 
Newfound
quasar wins title "most distant in the universe,"
UC Berkeley and Caltech astronomers report
25
Feb 2000
By
Michelle Viotti and Robert Sanders, Public Affairs
BERKELEY--
If Guinness had a Book of Cosmic Records, a newly discovered
quasar in the constellation Cetus would make the front page.
This distant quasar easily skates past the previous record-holder,
placing it among the earliest known structures ever to form
in the universe.
A
team of astronomers identified the candidate after nights of
deep, long-exposure imaging at the California Institute of Technology's
five-meter (200-inch) Hale Telescope at Palomar Observatory
in California and at the National Science Foundation's four-meter
(157-inch) Mayall Telescope at Kitt Peak, Ariz. A spectral analysis
of the quasar's light was then completed at the 10-meter Keck
Observatory telescope in Hawaii.
"As
soon as we saw the spectrum, we knew we had something special,"
said Daniel Stern, an astronomer at NASA's Jet Propulsion Laboratory
in Pasadena, who played a key role in the discovery. "In
images, quasars can look very much like stars, but a spectral
analysis of a quasar's light reveals its true character. This
quasar told us that it was 'an ancient' - one of the universe's
first structures."
Quasars
are extremely luminous bodies that were more common in the early
universe. Packed into a volume roughly equal to our solar system,
a quasar emits an astonishing amount of energy - up to 10,000
times that of the whole Milky Way galaxy. Scientists believe
that quasars get their fuel from super-massive black holes that
eject enormous amounts of energy as they consume surrounding
matter.
"This
one is unusual in that it is emitting a lot of ultraviolet light,
considering how young it is," said Hyron Spinrad, professor
of astronomy at the University of California, Berkeley, and
the leader of the observing group. "It's less than a billion
years old, so it had to have grown its central black hole very
fast, faster than the one solar mass per year we estimate for
most quasars."
The
recent findings will be presented in an upcoming issue of the
Astrophysical Journal Letters. The paper was written by Stern
and Peter Eisenhardt of JPL; Spinrad and Steve Dawson of UC
Berkeley; Andrew Bunker of Cambridge University; Richard Elston
of the University of Florida; and Adam Stanford of UC Davis
and Lawrence Livermore National Laboratory.
A
quasar's "redshift" measures how fast the object is
moving away from us as the universe expands, and is a good indicator
of cosmic distances. The faster it moves away, the more its
light shifts to the red part of the spectrum (toward longer
wavelengths). The quasars ultraviolet emissions have been redshifted
into the far red part of the visible spectrum, almost into the
infrared.
Because
the faster an object appears to move, the farther away it is,
at a redshift of 5.5, light traveling from Stern's quasar has
journeyed about 13 billion years to get here. That means the
quasar existed at a time when the universe was less than 8 percent
of its current age.
"The
odds against us finding a quasar at a redshift of 5.5 were fairly
large, especially when you consider how small a portion of the
sky we were observing - 10 by 10 arcminutes. To get an idea
of how small that is, try holding a dime at arms-length against
the night sky; it's roughly the size of FDR's ear," said
Stern. Until the last few years, no one had discovered an object
that came close to a redshift of 5.0.
High-redshift
quasars are vitally important to understanding one of the biggest
mysteries confronting scientists: how the universe went from
the smooth uniformity of its youth to the clumpy, galaxy-strewn
formations we observe today. Astronomers believe that the young
universe began in a hot, dense state shortly after the Big Bang.
Matter in the universe was ionized back then, meaning that electrons
were not bound to protons. As the universe aged, matter cooled
enough for electrons and protons to combine, or to become neutral.
As the first stars and galaxies formed, they reheated matter
between galaxies, creating the ionized intergalactic medium
we see today in our local universe. The million-dollar question
for today's cosmologists is when this second transition from
neutral to ionized gas occurred.
Analyzing
the spectrum of the new quasar will be very useful for testing
whether the universe was neutral or ionized at redshift 5.5.
As a quasar's light makes its journey toward us, the light is
absorbed by any matter that lies in its path. Scientists have
learned that clouds of neutral hydrogen absorb more than half
of a quasar's light at high redshift (in the early universe).
That finding is central to understanding when and how super-massive
black holes, quasars and other structures condensed from large,
high-density clouds of hydrogen soon after the Big Bang. The
new quasar will also shed light on how matter was distributed
at earlier stages of cosmic history.
"Finding
a quasar at this distance is like turning on a flashlight at
the edge of the universe," said Stern. "Because quasars
are more luminous than distant galaxies at the same redshift,
they act as the brightest flashlights, allowing us to study
everything that has ever developed between us and the quasar."
The
W.M. Keck Observatory, atop Mauna Kea on the island of Hawaii,
is managed by a partnership among Caltech, the University of
California and NASA. JPL is a division of Caltech, Pasadena,
Calif. The Palomar Observatory, near San Diego, Calif., is owned
and operated by Caltech. Kitt Peak National Observatory is a
division of the National Optical Astronomy Observatory (NOAO),
which is operated by the Association of Universities for Research
in Astronomy, Inc., under Cooperative Agreement with the National
Science Foundation.
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