The faintest satellite galaxy yet found around the Milky Way’s near-twin, Andromeda, has been turned up by the Sloan Digital Sky Survey. The discovery suggests other dim galaxies remain undetected and goes some way towards solving a mystery known as the “missing satellite” problem. Standard theories of dark matter and the evolution of galaxies calculate that small galaxies should merge over time to form large ones, and that many of these undersized, unmerged galaxies should be visible today. The trouble is that theories predict about 100 times more dwarf galaxies than are actually observed – a discrepancy known as the missing satellite problem.
Andromeda’s New Satellite Galaxy Is Faintest Yet