http://ucsdnews.ucsd.edu/newsrel/science/mcquasar.asp
January 10, 2005
Discovery By UCSD Astronomers Poses A Cosmic Puzzle:
Can A 'Distant' Quasar Lie Within A Nearby Galaxy?
By Kim McDonald
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.
Comment: Geoffrey Burbidge, (858) 534-6626
Media Contact: Kim McDonald (858) 534-7572