Four stars near the bright band of the Milky Way have revealed a secret: the presence of a hidden dwarf galaxy.
Six years ago astronomers predicted that such a galaxy might be in that region based on observed ripples in the Milky Way’s disk. The galaxy is small, faint, and dominated by invisible dark matter. That combination obviously makes it very hard to see. Furthermore, it lies behind a shroud of dust that blocks any visible light from passing through.
Now scientists have identified four stars that appear to belong to the galaxy by examining infrared light, which can cut through dust. The stars are known as Cepheid variables. They pulse brighter and dimmer in a predictable pattern, which allows astronomers to determine how far they are from us—about 300,000 light years. That distance puts them well beyond the main body of the Milky Way and right where an orbiting dwarf galaxy might lie. The finding is in the Astrophysical Journal Letters. [Sukanya Chakrabarti et al, Clustered Cepheid Variables 90 kiloparsec from the Galactic Center]
Dwarf galaxies like this one are thought to contain more dark matter than regular matter. So tracking down such dwarfs could give researchers more clues in the quest to figure out what dark matter is made of.
—Clara Moskowitz
