Image: NASA/CXC/PSU/N. BRANDT ET AL.
Astronomers have investigated the three most distant known quasars, located 13 billion light-years away from the earth. In the process, they observed radiation emitted when the universe was only one billion years old, a mere 7 percent of its present age. The findings may shed new light on the evolution of the brightest celestial objects in the universe.
The Sloan Digital Sky Survey discovered the quasars last year. In January of this year, astronomers used the Chandra X-ray Observatory to observe the triplets for three, two-hour-long periods. The researchers analyzing the data all determined that the black holes powering the x-rays are huge, considering the object's relative youth. Estimates place the weights of their central supermassive black holes between one and 10 billion times the mass of the sun. In comparison, the black hole at the center of the Milky Way is thought to be approximately three million times as massive as the sun.
Other observations, however, did not elicit agreement among all the astronomers inspecting the quasars. Some scientists concluded that the new quasars looked similar to those closer to the earth that are nearly twice their age, which may suggest that conditions around the central black hole did not change much over time. "These young quasars do not appear to be any different from their older cousins, based upon our current understanding and assumptions," says Smita Mathur of Ohio State University. "Perhaps the most remarkable thing about them may be that they are so absolutely unremarkable." A group led by Niel Brandt of Penn State University reached a similar conclusion.
Jill Bechtold of the University of Arizona and colleagues, in contrast, report that the three most distant quasars are in fact different than similar objects located closer to our planet. Her team compared the three Sloan quasars with 14 other quasars residing between 12 and 12.5 billion light-years away from the earth. They report that the more distant quasars were radiating a lower percentage of their energy in x-rays than were their older counterparts.
Determining just what is happening at the center of these quasi-stellar objects will require more research and perhaps more outings for Chandra. Brandt, for one, is optimistic. "These results," he says, "indicate that future x-ray surveys should be able to detect the first black holes to form in the universe."