Our galaxy, the Milky Way, is surrounded by about fifty dwarf galaxies. Most of these galaxies are only identifiable through telescopes and have been named after the constellation in which they appear on the sky (for example, Draco, Sculptor or Leo). However, the two most obvious dwarf galaxies are called the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), and these are easily visible to the unaided eye. Traditionally these dwarf galaxies have been thought of as satellites in orbit around the Milky Way for many billions of years. Now, however, new data from ESA’s Gaia spacecraft have shown that the majority of the dwarf galaxies are passing the Milky Way for the first time. This forces astronomers to reconsider the history of the Milky Way and how it formed, along with the nature and composition of the dwarf galaxies themselves.
ESA/Gaia/DPAC, CC BY-SA 3.0 IGO