Stellar dynamics of extrememassratio inspirals
Abstract
Inspiral of compact stellar remnants into massive black holes (MBHs) is accompanied by the emission of gravitational waves at frequencies that are potentially detectable by spacebased interferometers. Event rates computed from statistical (FokkerPlanck, MonteCarlo) approaches span a wide range due to uncertaintities about the rate coefficients. Here we present results from direct integration of the postNewtonian Nbody equations of motion describing dense clusters of compact stars around Schwarzschild MBHs. These simulations embody an essentially exact (at the postNewtonian level) treatment of the interplay between stellar dynamical relaxation, relativistic precession, and gravitationalwave energy loss. The rate of capture of stars by the MBH is found to be greatly reduced by relativistic precession, which limits the ability of torques from the stellar potential to change orbital angular momenta. Penetration of this “Schwarzschild barrier” does occasionally occur, resulting in capture of stars onto orbits that gradually inspiral due to gravitational wave emission; we discuss two mechanisms for barrier penetration and find evidence for both in the simulations. We derive an approximate formula for the capture rate, which predicts that captures would be strongly disfavored from orbits with semimajor axes below a certain value; this prediction, as well as the predicted rate, are verified in the Nbody integrations. We discuss the implications of our results for the detection of extrememassratio inspirals from galactic nuclei with a range of physical properties.
 Publication:

Physical Review D
 Pub Date:
 August 2011
 DOI:
 10.1103/PhysRevD.84.044024
 arXiv:
 arXiv:1102.3180
 Bibcode:
 2011PhRvD..84d4024M
 Keywords:

 04.30.Db;
 04.25.Nx;
 04.80.Cc;
 Wave generation and sources;
 PostNewtonian approximation;
 perturbation theory;
 related approximations;
 Experimental tests of gravitational theories;
 Astrophysics  Cosmology and Extragalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 28 pages, 16 figures. Version 2 is significantly revised to reflect new insights into J and Q effects, to be published later