Draco and Ursa Minor dwarf galaxies

Two dwarf galaxies, Draco (left) and Ursa Minor (right), as viewed by ESA’s Gaia satellite using information from the mission’s second data release. 

Both are satellite galaxies of the Milky Way, held in orbit by our Galaxy’s gravity. There are a few dozen dwarf galaxies in orbit around the Milky Way. Each contains between 100 million to a few billion stars.

Using data from Gaia’s second release, astronomers have measured the motion of 12 satellite galaxies of our Milky Way. Surprisingly, the Draco and Ursa Minor galaxies seem to be moving on similar orbits, traveling together through space. 

The view is not a photograph but was compiled by mapping the total density of stars detected by Gaia in each pixel.

Acknowledgement: Gaia Data Processing and Analysis Consortium (DPAC); A. Moitinho / A. F. Silva / M. Barros / C. Barata, University of Lisbon, Portugal; H. Savietto, Fork Research, Portugal; A. Helmi, Kapteyn Astronomical Institute, University of Groningen, The Netherlands;F. van Leeuwen, University of Cambridge, UK; P. Mc Millan, Lund Observatory, Sweden