Boundary of neighboring galaxy shifts further
The spiral galaxy closest to us, the Andromeda Nebula M 31, could be up to five times larger than previously thought, reports an international team of astronomers. The researchers had studied the movements of a group of distant stars and found that even these distant objects are still controlled by M 31's gravity.
Stars in this region had previously been counted as part of the galaxy's so-called halo – a surrounding system of old stars, globular clusters and dark matter. However, the movements of the red giant stars now observed with the Keck II telescope on Hawaii, among others, run around the center of M 31 and are therefore a real part of this galaxy, as the observations have shown.
This means that our neighboring galaxy, which is two million light-years away, extends from the center up to 500,000 light-years outwards instead of a good 100,000 light-years as previously assumed. The boundaries of the Milky Way and the Andromeda Nebula almost overlapped, according to Michael Rich of the University of California at Los Angeles. The expansion of this galaxy is "really amazing". Other groups of researchers who had previously measured M 31 would have misinterpreted stars in the outer fringes, which were still part of the actual galaxy, as already belonging to the halo.