OBSERVATORY; Black Hole Forecast: A Cold Gas Cloud
By RITCHIE S. KING
Published: December 20, 2011
For the past 20 years, astrophysicists have been watching stars and other space matter swirling around Sagittarius A* (pronounced A-star), the black hole at the center of the Milky Way. But they have never seen anything sucked into it (or any other black hole, for that matter).
New infrared observations from the Very Large Telescope in northern Chile show a cold gas cloud headed almost directly toward the black hole at a speed faster than 1,000 miles per second. By 2013, part of the dust cloud will arrive at the hole's event horizon -- the point of no return.
The black hole's tremendous gravity should accelerate and compress the gas, heating it to at least 11 million degrees Fahrenheit, from just 440 degrees, and causing it to emit X-rays. Though astrophysicists have seen X-ray emissions like this before, they have never known for certain what produces them.
''Normally, all we do is see the light'' from the X-rays, said Eliot Quataert, an astronomer at the University of California, Berkeley, and a member of the team that published the observations in the journal Nature. ''And we have to figure out what happened.''
But this time astrophysicists will know what is happening, so they will get to see whether the X-rays actually behave according to theory.
DRAWING (DRAWING BY CHRIS GASH)