The Losscone Problem in Axisymmetric Nuclei
Abstract
We consider the problem of consumption of stars by a supermassive black hole (SBH) at the center of an axisymmetric galaxy. Inside the SBH sphere of influence, motion of stars in the mean field is regular and can be described analytically in terms of three integrals of motion: the energy E, the zcomponent of angular momentum L_{z} , and the secular Hamiltonian H. There exist two classes of orbits, tubes and saucers; saucers occupy the lowangularmomentum parts of phase space and their fraction is proportional to the degree of flattening of the nucleus. Perturbations due to gravitational encounters lead to diffusion of stars in integral space, which can be described using the FokkerPlanck equation. We calculate the diffusion coefficients and solve this equation in the twodimensional phase space (L_{z} , H), for various values of the capture radius and the degree of flattening. Capture rates are found to be modestly higher than in the spherical case, up to a factor of a few, and most captures take place from saucer orbits. We also carry out a set of collisional Nbody simulations to confirm the predictions of the FokkerPlanck models. We discuss the implications of our results for rates of tidal disruption and capture in the Milky Way and external galaxies.
 Publication:

The Astrophysical Journal
 Pub Date:
 September 2013
 DOI:
 10.1088/0004637X/774/1/87
 arXiv:
 arXiv:1301.3150
 Bibcode:
 2013ApJ...774...87V
 Keywords:

 galaxies: evolution;
 galaxies: nuclei;
 Astrophysics  Galaxy Astrophysics
 EPrint:
 27 pages, 14 figures, matches ApJ accepted version. Software for computing capture rates is available at http://td.lpi.ru/~eugvas/losscone/