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Wednesday, 4 July, 2001, 18:38 GMT 19:38 UK
Galactic cannibalism in action
Andromeda: One of the closest and largest galaxies to ours
By BBC News Online science editor Dr David Whitehouse

Astronomers have found evidence that a nearby galaxy has been devouring its close neighbours.

Deep field observations of the Andromeda galaxy show that its outer regions contain a stream of stars torn away from one of its small companion galaxies.

Observatoire de Strasbourg
The "smear" of stars across Andromeda
It adds to growing evidence from our own Milky Way that many galaxies grow and evolve by absorbing their minor brethren.

Such a detailed view is only possible for the nearest galaxies, but scientists expect that when techniques improve they will detect more examples of galactic cannibalism.

These observations are the most detailed ever made of the outskirts of one of the closest galaxies to ours.

The mighty Andromeda galaxy, similar to our own Milky Way galaxy but larger, is 2 million light-years distant (19 million million million kilometres or 12 million million million miles).

Streak of stars

A series of observations were made of it in September 2000 by the 2.5-metre (8.2 ft) Isaac Newton Telescope in the Canary Islands.

Delving deeper into its outer regions than optical observations had done before, the researchers, from Germany, Britain and Australia, found a faint streak of stars that looked as though they had been drawn from one of Andromeda's companion galaxies, called M32.

The trail of stars appears to lead directly back to M32. The astronomers say it is a true alignment, not just an apparent one, which suggests that Andromeda's gravity has disrupted the much smaller M32, tugging stars from it.

It is known that spiral galaxies, like our own Milky Way galaxy and Andromeda, are surrounded by a halo of unknown composition. This work is leading to suggestions that part of those haloes are composed of the wreckage of disrupted smaller galaxies.

The research is published in the journal Nature.

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19 May 00 | Sci/Tech
Voyage through the Universe
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Journey to the galactic core
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