An x-ray satellite has observed superhot gas--millions of degrees Celsius--whirling at close to the speed of light. The gas is apparently being sucked into a massive, rotating black hole in another galaxy. The finding provides some of the best evidence yet that some black holes rotate.

No one knows how many black holes rotate, and it's possible that all of them do. To find out, you have to observe the x-rays spewed from material near the edge of the black hole--the stuff that's about to fall into it--and that's no mean feat when the black hole is many millions of light-years away. Earlier observations have suggested that some black holes rotate, but the measurements were by no means definitive. Last year, astronomers got a much more capable tool: the European Space Agency's XMM-Newton satellite, which can measure x-rays more precisely than other satellites can.

Astronomer Masao Sako of Columbia University in New York City analyzed x-rays from the nuclei of two galaxies. The radiation emitted by carbon, oxygen, and nitrogen molecules was smeared from its standard frequencies, suggesting that the gases are orbiting at close to the speed of light, at the very edge of the black hole. The observations also suggest that the black hole must be spinning: The disk of gas extends very close to the black hole's edge, which can only happen if the black hole is rotating, because general relativity predicts that there are no stable orbits close to the edge of a nonrotating black hole. The results were announced 6 December at a press conference in Paris and will be published in the January issue of Astronomy and Astrophysics.

The team's interpretation of the x-ray spectra "may be correct, but it's certainly not the end" for other models of what's going on in the two galaxies, says astronomer Joachim Trümper of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. But Johan Bleeker of the Space Organization Netherlands in Utrecht says, "This is one of the outstanding results of XMM-Newton so far."

--GOVERT SCHILLING

Related sites

XMM-Newton's home page

First science results from XMM-Newton

Journey into a black hole