WASHINGTON, D.C.--Massive black holes at the centers of galaxies are insatiable, but astronomers have never seen one eat. Now, telescopes have provided the closest look yet at gas spiraling toward a feeding frenzy at the heart of a turbulent galaxy. The process, described here 9 January at a meeting of the American Astronomical Society, may fuel the outbursts of energy that rage inside all active galaxies.
Black holes and their surroundings are far too compact for telescopes to resolve. The best astronomers can do is infer the presence of the holes by watching stars or gas revolve around them, like leaves caught in a whirlpool. Recently, a study at the European Southern Observatory (ESO) exposed what appeared to be streamers of gas channeling toward the center of an active spiral galaxy called NGC 1097, about 47 million light-years away. However, the ESO astronomers did not measure the motions of the gas.
The new study charted those motions and tracked them within regions 10 times closer to the black hole than astronomers had managed for any other galaxy. Astronomer Kambiz Fathi of the Rochester Institute of Technology in New York and his colleagues used the 8-meter Gemini South Telescope at Cerro Pachón, Chile, to peer within 30 light-years of NGC 1097's core. A new instrument called an integral field spectrograph divided the light into several thousand individual points, each of which revealed the speed and direction of the swirling matter. The motions showed that the gas whirls at about 180,000 kilometers per hour--consistent with predictions for the neighborhood of a giant black hole--and relentlessly spirals inward.
The team then used sharp images from the Hubble Space Telescope to follow the gas even closer, within 10 light-years of the center. By extrapolating those tight motions toward the center, Fathi says, the team calculated that the gas will complete its "death spiral" in 200,000 years--a cosmic eyeblink of time.
Theorists had suggested that gaseous bars or rings of stars deep inside galaxies might block gas from penetrating all the way in, notes astronomer Kimberly Weaver of NASA's Goddard Space Flight Center in Greenbelt, Maryland. If that were true, then black holes would have difficulty gaining mass over time. The new analysis is a "major leap forward" to erasing that barrier, Weaver says: "These high velocities are a clear way to fuel the black hole and create the energies we see."