CAN ISOLATED STELLAR-MASS BLACK-HOLES EXPLAIN THE HARD X-RAY SOURCES IN THE GALACTIC-CENTER REGION

It has been proposed that the X-ray source 1E 1740.7-2942 might be the first example of an isolated stellar-mass black hole directly accreting from a molecular cloud. This scenario rests on the unusual radio, IR, and gamma-ray properties of 1 E 1740.7 - 2942 and on its spatial coincidence with one of the dense molecular clouds of the Galactic center region. Based on a model for the birth rate of compact stellar remnants and their evolution in the Galactic gravitational potential, we estimate the probability of such an association. Although the conditions in the Galactic center regions are the most favorable for the presence of neutron stars and black holes inside dense molecular clouds, the requirements necessary to allow a sufficiently high accretion rate strongly reduce the probability of observing these kind of objects.