November 25, 2010

Collision Of Galaxies Likely Formed Andromeda

The Andromeda Galaxy was formed as the result of a massive collision involving two separate galaxies that occurred billions of years ago, an international team of researchers has discovered.

The astronomers, led by Francois Hammer of the Paris Observatory, conducted complex computer simulations of the galaxy's structural formation, both in France and at the National Astronomical Observatory of China (NAOC). They then analyzed the results and prepared a study, which has been published in the Astrophysical Journal.

According to their findings, Andromeda, the spiral galaxy closest to the Milky Way, was formed when two galaxies--one slightly larger than the Milky Way, and the other about a third of our galaxy's size--began merging some 9 billion years ago.

The process, they say, took about 3.5 billion years to complete and would have "must have been particularly violent to generate the rotation required to form the Andromeda Galaxy's giant disk," according to John Roach of MSNBC.com. Furthermore, Roach notes that the simulations showed that mass expelled during the collision could have gone on to form the Magellanic Cloud, "which today are satellite galaxies attached to the Milky Way."

Hammer told BBC News Science Reporter Katia Moskvitch that, while scientists have been able to detect far away galaxies, the 40 galaxies closest to us--known as the Local Group--still contain many mysteries. While Hammer said that "many astronomers, especially specialists in this field, thought that the Andromeda galaxy could be the result of a major merger," the theory had yet to have been tested.

He also told Moskvitch that his team's discovery had "the potential to revise all our knowledge about the Local Group--and this may have also an impact regarding the amount of dark matter in galaxies." He also said that it could provide clues as to how our own galaxy formed--though if it was created by a collision, like Andromeda was, Hammer says it would have occurred "much earlier."

Andromeda, also known as Messier 31 or M31, is located 2.5 million light years away. It was named for a mythological Greek princess and is located in a constellation also known as Andromeda. According to a 2009 study, it is approximately the same mass as the Milky Way, though previous estimates placed it at about 80 percent of our galaxy's size. It has an apparent magnitude of 3.4, making it one of the brightest of the Messier objects and visible to the naked eye under the right conditions.


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