Science Journal -- Summer 2001 --Researchers Hear Whisper of Black Holes

Researchers Utilize Chandra for Record Observation, Hear Whisper of Black Holes

For the first time, astronomers believe they have proof black holes of all sizes once ruled the universe. NASA’s Chandra X-ray Observatory provided the deepest X-ray images ever recorded, and those pictures delivered a novel look at the past 12 billion years of black holes.

Two independent teams of astronomers presented images that contain the faintest X-ray sources ever detected, which include an abundance of active super-massive black holes.

The Penn State team made an historic one-million-second observation of X-rays coming from of an area of the sky near the Big Dipper.

That area of sky is now the most intensively surveyed by two of NASA’s Great Observatories: the Hubble Space Telescope, which detects visible light, and the Chandra X-ray Observatory, which detects X-rays.

The team has revealed new information about the X-ray glow that pervades the sky. Previously X-rays from only massive black holes—the brightest and loudest contributors—could be observed, but the team now has revealed small and very distant black holes only a few times the mass of our Sun, whose dim X-ray emissions are the equivalent of only a whisper.

“For the first time, we are able to use X-rays to look back to a time when normal galaxies were several billion years younger,” said Ann Hornschemeier, a Penn State graduate student who presented the team’s results during a televised NASA news conference.

The Penn State team’s research included a 500,000-second exposure in the Hubble Deep Field North and an additional 500,000 seconds of data, creating another one-million-second Chandra Deep Field, located in the constellation of Ursa Major.

“The Chandra data show us that giant black holes were much more active in the past than at present,” said Riccardo Giacconi, of Johns Hopkins University and Associated Universities, Inc., Washington, D.C.

The exposure is known as “Chandra Deep Field South” since it is located in the Southern Hemisphere constellation of Fornax. “In this million-second image, we also detect relatively faint X-ray emission from galaxies, groups, and clusters of galaxies.”

The images, known as Chandra Deep Fields, were obtained during many long exposures over the course of more than a year.

Data from the Chandra Deep Field South will be placed in a public archive for scientists.

“In essence, it is like seeing galaxies similar to our own Milky Way at much earlier times in their lives,” Hornschemeier added. “These data will help scientists better understand star formation and how stellar-sized black holes evolve.”

Combining infrared and X-ray observations, the Penn State team also found veils of dust and gas are common around young black holes.

Another discovery to emerge from the Chandra Deep Field South is the detection of an extremely distant X-ray quasar, shrouded in gas and dust.

“The discovery of this object, some 12 billion light years away, is key to understanding how dense clouds of gas form galaxies, with massive black holes at their centers,” said Colin Norman of Johns Hopkins University.

The Chandra Deep Field South results were complemented by the extensive use of deep optical observations supplied by the European Southern Observatory in Garching, Germany.

Hornschemeier’s work is supported, in part, by a NASA Graduate Student Researcher Program fellowship.

About Chandra Artist's rendering of Chandra

Chandra's Advanced CCD Imaging Spectrometer (ACIS) was conceived and developed for NASA by Penn State and Massachusetts Institute of Technology under the leadership of Penn State professor Gordon Garmire. The ACIS detector is a sophisticated version of the CCD detectors commonly used in digital cameras or video cameras.

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. TRW, Inc., of Redondo Beach, California, is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Massachusetts.

Chandra carries an X-ray telescope to focus the X-rays from objects in the sky. An X-ray telescope cannot work on the ground because X-rays are absorbed by the Earth's atmosphere. The Chandra X-ray Observatory is the third of NASA's Great Observatories, following the Hubble Space Telescope and the Compton Gamma-Ray Observatory. More information is available at http://chandra.harvard.edu and http://chandra.nasa.gov.

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