Capture rates of compact objects by supermassive black holes

Capture rates of compact objects were calculated by using a recent solution of the Fokker-Planck equation in energy space, including two-body resonant effects. The fraction of compact objects (white dwarfs, neutron stars, and stellar black holes) was estimated as a function of the luminosity of the galaxy from a new grid of evolutionary models. Stellar mass densities at the influence radius of central supermassive black holes were derived from brightness profiles obtained by Hubble Space Telescope observations. The present study indicates that the capture rates scale as proportional to M-bh(-1.048), a consequence of the fact that dwarf galaxies have denser central regions than luminous objects. If the mass distribution of supermassive black holes has a lower cutoff at similar to 1.4x10(6)M (corresponding to the lowest observed supermassive black hole mass, located in M32), then nine inspiral events are expected to be seen by the Laser Interferometer Space Antenna (7-8 corresponding to white dwarf captures and 1-2 to neutron star and stellar black hole captures) after 1 yr of operation. However, if the mass distribution extends down to similar to 2x10(5)M, then the total number of expected events increases up to 579 (corresponding to similar to 274 stellar black hole captures, similar to 194 neutron star captures, and similar to 111 white dwarf captures).