Galaxy goes on the black hole diet

The latest X-ray view of a photogenic galaxy shows that the feeding habits of black holes are the same, whether they're 10 times or 70 million times as massive as the sun.

Black holes are thought to come in all sizes, from supermicro proton-size to supermassive galaxy-size. But are all black holes alike? Albert Einstein thought so: General relativity suggests that the collapsed singularities are simple things, varying only in how big they are and how much they spin.

Some astronomers have taken issue with Einstein, however. Stellar-mass black holes are in settings that are much different from galaxy-scale black holes, which might lead to differences in diet and behavior: The smaller ones suck in whirling disks of gas from their companion stars, while the bigger ones feed on the material surrounding them at the dense cores of galaxies.

In an effort to shed new light on a black hole's digestive routine, astronomers observed the spiral galaxy M81, about 12 million light-years from Earth, using NASA's Chandra X-Ray Observatory as well as three radio-telescope arrays, two millimeter-wave telescope arrays and the infrared camera at the Lick Observatory.

In a paper due to appear in The Astrophysical Journal, the international research team reports that M81's monster black hole behaves much the same as stellar-mass suckers, in their pattern of activity as well as in the distribution of radiation given off as whipped-up material falls into the singularity.

"This confirms that the feeding patterns for black holes of different sizes can be very similar," Sera Markoff of the University of Amsterdam's Astronomical Institute, the leader of the study, said in a Chandra news release. "We thought this was the case, but up until now we haven't been able to nail it."

The study confirms earlier work by Andrea Merloni of Germany's Max Planck Institute for Extraterrestrial Physics and his colleagues: The new model fleshes out the details, using more detailed observations made simultaneously by different telescopes.

X-ray emissions are the hallmark of a black hole's activity, which is why the Chandra observations were key to the latest study. Other wavelengths show up to varying degrees in different regions around the black hole (which emits no radiation on its own):

• A thin disk of material swirling around the singularity shows up in visible light and X-rays.
• A region of hot gas emits ultraviolet and X-ray light.
• The top and bottom jets generated by a black hole produces radio waves and X-rays.

"When we look at the data, it turns out that our model works just as well for the giant black hole in M81 as it does for the smaller guys," said the Massachusetts Institute of Technology's Michael Nowak, a co-author of the study. "Everything around this huge black hole looks just the same, except it's almost 10 million times bigger."

If astronomers confirm that the model holds true for all black holes, that could help them confirm the existence of a mysterious intermediate class of black holes. Some candidates for the midsize class have already been identified, but researchers are debating whether they're actually black holes or examples of other cosmic phenomena. Closer observations could reveal whether the objects are following the required black hole diet.

If you're dying to beef up the black-hole content in your information diet, check out these archived stories on the subject - including reports that let you listen to a black hole's emissions and even tell you the key of a black hole's song. And if it's glittering views of the M81 galaxy you're looking for, we've got those too.