates that nearby millisecond pulsars are generally better candidates for the detection of GWR than the Crab pulsar, which has been the object of an ongoing search for GWR (Tsubono 1991). Our finite difference hydrodynamics (FDH) simulation of an object encountering the rotationally induced bar-mode instability results in an ellipsoidal final configuration which, although gradually becoming more axisymmetric, persists for several orbits, continuously emitting GWR. We also have examined the stability and coalescence of equal mass binaries with polytropic, white dwarf (WD), and neutron star (NS) equations of state (EOS). In order for our explicit FDH code to be able to follow the coalescence of a binary system, it must proceed on a dynamical timescale. Hence, we began our investigation by performing FDH tests of the dynamical stability of individual models constructed along equilibrium sequences of binaries with the same total mass {dollar}Msb{lcub}T{rcub}{dollar} and EOS but decreasing separation, in order to determine if any models on these sequences were unstable to merger on a dynamical timescale. Our simulations indicate that no points of instability exist on the WD EOS sequences with {dollar}Msb{lcub}T{rcub}{dollar} =.500 {dollar}Msb{lcub}odot{rcub}{dollar} and 2.03 {dollar}Msbodot{dollar} or on the polytropic EOS sequences with polytropic indices n = 1.5 and 1.0. However, binary models on the n = 0.5 polytropic sequence and on two realistic NS EOS sequences were dynamically unstable to merger. Again using our FDH code, we followed the evolution of the binary with the minimum total energy and angular momentum on the n = 0.5 sequence through coalescence. At the end of the simulation, the ellipsoidal central object is encircled by spiral arms, ejected from the system during the merger, that have wrapped around on themselves and is continuing to emit low amplitude GWR.