A study of small galaxies circling around the Milky Way found that while they range dramatically in brightness, they all surprisingly pack about the same mass. The work suggests there is a minimum size for galaxies, and it could shed light on mysterious dark matter. Spinning around the Milky Way are at least 23 pint-sized galaxies, each shining with the light of anywhere from a thousand to a billion suns. Though each of these galaxies is very dim compared to large galaxies like our own, they span a large range in brightness. Astronomers led by Louis Strigari of the University of California-Irvine studied the movements of individual stars in these satellite galaxies to determine the mass of each galaxy.
By analysing light from small, faint galaxies that orbit the Milky Way, UC Irvine scientists believe they have discovered the minimum mass for galaxies in the universe 10 million times the mass of the sun. This mass could be the smallest known "building block" of the mysterious, invisible substance called dark matter. Stars that form within these building blocks clump together and turn into galaxies.