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. Last Updated: 07/27/2016

X-Rays Give Peek at Cosmic Past

ATLANTA -- In a discovery that could help explain the origin of the earliest galaxies, a new astronomy satellite has detected the first discrete objects in the mysterious glow of X-rays that pervades the distant universe.

Some of the faintest of the radiation sources, astronomers said, could be the most distant objects ever observed. They promise to be important clues to conditions in the cosmic dark age, the period that began soon after the Big Bang created the universe and lasted until the emergence of a multitude of stars, perhaps a billion years.

Many of the X-rays appear to be emanating from the cores of galaxies. These cores, being seen now as they existed in the early universe, were probably supermassive black holes sucking in gas at nearly the speed of light and generating tremendous radiation. Yet in many cases, the objects do not emit visible light, suggesting that they existed at a time before the multitude of stars.

The discovery, reported in Atlanta on Jan. 13 at a meeting of the American Astronomical Society, was hailed by scientists as the first major step in solving the mystery of the pervasive X-rays that form a backdrop throughout the universe. Until the launching of NASA's Chandra X-ray Observatory five months ago, the mystery had defied explanation.

"We are all very excited by this finding," said the leader of the discovery team, Richard Mushotzky of the Goddard Space Flight Center in Greenbelt, Maryland. "These are signposts of the first things formed in the universe."

Other astronomers called it "a major discovery" and said the data appeared to be impressive, although they wanted to see more observations by the Chandra spacecraft, the Hubble Space Telescope, and ground-based telescopes, to understand the phenomenon fully.

"We are probing further and further into the past of galaxy formation and how that happened," said Virginia Trimble, an astronomer at the University of California at Irvine, who was not a member of the discovery team.

Discussing the implications of the findings at a news conference, Trimble said the objects showed for the first time what is creating the X-ray background in space and also revealed that this background radiation is not smooth but instead marked by subtle fluctuations.

That could give astronomers an opening for new investigations into one of the most fundamental unanswered questions in cosmology: How did matter created in the aftermath of the Big Bang, once all but uniformly smooth, get to be as lumpy as it is now in a universe of large-scale structures like galaxies and spreading clusters of galaxies?

Learning more about the X-ray objects, Trimble said, should give astronomers important insights into the transition, which must have occurred during the cosmic dark age, all but unobservable until now. The only earlier phenomenon previously observed was microwave background radiation, a relic of the Big Bang itself.

The new findings, however, along with other research reported at the astronomy meeting, suggest that relatively starless galaxies may have been emerging everywhere during the dark age.

In this interpretation, masses of gas and also dark matter, the exotic particles created by the Big Bang that are thought to be a major cosmic constituent, plumped together into proto-galaxies. At the cores of at least some, the masses were so great that they formed black holes, those awesome gravitational sinks so dense that, by the rules of Einstein's general theory of relativity, nothing, not even light, can escape them. As ravenous black holes consumed more gas, they produced the X-rays now being observed and marking the locations of those galactic cores.

If this interpretation is correct, then the X-ray observations suggest that galaxy formation and black holes preceded the period of star formation, a possibility raised by theorists in recently.

An article describing the X-ray discovery is to be published soon in the journal Nature by Mushotzky of Goddard and his collaborators: Lennox Cowie and Amy Barger of the University of Hawaii and Keith Arnaud of the University of Maryland.

The Chandra observatory, a 5,400-kilogram spacecraft in Earth orbit, was designed to examine X-ray sources much fainter and more distant than before. The newly described X-ray background was observed for almost 28 hours last month with the spacecraft's imaging spectrometer. The instrument was built for the National Aeronautics and Space Administration by the Massachusetts Institute of Technology and Pennsylvania State University.

Mushotzky's team looked at a small sector of the sky, a circle about one-fifth the size of a full moon. The researchers were able to resolve about 80 percent of the X-ray glow in that region into specific light sources. Extrapolated across the entire sky, this would add up to about 70 million sources, most of which are galaxies.