Press Release

The Most Distant Quasars Probe End of Cosmic Dark Ages

By SpaceRef Editor
February 14, 2004
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The most distant known quasars show that some supermassive black holes
formed when the universe was merely 6 percent of its current age, or about
700 million years after the big bang.

How black holes of several billion solar masses formed so rapidly in the
very early universe is one mystery raised by astronomers with the Sloan
Digital Sky Survey (SDSS). They have discovered 13 of the oldest, most
distant quasars yet found.

“We hope to at least double that number in the next three years,” said
Xiaohui Fan of the University of Arizona’s Steward Observatory in Tucson.

Fan led the SDSS team that discovered the distant quasars, which are compact
but luminous objects thought to be powered by supermassive black holes. The
most distant quasar, in the constellation Ursa Major, is roughly 13 billion
light years away.

The most ancient quasars raise other tantalizing questions about the early
universe. Fan talked about it today (Feb. 13) at the American Association
for the Advancement of Science annual meeting in Seattle.

The infant universe was hydrogen and helium.

“But we see a lot of other elements around those early quasars,” Fan said.
“We see evidence of carbon, nitrogen, iron and other elements, and it’s not
clear how these elements got there. There is as much iron, proportionate to
the population of those early systems, as there is in mature galaxies
nearby.”

Astronomers estimate the current age of the universe at 13.7 billion years.
Quasars in the early universe looked as mature as nearby galaxies that, like
the Milky Way, formed a couple of billion years after the big bang.

Also, radio astronomers collaborating with SDSS researchers detected carbon
monoxide, a key component of molecular clouds, near the ancient quasars.

All this evidence suggests that the first mature galaxies formed right along
with the ancient supermassive black holes in the very early universe.

Although cosmologists aren’t panicked, they need to refine theory to clarify
what’s going on.

Fan and his colleagues believe the oldest quasars can be used to probe the
end of the Cosmic Dark Ages and the beginning of the Cosmic Renaissance.
In so-called Cosmic Dark Ages, the universe was a cold, opaque place without
stars. Then came a critical phase where the universe when through a rapid
transition. The first galaxies and quasars formed in the Cosmic Renaissance,
heating the universe so it became the place we see today.

Fan and his colleagues believe some of their oldest known quasars may span
the critical transition.

“Our observations suggest that what we may be seeing during this transition
is atomic hydrogen becoming completely ionized. This ionization process was
one of the important processes going on during the first one billion years.”

Current observations have just begun to reveal when and how this ionization
process occurred. Data from distant quasars combined with other evidence,
such as from the cosmic microwave background, which is relict radiation from
the big bang, will begin to test theory of how the first galaxies appeared
in the universe, Fan said.

It may take the large-aperture space telescope, NASA’s 6.5-meter James Webb
Space Telescope, to really explore what happened between the Cosmic Dark
Ages and the Cosmic Renaissance, Fan said.

Optical/infrared ground-based telescopes cannot detect objects red-shifted
much beyond 6.5, Fan noted. Water vapor in Earth’s atmosphere absorbs longer
infrared wavelengths, so it will take a space-based telescope, probably with
an aperture larger than that of the NASA Spitzer Telescope now orbiting
Earth, to study objects at redshift 7, 8, or 10 in detail, Fan said.

(So-called redshift is a phenomenon proportional to the velocity of a a
celestial object speeding away from Earth. The lines in its spectrum shift
toward longer, red wavelengths. Astronomers now believe that the most
distant objects recede from Earth at the highest velocities, so the farther
away an object is, the greater its redishift.)

The Sloan Digital Survey will produce a detailed map of one-quarter of the
entire sky. The survey will map positions and absolute brightness of 100
million celestial objects, including about 100,000 quasars. For more about
SDSS, visit the Website http://www.sdss.org

SpaceRef staff editor.