Contact:
Christopher Wanjek
wanjek@gsfc.nasa.gov
301-286-4453

June 4, 2002

Albuquerque, N.M. -- Scientists have found the faintest X-ray sources yet to be detected in the early universe, extremely distant galaxies that may include the first X-ray binary star systems to form, or perhaps nascent black holes that ultimately merge and grow into supermassive black holes.

A team from Carnegie Mellon University in Pittsburgh and the European Space Technology Center in The Netherlands uncovered the sources with NASA's Chandra X-ray Observatory and ESA's XMM-Newton satellite. The scientists used a novel technique called fluctuation analysis that allowed them to observe sources ten times fainter than those revealed in previous analysis in this same region of the sky.

Team member Richard Griffiths, a professor of astrophysics at Carnegie Mellon, discusses the finding today at a press briefing at the American Astronomical Society meeting in Albuquerque, New Mexico, marking the 40th anniversary of X-ray astronomy.

Griffiths will also present a scientific paper at the meeting, co-authored by Takamitsu Miyaji, a research scientist at Carnegie Mellon, and David Lumb of the European Space Agency.

"The faint galaxies now being detected in X-rays using large X-ray telescopes in space are about ten billion times fainter than the first X-ray binary star discovered in 1962," said Griffiths. "We've come a long way in forty years."

The new X-ray sources detected are unique in several ways. In general, most of the X-ray glow from the depths of space comes from the activity of massive black holes at the centers of very distant galaxies, typically ten or twelve billion light years away. This latest observation, however, finds galaxies with X-ray sources outside of the core region.

The new sources, some closer than the massive black holes, are too dim to contribute much to the overall X-ray glow in the universe, called the X-ray background. Yet the sources may allow scientists to better understand the rate of star formation in the early universe.

The sources, Griffiths said, are likely galaxies containing hundreds of binary star systems in which one massive star orbits together with a compact object, such as a neutron star or stellar-size black hole, both of which form from the collapse of massive stars. Some systems may be intermediate-size black holes, which would contain the mass of tens to thousands of suns.

In the latter scenario, these compact objects, which scientists call ultraluminous X-ray sources (for it is not certain that they are indeed black holes), may sink to the center of galaxies and merge with other black holes over the course of billions of years. Thus, these objects now seen in the distant universe may be the building blocks of supermassive black holes, residing in the cores of most galaxies.

The new observation may eventually provide insight into the history of star formation in distant galaxies, for X-ray brightness is an indicator of star formation rate, and this is not affected by absorption due to dust. Much of the ultraviolet and visible light in the early universe is blocked by dust.

Thus, this new finding complements optical and ultraviolet data gathered with the Hubble Space Telescope, in particular, and by other telescopes on the ground. Chandra and XMM-Newton, the latest generation of X-ray telescopes, have the angular resolution and light-collecting capability to reveal structure that other telescopes cannot see -- particularly the more violent aspects of star formation that reveal themselves strongly as dust-penetrating X-ray radiation.

This new finding is complementary to optical and ultraviolet data that is being gathered with the Hubble Space Telescope. Just as Hubble¹s new advanced camera for surveys is using visible light to probe star formation in the early universe, so the new X-ray telescopes are being used to explore this epoch of violent star formation in the light of X-rays.