Astronomers have long assumed that quasars are among the farthest
and fastest moving objects in the universe.
Their belief is based on the fact that
the light spectra from quasars—intensely bright objects produced
by superheated gas and dust swirling into a black hole—often
exhibit what astronomers call a high “red shift,” a measure
of the speed at which an object is receding from Earth.
But Professors Margaret and Geoffrey Burbidge at UCSD’s
Center for Astrophysics and Space Sciences have found compelling
evidence
within a nearby galaxy to question that longstanding assumption.
In
a paper published in the Astrophysical Journal, they report their
discovery of a quasar whose light spectrum suggests
that it is billions of light years away.
Their finding presents a cosmic
conundrum: How could a galaxy 300 million light years away contain
a stellar object several billion
light years away? (A light year, the distance it takes light to travel
in a year, is nearly six trillion miles.)
“Most people have wanted to argue that quasars are right at the edge
of the universe,” says Geoffrey Burbidge. “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.”
The UCSD discovery is significant because it is the most extreme
example of a supposedly “distant” quasar associated with
a nearby galaxy. 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 from a moving train becomes lower in
pitch, or sound frequency, as the train travels away.
Astronomers have used red shifts and the known brightness of stars
as fundamental yardsticks to measure the distances to stars and
galaxies. But Burbidge says they have been unable thus far to account
for the
growing number of quasars with high red shifts that have been closely
associated with nearby galaxies.
“If it weren’t for this red-shift dilemma, astronomers would
have thought quasars originated from these galaxies or were fired
out from them like bullets or cannon balls,” he quips.
“If this quasar is close by, its red shift 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.” Stay tuned. The debate
is just beginning to heat up.
— Kim McDonald
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