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GALACTIC MERGER TO 'EVICT' SUN AND EARTH



 
 
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Old May 15th 07, 08:16 AM posted to soc.culture.indian,alt.fan.jai-maharaj,alt.jyotish,sci.physics,sci.astro
Dr. Jai Maharaj[_9_]
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Default GALACTIC MERGER TO 'EVICT' SUN AND EARTH

Galactic merger to 'evict' Sun and Earth

By Hazel Muir
NewScientist.com news service
Monday, May 14, 2007

It's hard to know where you'll be in five years' time,
never mind 5 billion. But astronomers have it all figured
out. In 5 billion years, they say, the Sun and Earth --
along with our atomic remains and any living Earthlings --
will inhabit "Milkomeda", the wreckage of a violent
collision between the Milky Way and the giant Andromeda
galaxy.

Now a new study has simulated the crash and asked: where
will the Sun end up in this mammoth galactic union? "We're
living in the suburbs of the Milky Way right now, but we're
likely to move much farther out after the coming cosmic
smash-up," concludes T J Cox from the Harvard-Smithsonian
Center for Astrophysics (CfA) in Cambridge, Massachusetts,
US.

[Caption] In less than 2 billion years, well within the
Sun's lifetime, the Milky Way and Andromeda (above) will
pass close to each other. Then they will overshoot and come
together again for a second close passage before finally
merging about 5 billion years from now. The merged galaxy,
dubbed Milkomeda, will be a blobby elliptical galaxy,
rather than a neat spiral like Andromeda or the Milky Way
today (Image: W Schoening/V Harvey/REU/NOAO/AURA/NSF)

The Milky Way belongs to a group of about 40 galaxies that
mill around in our cosmic neighbourhood, bound together by
their mutual gravitational pull. The two largest by far are
the Milky Way and Andromeda, a swirling spiral
http://space.newscientist.com/article/dn9282
of a trillion stars that lies about 2.5 million light years
away.

These two galaxies are currently rushing towards each other
at about 120 kilometres per second and will likely collide
in future. Now Cox and his CfA colleague Avi Loeb have run
computer simulations of this collision, using 2.6 million
particles to model the matter in both galaxies and in
intergalactic space. They accounted for the unidentified
invisible "dark matter" known to exist in space as well as
the ordinary matter in stars and clouds of gas.

Jump ship

The scientists watched how gravity choreographed the
motions of the two galaxies up to 10 billion years into the
future. The results suggest they will pass close to each
other in less than 2 billion years, well within the Sun's
lifetime. At this point, their mutual gravity would start
to mess up their structures and tug out long tails of stars
and gas.

The two galaxies would then overshoot and come together
again for a second close passage before finally merging
about 5 billion years from now. The merged galaxy, which
Loeb dubs Milkomeda, will be a blobby elliptical galaxy,
rather than a neat spiral like Andromeda or the Milky Way
today.

The Sun will almost certainly hang onto its clutch of
planets throughout the mayhem, even if the Earth is no
longer habitable. To find out its fate, Loeb and Cox tagged
all the stars in the simulation that currently share the
Sun's orbit around the Milky Way, which lies some 26,000
light years from the galaxy's centre. Then they noted the
future positions of these stars in Milkomeda.

The results suggest that the Sun will lie much deeper in
galactic suburbia than it does today, with a 67% chance of
being more than 65,000 light years from Milkomeda's centre.
However, there is also a remote 3% chance that the Sun will
jump ship and defect to the Andromeda galaxy during the
second close passage. "In the night sky, we would then see
the Milky Way from a distance," says Loeb.

Creeping sideways

The future collision has attracted growing interest over
the past decade, according to astrophysicist John Dubinski
from the University of Toronto in Canada, who has created
mesmerising animations of it online.
http://www.cita.utoronto.ca/%7Edubin...amorphosis.mov
"I'm sure this new paper will help legitimise the idea and
keep the ball rolling," he says.

But he cautions that the outcome for the Sun is far from
certain. There are various plausible models for the
structure of matter in the two galaxies that might
radically alter the Sun's final position. Another
influential factor is the transverse, or sideways, speed of
the Andromeda galaxy across the sky. Although its speed
towards us is well known, its transverse velocity has never
been measured directly.

Astronomers hope that will change after the European Space
Agency launches a spacecraft called Gaia around 2011. This
satellite will chart the positions of stars and galaxies
with unprecedented accuracy, and possibly make the first
direct measurement of the Andromeda galaxy creeping
sideways across the sky.

The research has been submitted to the Monthly Notices of
the Royal Astronomical Society.

Related Articles

Andromeda galaxy hosts a trillion stars
06 June 2006
Distance to Andromeda pinned down
12 November 2005
Distant galaxy's subtle sidling measured
03 March 2005

Web Links

Cox and Loeb abstract
T J Cox, CfA
John Dubinski, University of Toronto

More at:
http://space.newscientist.com/articl...and-earth.html

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