Four new satellite galaxies of the Milky Way have been discovered, bringing the total known to about 20. The pace of new discoveries suggests that many more such satellites remain unknown, which would present a serious challenge to models of dark matter as "warm", fast-moving particles.
The satellites are dwarf galaxies a few hundred to a few thousand light years across. The tiny galaxies are thought to be the building blocks of large galaxies, such as our own Milky Way – which is about 100,000 light years wide.
The four new discoveries were made by a team led by Vasily Belokurov of the University of Cambridge, UK. Named after the constellations in which they were found – Coma Berenices, Canes Venatici II, Hercules, and Leo IV, all of them lie between roughly 100,000 and 500,000 light years from Earth.
The largest and smallest are Hercules and Coma Berenices, which are about 1000 and 200 light years across, respectively. Like most of the other dwarfs discovered by SDSS, the new finds are much smaller and fainter than the 10 dwarfs that were known previously.