Featured Image: Tracking Motions of Local Galaxies


What’s with all the dots? You’re looking at the positions of thousands of stars observed by the Gaia mission in and around two nearby galaxies: Andromeda (M31) and Triangulum (M33). In a new study led by Roeland van der Marel (Space Telescope Science Institute and Johns Hopkins University), a team of scientists used stellar proper-motion observations from Gaia’s second data release, DR2, to track the 3D movement of these two galaxies. The precision of the Gaia data allowed the authors to update our best estimates about how these galaxies are interacting with each other and with the Milky Way, both now and in the future. Van der Marel and collaborators find that the Triangulum galaxy is likely on its very first infall into Andromeda, suggesting it’s not to blame for Andromeda’s previously formed tidal warps and tails. And Andromeda itself appears to be on a less direct path toward us than we’d previously thought, suggesting the collision between Andromeda and the Milky Way may be only glancing, and it won’t occur for another 4.5 billion years. For more on the authors’ conclusions, check out the article below.


“First Gaia Dynamics of the Andromeda System: DR2 Proper Motions, Orbits, and Rotation of M31 and M33,” Roeland P. van der Marel et al 2019 ApJ 872 24. doi:10.3847/1538-4357/ab001b