Blocking loweccentricity EMRIs: a statistical directsummation Nbody study of the Schwarzschild barrier
Abstract
The capture of a compact object in a galactic nucleus by a massive black hole (MBH), an extrememass ratio inspiral (EMRI), is the best way to map space and time around it. Recent work on stellar dynamics has demonstrated that there seems to be a complot in phase space acting on loweccentricity captures, since their rates decrease significantly by the presence of a blockade in the rate at which orbital angular momenta change takes place. This socalled `Schwarzschild barrier' is a result of the impact of relativistic precession on to the stellar potential torques, and thus it affects the enhancement on lower eccentricity EMRIs that one would expect from resonant relaxation. We confirm and quantify the existence of this barrier using a large number of directsummation Nbody simulations with both a postNewtonian and also, for the first time in a directsummation code, a geodesic approximation for the relativistic orbits. The existence of the barrier prevents loweccentricity EMRIs from approaching the central MBH via resonant relaxation. We confirm that the event rates for capture thus increase with the square of the distributed mass, in agreement with twobody relaxation. However, for nuclei with more than a few thousand M_{⊙} in the inner 10 mpc, twobody relaxation is so efficient that compact objects do not decouple into gravitational wavedriven inspirals but are mostly driven into direct plunges, if the central MBH is not spinning. This leads to an apparent maximum event rate of about 1 Myr^{1} for EMRIs originating from the inner 10 mpc.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 January 2014
 DOI:
 10.1093/mnras/stt1948
 arXiv:
 arXiv:1211.5601
 Bibcode:
 2014MNRAS.437.1259B
 Keywords:

 stars: black holes;
 stars: kinematics and dynamics;
 galaxies: kinematics and dynamics;
 galaxies: nuclei;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 10 pages, submitted