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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 Jai Maharaj http://tinyurl.com/yhjyp5 http://www.mantra.com/jai http://www.mantra.com/jyotish Om Shanti Hindu Holocaust Museum http://www.mantra.com/holocaust Hindu life, principles, spirituality and philosophy http://www.hindu.org http://www.hindunet.org The truth about Islam and Muslims http://www.flex.com/~jai/satyamevajayate o Not for commercial use. 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