Astronomers find ancient galaxy

March 16, 2002 at 12:16 PM
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HONOLULU, March 15 (UPI) -- Astronomers have found a galaxy they figure was formed about 780 million years after the birth of the universe, tagging the galaxy as the oldest object found yet.

The galaxy is about 50 million years older than the previous record-holder -- a quasar, or quasi-stellar object, which is an extremely luminous distant object believed to be powered by a black hole.

"Scaling the age of the universe to a person's lifetime, we're showing you baby pictures," said University of Hawaii researcher Esther Hu. "The last galaxy snapshot showed a toddler just past his fourth birthday. This one is 3 1/2."

Scientists believe the universe was born 14 billion to 16 billion years ago in a massive explosion called the Big Bang. During the next 500 million years, the universe expanded and cooled, allowing glowing plasma to recombine into hydrogen and helium. The telltale sign of this stage of the universe's development is the cosmic microwave background radiation, which scientists have used to map the general shape of the universe.

The next phase, called the Dark Ages, began as the gas began to coalesce into the first galaxies. That period, also lasting about 500 million years, ended when radiation emitted by the newly formed galaxies and quasars re-energized surrounding gases, allowing the first light of the universe to seep out.

"At some point a billion or so years after the Big Bang, gravitational attraction caused the gas that filled the universe to collapse and form the first stars. Searching for signs of those stars is one of the most interesting challenges in modern astronomy," said astronomer Richard Ellis of the California Institute of Technology.

To catch a glimpse of a primordial galaxy, which is far fainter than a quasar, scientists look for a particular chemical fingerprint in light that is associated with hydrogen.

Hu and her team used a filter on the massive Keck telescope, which has a primary mirror more than three times the size of the Hubble Space Telescope, to detect the hydrogen-tainted radiation. They also used a naturally occurring magnifying lens in space to boost the Keck's observing power.

The so-called gravitational lenses are caused by galaxy clusters between Earth and the more distant objects. The clusters' gravity is so great that it bends transversing light waves, causing a distortion and in some cases a magnification of that more distant light.

Hu's team used a galaxy cluster called Abell 370, which is about 6 million light years from Earth, to magnify light from a galaxy behind the cluster that is estimated to be 15.5 billion years old.

The finding was verified by infrared images from Hawaii's Subaru Telescope.

The discovery bodes well for the scientific harvest from NASA's planned Next Generation Space Telescope, which is being designed with the primary goal of imaging the universe's first residents.


(Written by Irene Brown at Cape Canaveral, Fla.)

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