January 11, 2001: The Hubble telescope may have, for the first
time, provided direct evidence for the existence of black holes
by observing how matter disappears when it falls beyond the
"event horizon," the boundary between a black hole and the
outside universe. Astronomers found their evidence by watching
the fading and disappearance of pulses of ultraviolet light from
clumps of hot gas swirling around a massive, compact object
called Cygnus XR-1. This activity suggests that the hot gas fell
into a black hole.See the rest: An event horizon is the
mysterious region surrounding a black hole that forever traps
light and matter straying nearby. No astronomical object other
than a black hole can possess an event horizon. Black holes have
been inferred by observing the furious whirlpool motion of
trapped gas and estimating how much mass is crammed into the
tiny region of space the black hole occupies. Previous X-ray
observations have offered evidence for an event horizon by
surveying black hole candidates that se