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2005-01-20
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Discovery Poses Cosmic Puzzle: Can A 'Distant' Quasar Lie
Within A Nearby Galaxy?
An international team of astronomers has
discovered within the heart of a nearby spiral galaxy a quasar
whose light spectrum indicates that it is billions of light
years away. The finding poses a cosmic puzzle: How could a
galaxy 300 million light years away contain a stellar object
several billion light years away?
The team’s findings, which were presented today in San Diego
at the January meeting of the American Astronomical Society and
which will appear in the February 10 issue of the Astrophysical
Journal, raise a fundamental problem for astronomers who had
long assumed that the “high redshifts” in the light spectra of
quasars meant these objects were among the fastest receding
objects in the universe and, therefore, billions of light years
away.
“Most people have wanted to argue that quasars are right at
the edge of the universe,” said Geoffrey Burbidge, a professor
of physics and astronomer at the University of California at San
Diego’s Center for Astrophysics and Space Sciences and a member
of the team. “But too many of them are being found closely
associated with nearby, active galaxies for this to be
accidental. If this quasar is physically associated with this
galaxy, it must be close by.”
Astronomers generally estimate the distances to stellar
objects by the speed with which they are receding from the earth.
That recession velocity is calculated by measuring the amount
the star’s light spectra is shifted to the lower frequency, or
red end, of the light spectrum. This physical phenomenon, known
as the Doppler Effect, can be experienced by someone standing
near train tracks when the whistle or engine sounds from a
moving train becomes lower in pitch, or sound frequency, as the
train travels past.
Astronomers have used redshifts and the known brightness of
stars as fundamental yardsticks to measure the distances to
stars and galaxies. However, Burbidge said they have been unable
to account for the growing number of quasi-stellar objects, or
quasars—intense concentrations of energy believed to be produced
by the swirling gas and dust surrounding massive black holes—with
high redshifts that have been closely associated with nearby
galaxies.
“If it weren’t for this redshift dilemma, astronomers would
have thought quasars originated from these galaxies or were
fired out from them like bullets or cannon balls,” he added.
The discovery reported by the team of astronomers, which
includes his spouse, E. Margaret Burbidge, another noted
astronomer and professor of physics at UCSD, is especially
significant because it is the most extreme example of a quasar
with a very large redshift in a nearby galaxy.
“No one has found a quasar with such a high redshift, with a
redshift of 2.11, so close to the center of an active galaxy,”
said Geoffrey Burbidge.
Margaret Burbidge, who reported the team’s finding at the
meeting, said the quasar was first detected by the ROSAT X-ray
satellite operated by the Max-Planck Institute for Astrophysics
in Garching, Germany and found to be closely associated with the
nucleus of the spiral galaxy NGC 7319. That galaxy is unusual
because it lies in a group of interacting galaxies called
Stephan’s Quintet.
Using a three-meter telescope operated by the University of
California at Lick Observatory in the mountains above San Jose
and the university’s 10-meter Keck I telescope on Mauna Kea in
Hawaii, she and her team measured the redshifts of the spiral
galaxy and quasar and found that the quasar appears to be
interacting with the interstellar gas within the galaxy.
Because quasars and black holes are generally found within
the most energetic parts of galaxies, their centers, the
astronomers are further persuaded that this particular quasar
resides within this spiral galaxy. Geoffrey Burbidge added that
the fact that the quasar is so close to the center of this
galaxy, only 8 arc seconds from the nucleus, and does not appear
to be shrouded in any way by interstellar gas make it highly
unlikely that the quasar lies far behind the galaxy, its light
shining through the galaxy near its center by “an accident of
projection.”
“If this quasar is close by, its redshift cannot be due to
the expansion of the universe,” he adds. “If this is the case,
this discovery casts doubt on the whole idea that quasars are
very far away and can be used to do cosmology.”
Other members of the team, besides Geoffrey and Margaret
Burbidge, included Vesa Junkkarinen, a research physicist at
UCSD; Pasquale Galianni of the University of Lecce in Italy; and
Halton Arp and Stefano Zibetti of the Max-Planck Institute for
Astrophysics in Garching, Germany.
Editor's Note: The original news release can be found
here.
This story has been adapted from a news release issued by
University Of California At San Diego.
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