Observations using the Hubble Space Telescope show matter disappearing as it falls beyond an event horizon.
If correct, this would be the first direct evidence for the existence of black holes.
An event horizon is
the predicted boundary round a black hole beyond which nothing – not even light – can escape. In the past,
the existence of black holes was inferred by observing orbiting stars and clouds of gas. The mass of the
central object can be estimated from the rotation velocity of the orbiting matter.
The new results,
presented at the American Astronomical Society meeting in San Diego earlier this year, track the ultraviolet
emission from hot clumps of gas circling the known black hole candidate Cygnus XR-1.
In two cases
the signature of the emission dims rapidly, exhibiting the “dying pulse train” predicted by theory, before
disappearing as it dips below the event horizon. The light dims as it is stretched by gravity to ever-longer
wavelengths in the approach to the black hole. The discovery was made during a new analysis of
observations dating from 1992. Work continues to find more such events and eliminate the possibility of
errors.
Observations using the Chandra X-ray satellite, also presented at the San Diego meeting,
confirm this picture. Chandra found a prodigious energy output from 12 X-ray neutron star systems – a
hundred times that from more massive black hole candidates.
