ISO observations of the Galactic Center black hole candidates 1E 1740.7-2942 and GRS 1758-258

The Galactic Center black hole candidates IE 1740.7-2942 and GRS 1758 are l uminous hard X-ray sources, with L-x > 10(37) erg s(-1). It has been sugges ted that both of these sources are powered by Bondi-Hoyle accretion from th e ambient dense interstellar medium. If this is the case, luminous far-infr ared fine-structure line emission should he detectable from both sources. W e have obtained Infrared Space Observatory observations of both sources and failed to detect emission at the predicted levels, implying that either (1 ) the hard X-ray luminosities averaged over the last century are considerab ly lower (by factors of greater than or similar to 3 - 5) than presently, o r (2) the mass of gas in immediate proximity to the sources is smaller than in the models (which assumed the X-ray sources were embedded in dense ISM) by about the same factor. Option (2) seems more likely, implying that thes e sources are not fueled by Bondi-Hoyle accretion.