Authors: Pau Amaro-Seoane, Carlos Sopuerta, Patrick Brem
Date: 25 Oct 2012
Abstract: The capture of a compact object in a galactic nucleus by a massive black hole (MBH) is the best way to map space and time around it. It is well established that the event rate of stars kicked directly through the horizon (referred to as direct plunges) is much larger than the gradual inspiral due to the emission of gravitational waves. We prove that it is actually very difficult to get a compact object such a stellar black hole to be swallowed whole. A plunge will most likely be deflected into an EMRI orbit. They are simply very eccentric EMRIs and dominate the event rate. Moreover, if the central MBH is spinning, the net result on the rates is an enhancement, on both kinds of EMRIs. On the other hand, recent work on stellar dynamics has demonstrated that there seems to be a conspiracy in phase space, since rates decrease significantly by the presence of a blockade in the rate at which orbital angular momenta change takes place. This so-called "Schwarzschild barrier" is a result of the impact of relativistic precession on to the stellar potential torques and was first investigated by Merritt and collaborators. We confirm and quantify the existence of this barrier using a statistical sample of 2,500 direct-summation N-body simulations using both a post-Newtonian but also, and for the first time in a direct-summation integrator, a geodesic approximation for the relativistic orbits. Although the existence of the barrier prevents "traditional EMRIs" (i.e. EMRIs which are not very eccentric) from approaching the central MBH, very eccentric EMRIs, wrongly classified as plunges, insolently ignore the presence of the barrier. The combinations of these effects leads to the result that very eccentric orbits will dominate the rates.
© M. Vallisneri 2012 — last modified on 2010/01/29
Tantum in modicis, quantum in maximis