- ATLANTA - The newly witnessed
demise of a galaxy has given astronomers a glimpse into the lives and deaths
of spiral galaxies in a violent universe, and possibly a view of the ultimate
fate of the Milky Way.
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- Once like the Milky Way, the ill-fated spiral galaxy
C153 ripped through the heart of a distant galactic cluster at 4.5 million
mph (2,012 kilometers per second), being shredded along the way. As the
galaxy careens away from the cosmic collision, gas trails in streams 200,000
light-years long.
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- "Its entry into the cluster has created the perfect
storm," explained astronomer William Keel, of the University of Alabama,
of C153. The destruction is happening "all at once, instead of spread
out over a billion years."
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- Other galactic collisions typically involve partial distortion
of one or both galaxies as a long, orbiting dance ensues. This was a head-on
collision.
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- Keel and a team of researchers studied the C153 smash-up
as part of a broader investigation into spiral galaxies. According to past
observations, rich galactic clusters in the early universe were flush with
spiral galaxies, only to have numbers diminish as time progressed. Consumption
by those clusters during an errant collision, astronomers say, may explain
the cosmic evolution.
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- "Its a very visual thing, this transformation of
galaxies," Keel said. "But it has been difficult to see because
clusters are such busy environments, with so many things happening at once."
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- Keel and his colleague, Daniel Wang from the University
of Massachusetts, announced their research here today at a meeting of the
American Astronomical Society. Astronomers Frazier Owen, of the National
Radio Astronomy Observatory, and Michael Ledlow at the Gemini Observatory
also participated in the study.
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- Death plunge
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- Using optical, x-ray and radio telescopes, Keel and his
colleagues were able to deconstruct the death plunge of C153 as it is stripped
of its gas by the collision, leaving only its skeletal spiral arms in place.
The free gas, however, is being put to work making new stars in the core
of the galactic cluster, dubbed Abell 2125, which sits about three billion
light-years from Earth.
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- Keel's team first noticed the doom of C153 while studying
Abell 2125 in the 1990s. Researchers were using the Very Large Array radio
telescope near Socorro, New Mexico when they detected the unusually high
population of radio galaxies in Abell 2125. The spiral C153, it turned
out, was among the post powerful of those galaxies.
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- "Its the brightest compact galaxy in the entire
cluster," said Wang, who used NASA 's orbiting Chandra X-ray Observatory
to study the stream of gas being stripped from C153. "In 100 million
years or so, though, it will lose all its gas in the collision."
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- Hubble Space Telescope observations of C153 showed a
clumpy object with a large number of young stars and chaotic dust formations.
Besides disruptions in the galaxys disk, Hubble images showed signs of
recent star formation in the wake of the galaxy, as well as along the leading
edge of C153, where some gas is compressed into stellar birth.
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- But the majority of available gas is being blown back
like the air around a speeding car, Wang said.
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- Eventually, the galaxy will lose the last trappings of
its spiral arms, with only a central bulge and disk to hint at its previous
spiral-armed existence. Such galaxies are common in dense galactic clusters
seen today. Keel and his team hope to make more observations of C153s tail
structure later this year to study the dynamics of gas and stars in the
trailing tail.
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- Our own fate?
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- The death of C153 provided astronomers one possible future
for our Milky Way galaxy as it moves through its own galactic neighborhood,
the Virgo cluster. While the galaxy is still in the outskirts of the Virgo
Cluster, it could plummet into the cluster in 50 to 80 billion years time.
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- "The Milky Way has been very lucky," Wang said.
"It still is in the [cosmic] suburbs or countryside."
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- Other studies indicate the Milky Way is headed for an
eventual collision with the Andromeda Galaxy, another large spiral. Computer
models indicate that crash will result in a merger of the two galaxies.
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