spacetoday.net: Astronomers prove existence of black hole event horizon

Posted: Tue, Jan 10, 2006, 6:36 AM ET (1136 GMT)
Black hole event horizon (NASA/Dana Berry)

Astronomers said Monday that they have proven the existence of the event horizon, the "point of no return" that surrounds black holes. An MIT and Harvard team said they showed the existence of the event horizon, which by its nature is invisible, by looking for X-ray bursts from neutron stars and more compact objects thought to be black holes. The bursts, triggered when gas from nearby stars accumulates on the surface and explodes, are easily seen for neutron stars, but not for the black hole candidates. Astronomers interpreted the lack of x-ray busts from the black hole candidates as a sign that gas "disappeared" by passing across the object's event horizon, where gravity is so strong that the escape velocity exceeds the speed of light.