On the tidal evolution of the orbits of low-mass satellites around black holes

¹ Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia e-mail: andrej.cadez@fmf.uni-lj.si
² INAF - Astronomical Observatory of Padova, Vicolo Osservatorio 5, 35122 Padova, Italy

Received: 30 January 2008
Accepted: 21 May 2008

Abstract

Context. Low-mass satellites, like asteroids and comets, are expected to be present around the black hole at the Galactic center. We consider small bodies orbiting a black hole, and we study the evolution of their orbits due to tidal interaction with the black hole.

Aims. In this paper we investigate the consequences of the existence of plunging orbits when a black hole is present. We are interested in finding the conditions that exist when capture occurs.

Methods. Earlier analysis of the evolution of classical Keplerian orbits was extended to relativistic orbits around a Schwarzschild black hole.

Results. The main difference between the Keplerian and black hole cases is in the existence of plunging orbits. Orbital evolution, leading from bound to plunging orbits, goes through a “final” unstable circular orbit. On this orbit, tidal energy is released on a characteristic black hole timescale.

Conclusions. This process may be relevant for explaining how small, compact clumps of material can be brought onto plunging orbits, where they may produce individual short duration accretion events. The available energy and the characteristic timescale are consistent with energy released and the timescale typical of Galactic flares.