For that reason, the dance of the satellites tells us about the structure of the Milky Way, along with the shared history and evolution of all the galaxies involved. The result: new estimate on the mass of the Milky Way, and a fully three-dimensional map of nearly 90 objects in orbit around our galaxy. According to the standard theory of galaxy formation, small galaxies formed first, then merged to make bigger and bigger galaxies, including the Milky Way. Understanding the structure and motion of these galaxies, in other words, helps us trace the history of the Milky Way. In addition, the Gaia results show how the Milky Way is pulling some of the satellite galaxies apart, and to a lesser extent how those galaxies tug back on the Milky Way.

Source: Forbes May 02, 2018 20:48 UTC