Oct. 26, 2007 -- A study of ancient galaxies led astronomers to a gold mine of black holes, a discovery that more than doubles the number of these phenomena found in the early universe.
"We had seen the tip of the iceberg. Now, we can see the iceberg itself," said Mark Dickinson, with the National Optical Astronomy Observatory in Tucson, Ariz.
Astronomers discovered that active, supermassive black holes were ubiquitous in the early universe, though they are difficult to observe. Black holes are objects so dense that not even light can escape the grasp of their massive gravitational fists.
They are detected by studying their effects on nearby objects and matter. Scientists using a pair of complementary space telescopes -- one sensitive to X-ray radiation and the other probing infrared wavelengths -- discovered the black holes hiding deep inside envelopes of dust and gas that pocket ancient galaxies.
The tell-tale sign was an unusually large amount of infrared radiation due to the black holes' heating of surrounding dust. The doughnut-shaped structures that comprise the ancient black holes and dust clouds are called quasars and they typically emit X-rays as the black hole cores devour their dusty rings.
The infrared radiation was a clue that something else was going on.
Scientists initially were studying 1,000 galaxies formed when the universe was between 2.5 and 4.5 billion years old. The galaxies were believed to be without the black hole-laced quasars. Observations with the Spitzer infrared telescope, however, revealed about 200 of the galaxies were radiating an unusual amount of infrared light.
When combined with X-ray images from the Chandra observatory, astronomers found that the galaxies were hiding quasars inside. Previously only a handful of the most energetic quasars were found in ancient structures.
"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 team of researchers.
The scientists estimate the number of black holes found to be in the hundreds of millions.
The findings, which will be published in the Nov. 10 issue of the Astrophysical Journal, are helping astronomers understand how the first galaxies in the universe formed. Among the realizations: stars and black holes built up simultaneously until the black holes got so big that they suppressed star formation.
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