The brightest lights in the universe have illuminated part of the life history of galaxies. Astronomers see hints that two distant quasars, beacons of energy powered by matter spiraling into gigantic black holes, are wrapped in cocoons of gas the size of our Milky Way. New gas plunges toward the cocoons at fantastic rates--fast enough to explain how black holes arose so quickly after the big bang.
The results could help close a big gap between theory and observation. Several quasars that shone when the universe was less than 1 billion years old have surfaced during the Sloan Digital Sky Survey, an ongoing census of the sky. The only way to make the quasars so bright, astronomers believe, is for supermassive black holes to devour gas at the hearts of large galaxies. So far, however, the most remote, ancient galaxies they can see have all seemed tiny--much smaller than our own mature galaxy of hundreds of billions of stars.
Now, two astrophysicists claim that Milky Way-sized shrouds of matter did indeed exist around quasars. Rennan Barkana of Tel Aviv University in Israel and Avi Loeb of Harvard University in Cambridge, Massachusetts, realized that the gravity of such shrouds should attract more gas at high rates, like water drawn into a whirlpool. Then, this new gas abruptly stops in a shock wave when it falls onto the growing galaxy. As the quasar's energy beams through this plunging gas, Barkana and Loeb calculated, the gas and the shock wave imprint a distinct pattern upon the spectrum of the quasar's light.
In the 23 January issue of Nature, the team describes two quasars that display this signature. The speeds of the gas imply that the shrouds gained up to 3000 times the mass of our sun each year--fast enough to build a supermassive black hole in just a few hundred million years. Although telescopes can't see the infant galaxies around the quasars, Loeb says they had to be at least as big as the Milky Way. "We're measuring the force of gravity that the host galaxy exerts on its surroundings," he says. "No other force can produce the infalling gas."
The evidence for young massive galaxies is the best yet, agrees astrophysicist Laura Ferrarese of Rutgers University in Piscataway, New Jersey. "It's encouraging when even a simple model can reproduce observations that have baffled people for a long time," she says. Still, she awaits data from other quasars to verify the research. Astronomers are using the Keck Telescopes in Hawaii to collect spectra from a few more distant quasars, Loeb notes.
Related sites
Avi Loeb's home
page
Sloan Digital Sky Survey
Papers
on how supermassive black holes formed
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