Hundreds of Missing Black Holes Found

A team of astronomers has found hundreds of black holes hiding deep inside galaxies that are billions of light-years away. The massive, growing black holes represent a large fraction of a long-sought missing population. "The discovery implies that there are hundreds of millions of additional black holes growing in our young universe, which more than doubles the total amount known at that distance," said Penn State Professor of Astronomy and Astrophysics Niel Brandt, one of the scientists on the team who made the discovery with NASA's Spitzer and Chandra space telescopes. The findings, which are published in Astrophysical Journal, also are the first direct evidence that most, if not all, massive galaxies in the distant universe spent their youths building monstrous black holes at their cores.

Active black holes -- highly energetic structures with gravitational pulls so strong that not even light can escape -- give off X-rays that can be detected as a general glow in space. These shining objects, also called quasars, often cannot be seen because dust and gas block their X-rays from our view. But when Brandt and his colleagues peered more closely at the galaxies with Spitzer's infrared eyes, they noticed that about 200 of them gave off an unusual amount of infrared light. After analyzing the X-ray data from Chandra with a statistical technique called stacking analysis, they concluded that the galaxies contained quasars.

"We found most of the population of hidden quasars in the early universe," said Emanuele Daddi of the Commissariat a l'Energie Atomique in France, who led the research. Previously, only the rarest and most energetic of these hidden black holes had been seen.

At 9 to 11-billion light-years away, the galaxies observed by the scientists existed at a time when the universe was in its infancy. Therefore, the newfound quasars are helping to answer fundamental questions about how massive galaxies evolve. For instance, the scientists learned that young galaxies spend their youths building giant black holes at their cores. They also learned that most massive galaxies steadily build up their stars and black holes simultaneously until they get too big and their black holes suppress star formation.

"The combination of Spitzer and our deepest X-ray surveys, the Chandra Deep Fields, continues to yield fresh insights into black-hole growth," said Brandt. "I am amazed at the tremendous scientific mileage one can get from a well-executed deep survey of space beyond our Galaxy."

CONTACTS:

Neil Brandt: (+1) 814-865-3509, niel@astro.psu.edu
Barbara Kennedy (PIO): (+1) 814-863-4682, science@psu.edu