Carrying fuel into the galactic center.

Carrying fuel into the galactic center

The Milky Way galaxy, like many others, has an intensely luminous center. A team of astronomers now reports identifying a stream of gas, 15 light-years long, that appears to mark the pathway by which gas is being funneled from a giant molecular cloud toward a massive, gaseous shell surrounding the galaxy's core. This gas streamer seems to be acting as a pipeline carrying fuel from a huge reservoir to the galaxy's central "engine."

"This may be the first evidence for the feeding of gas toward the center of the galaxy," says astrophysicist Paul T.P. Ho of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Because the Milky Way's center is only about 30,000 light-years away from Earth, studying the details of its behavior provides useful clues to what may be happening in quasars and other more distant, brighter objects. Ho and his collaborators reported their discovery at this week's meeting in Boston of the American Astronomical Society.

The streamer shows up in radio signals detected at a wavelength of 1 centimeter by the Very Large Array radio telescope near Socorro, N.M. Consisting almost entirely of molecular hydrogen from a nearby cloud, the streamer feeds gas toward a dusty, rotating, gaseous shell about 6 to 10 light-years from the galactic center. The streamer's flow speeds up, from 10 to 100 kilometers per second, as the gas gets closer to the shell.

The discovery is consistent with a proposal that places a compact, extremely massive object -- possibly a supermassive black hole -- at the Milky Way's center. Matter falling through such a strong gravitational field would release tremendous amounts of energy. A gas streamer provides a means by which fresh material can be continuously fed from a nearby reservoir to the shell and then into the black hole, which acts as a powerful energy source.

"One of the key problems that we want to resolve is what happens to this gas streamer as it gets closer," Ho says. "If it is really going into the galactic center, we expect its physical condition (temperature, density and so on) to change. We're trying to piece that together."

Ho and his colleagues also have observed that the gas streamer seems to originate where a supernova remnant impinges on the molecular cloud. The explosion of a massive star may have somehow "loosened up" the cloud's edge, making it easier for the material to be drawn toward the galactic center. "You can imagine whacking the cloud on its side, causing it to puff up a little along the edge," Ho says. "The part that puffs up gets sucked in."