Most of the small satellite galaxies around the Milky Way's near-twin, Andromeda, are lined up in a single plane that slices through Andromeda's spiral disc, a new study reveals.
The alignment suggests the satellites are either floating on a river of dark matter or are the remains of a larger galaxy Andromeda has already cannibalised.
Astronomers have known for about 25 years that the Milky Way's dozen or so satellites line up along two planes that lie perpendicular to its disc. But how the structures formed is still not clear.
So a team led by Eva Grebel of the University of Basel in Binningen, Switzerland, set out to discover whether similar planes exist around Andromeda. At a distance of 2.7 million light years, Andromeda is the nearest large, spiral galaxy similar to the Milky Way.
The researchers plotted the positions of Andromeda's 14 satellites using images from the Hubble Space Telescope and found that nine of them lay in a relatively thin plane about 52,000 light years wide.
"It's unlikely such a plane would arise by chance," Grebel says. The satellites in the plane also shared similar characteristics – most were faint, low in mass, and had already stopped forming stars.
http://www.newscientistspace.com/article.ns?id=dn8571
