Chandra discovers black holes in distant quasars
Posted: March 29, 2002

Pushing further back toward the first generation of objects to form in the Universe, NASA's Chandra X-ray Observatory has observed the three most distant known quasars and found them to be prodigious producers of X-rays. This indicates that the supermassive black holes powering them were already in place when the Universe was only about one billion years old.

The three quasars. Credit: NASA/CXC/PSU/N.Brandt et al.
"Chandra's superb sensitivity has allowed the detection of X-rays from the dawn of the modern Universe, when the first massive black holes and galaxies were forming," said Niel Brandt of Penn State University, leader of one the teams involved. "These results indicate that future X-ray surveys should be able to detect the first black holes to form in the Universe."

The three quasars were recently discovered at optical wavelengths by the Sloan Digital Sky Survey and are 13 billion light years from Earth, making them the most distant known quasars. The X-rays Chandra detected were emitted when the Universe was only a billion years old, about 7 percent of the present age of the Universe.

Since X-rays reveal conditions in the immediate vicinity of supermassive black holes, Brandt proposed that Chandra look at these objects in three snapshots of about two hours each to see if they were different from their older counterparts. The observations on January 29, 2002 were made public immediately and the four different teams quickly went to work on them.

Brandt's team concluded that the quasars looked similar to ones that were at least twice as old, so the conditions around the central black hole had not changed much in that time, contrary to some theoretical expectations. A team led by Smita Mathur of Ohio State University reached a similar conclusion.

"These young quasars do not appear to be any different from their older cousins, based upon our current understanding and assumptions," said Mathur. "Perhaps the most remarkable thing about them may be that they are so absolutely unremarkable."

Jill Bechtold of the University of Arizona and her colleagues disagree. In addition to the three distant Sloan quasars, they observed 14 other quasars with distances between 12 and 12.5 billion light years. Bechtold's group looked at their larger sample to determine that the younger, more distant quasars were radiating a lower percentage of their energy in X-rays.

"The X-ray data are consistent with predictions of some theories that a hot gas atmosphere is associated with the accretion disk swirling around a central supermassive black hole," said Bechtold, provided the distant quasars have more massive black holes than nearby ones. "These theories predict that large supermassive black holes should be relatively weaker X-ray emittters than smaller ones, which is what we observed with Chandra.

All groups agreed that the masses of the black holes producing the X-rays are huge, given their relative youth. By various estimates, the three quasars each weighed in at between one and 10 billion times the mass of the Sun. By comparison, the black hole at the center of the Milky Way is believed to contain the mass equivalent to only about 3 million Suns.

Daniel Schwartz of the Harvard-Smithsonian Center for Astrophysics took a different approach to the same data. In addition to looking at the quasars themselves, he examined the space around them. His search paid off with the discovery of a new X-ray source, which may be only about half a million light years away from the quasar SDSS 1306+0356

"It's not clear what the source is," said Schwartz. "One plausible explanation is that it is due to a high energy jet of material ejected by the quasar over at least several hundred thousand years." Chandra has detected a number of such jets, which could be generated by the extraction of energy from the rotation of a supermassive black hole.

In addition to SDSS 1306+0356, which has a cosmological redshift z = 5.99, the other distant Sloan Digital Sky Survey quasars observed in this study are SDSS 0836+0054 (redshift z = 5.82) and SDSS 1030+0524 (redshift z=6.28). The paper from Brandt et al has been published in The Astrophysical Journal Letters, and Mathur et al and Schwartz et al will have in separate papers appearing shortly in same publication; the work of Bechtold et al will be published in The Astrophysical Journal.

These observations were made with Chandra's Advanced CCD Imaging Spectrometer, which was conceived and developed for NASA by Penn State and the Massachusetts Institute of Technology. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.