UA scientist looks into black hole

Almudena Alonso-Herrero leads an international team of astronomers who recently announced the discovery of a gas bar that appears to be "feeding" a huge black hole in a galaxy 10 million light years from Earth.

"We believe that this is the first direct evidence of molecular gas flowing into the center of an active galaxy," said Alonso-Herrero, a Steward Observatory research associate.

Active galaxies, some of the brightest objects in the sky, have supermassive black holes at the center of the galaxies. Astronomers believe these black holes, weighing millions of times more than our own sun, are powered by material falling into them.

But how this material gets to these black holes has puzzled scientists. The problem lies in explaining how material is dislodged from its orbit and funneled into the black hole.

"In a normal galaxy you have your material just orbiting around. You need to basically break this potential," Alonso-Herrero said. "You need to get the material closer because the black hole is not going to be able to reach out and get it."

Using images from the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope and ground-based telescopes in Australia, Alonso-Herrero and her team were able to detect an elbow-shaped bar that rotates around the galaxy like the propeller of an airplane. This bar, made up of gas and dust, acts as a conduit to channel material from its steady orbit into the black hole at the center of the Circinus galaxy.

Alonso-Herrero announced the discovery of the gas bar last week at the 193rd Meeting of the American Astronomical Society in Austin, Texas.

Now that Alonso-Herrero's team has discovered the gas bar, the next question is whether Circinus is representative of other active galaxies.

"We don't know if this is common or not," She said, noting that the only way to be sure would be to study other galaxies.

The team chose the Circinus galaxy because it is one of the nearest active galaxies. Detecting a gas bar that is only a few hundred light years across is difficult even with the largest telescopes.

Alonso-Herrero said that studying galaxies farther away from Earth would be dependent on the production of bigger, more powerful telescopes. There is of course a galaxy closer than Circinus - our own, but studying our own galaxy poses a major problem to astronomers.

"We look through our own galaxy sideways and so everything along the line of sight to the center has to be picked apart," said Marcea Reike, a UA astronomy professor who also worked on the team. "It's hard to tell the outline of the forest if you're in the middle of it."

Reike said that the NICMOS infrared instrument on the Hubble Space Telescope works well for studying black holes because unlike ground-based telescopes, it doesn't have to cut through the atmosphere.

"The atmosphere absorbs light, defocuses it, moves it all around," Reike said. "It's a general bad actor."

She said the Hubble can't be used in the infrared presently because the coolant ran out on NICMOS. NASA has planned a repair mission next year.

Until then, Alonso-Herrero, Reike and the other members of the international team will be busy finalizing the formal presentation of their recent discovery.

"What we've done is a big step forward. We have to kind of finish digesting it," Reike said.