Science / Medicine : 4-Trillion-Mile Gas Bubble Studied

A bubble of hot gas nearly 4 trillion miles across is expanding at the center of the Milky Way galaxy, a finding that adds to evidence for a black hole there, German researchers reported last week in the British journal Nature. The bubble is growing by perhaps about 200 miles a second, said astronomer Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.

It is apparently being inflated by a powerful wind from Sagittarius A*, an object at the galactic center that is considered a possible black hole, the team said. Such a wind would be consistent with the presence of a black hole about 1 million times as massive as the sun.

The scientists also detected faint emissions of infrared energy that appeared to be coming from Sagittarius A*. Infrared emissions would be expected from a black hole, and the prior lack of observed infrared energy from Sagittarius A* had been one objection to considering it a black hole, said astronomer Paul Ho of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Still, the new observations do not constitute proof that Sagittarius A* is a black hole, he said. Scientists cannot view the center of the galaxy with an optical telescope because it is blocked by dust, Ho said.