Cannibal Galaxy In Our Back Yard

The brightest galaxy visible in the night sky outside our own Milky Way is busy gobbling up its neighbours, astronomers at Cambridge have discovered.

The Andromeda Galaxy, M31, which can be seen with the naked eye as a fuzzy blob containing a trillion stars, lies only about 2.5 million light-years away – right on our cosmic doorstep.

Scientists observed wispy streams of stars on the fringes of Andromeda – the leftover remains of smaller galaxies that it has absorbed.

And they say that another spiral galaxy in our neighbourhood, M33 in the constellation of Triangulum, is destined to be a future victim.

The Cambridge astronomers were part of an international team that made a million light-year-wide survey of the Andromeda Galaxy and its surroundings using a powerful digital camera on the giant Canada-France-Hawaii telescope on Mauna Kea, Hawaii.

They discovered that some clumps of stars in Andromeda could not have formed within that galaxy because there would not have been enough gas there to be born from. They deduced therefore that they were from smaller galaxies it had digested.

Dr Mike Irwin, of Cambridge’s Institute of Astronomy, is a lead author of a report by the team in Nature. He said: “This is a startling visual demonstration of the truly vast scale of galaxies. The survey has produced an unrivalled panorama of galaxy structure which reveals that galaxies are the result of an ongoing process of accretion and interaction with their neighbours.”

Their results also suggest that Andromeda is interacting with the Triangulum Galaxy. Dr Scott Chapman, of the Institute of Astronomy, said: “Ultimately, these two galaxies may end up merging completely. Ironically, galaxy formation and galaxy destruction seem to go hand in hand.”

M31 was thought to be the largest galaxy in our so-called Local Group, but other work at Cambridge has suggested that our Milky Way is bigger. In June astronomers announced they had found the first planet in our Andromeda galaxy neighbour.

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