His thesis research was on a mysterious, highly variable cosmic x-ray source. Later, when he was project scientist for the Uhuru X-ray Satellite, observations by the satellite were instrumental in showing that this source - Cygnus X-1 - was powered by matter falling into a black hole. Dr. Tananbaum received the NASA Exceptional Scientific Achievement Medal in 1980, the NASA Public Service Award in 1988, and the NASA Medal for Outstanding Leadership in 2000. He was elected a Fellow of the American Association for the Advancement of Science, and has served on numerous NASA and National Research Council advisory committees and as a Vice-president of the American Astronomical Society.