Research Progress Based on Gaia DR2 and the Comparison of the Gaia Proper Motions to the Galaxia Model of the Milky Way

Abstract

The background of the Gaia Data Release 2 (DR2) is introduced and research progress based on Gaia DR2 is reviewed. Gaia DR2 coordinates and proper motions are transformed to Galactic coordinates to allow for a comparison of the Gaia data to models of the Galaxy. A comparison of the absolute predicted and measured numbers of stars per unit area on the sky as well as the corresponding proper motions in Galactic X, Y, and Z are made. It is found that there is a very big difference between the measurements taken from the Gaia Survey and the predictions made by the Galaxia Model of the Galaxy for the proper motions. A further in depth analysis, taking into account the proper motions as a function of distances, is required to fully understand the discovered discrepancies.