European scientists have used a "virtual observatory" to find 30 powerful supermassive black holes that previously escaped detection. These results, the first scientific discovery entirely from such an observatory, suggest that astronomers have underestimated the number of these "hidden" black holes by as much as a factor of 5.
Billions of times more massive than their run-of-the-mill brethren, supermassive black holes nestle at the hearts of so-called active galaxies, where their intense gravity sucks in matter and converts it into searing beacons of energy. Astronomers avidly study them for clues to galactic evolution. Unfortunately, the black holes also attract spiraling rings of dust that, when seen edge-on, block astronomers' view of the galactic core. Such black holes are known as type 2 sources, and many of them have been found in our neck of the universe. A handful of high-powered type 2 sources--emitting roughly 100 billion times the power of the sun--have also turned up much farther away. But until recently, astronomers assumed these supermassive black holes were rare.
In the latest search, researchers probed the so-called GOODS fields, the best-studied patches of sky, using Europe's 2-year-old Astrophysical Virtual Observatory, which gathers and analyzes data from the Hubble Space Telescope, the European Southern Observatory (ESO's) Very Large Telescope, NASA's Chandra X-ray Observatory, and other instruments. Each telescope on its own had spotted lone features of high-powered type 2 sources, such as high x-ray output or scant emissions of visible light; pooling the observations revealed what appear to be 30 new high-powered type 2 sources. Until now, only nine had been seen in GOODS fields and at most 10 to 20 elsewhere.
Astronomer Paolo Padovani of ESO at Munich and GOODS co-investigator said his team's discovery means that prior surveys might have underestimated the number of powerful supermassive black holes by two to five times. His team caught more of them, he suggests, because it looked at sources much dimmer in the visible spectrum. The findings could help researchers understand the black holes in galactic cores and likely how galaxies formed around these black holes, Padovani says. The findings will appear in Astronomy & Astrophysics.
"There have been few clear demonstrations of virtual observatory tools in research until now," says GOODS Space Infrared Telescope Facility researcher Mark Dickinson, an astronomer at the National Optical Astronomy Observatory in Tucson who did not participate in the current study. The new findings should encourage more astronomers to use such tools for their work, he says.