Andromeda, the large, spiral galaxy visible to the naked eye as a smudge in the sky, is actually a stellar predator – eating up its neighbouring dwarf galaxies.

The evidence of "galactic dismemberment" is a stream of stars on the outskirts of Andromeda that appear to have been stripped from neighbouring dwarf galaxies.

The finding supports the theory that big galaxies grow by colliding and swallowing up smaller galaxies. It's thought that the process continues today.

Astronomers in England, France, Australia and the Netherlands made the discovery using the 2.5-metre Isaac Newton Telescope on La Palma in the Canary Islands.

The researchers say it's the first sensitive panoramic survey of Andromeda.

Andromeda is twice as large as our Milky Way galaxy and is considered its "big sister". Andromeda lies about 2.2 million light years away. It's the nearest large galaxy to our own, and can be seen in the constellation Andromeda.

The big picture

The new findings were possible thanks to digital devices that are now sophisticated enough to cover fairly large areas of sky.

Still, more than fifty long exposures had to be pieced together to take the panoramic snapshot of Andromeda.

It's predicted our galaxy will collide with Andromeda three billion years from now.

"Colliding with a dwarf galaxy is only like having a cream pie hit your windscreen," said Dr. Geraint Lewis of the Anglo-Australian Observatory in Australia.

"When our Galaxy and Andromeda collide it'll look like a car crash – very messy."

Tell-tale signs of digestion

Astronomers knew our own galaxy was a cannibal, with a tell-tale stream of stars from small galaxies it's engulfed.

Like a meal devoured by a snake, stars of a swallowed galaxy appear as a recognizable lump for billions of years before eventually mixing with the larger predator galaxy.

The ripped-off stars in Andromeda are seen as a distinct stream and can be distinguished from the larger galaxy by their slightly different chemical composition.

The study appears in the July 5 issue of the journal, Nature.