Gaia DR2 Improves Encounter-Time Estimates For Local Group Galaxies

Video is Hubblecast 55: Crash of the Titans via HubbleESA and YouTube.

A new paper has been published in Astrophysical Journal – (ArXiv Preprint) giving the latest measurements for Proper Motion trajectories of the nearby galaxies, Andromeda (M31) and Triangulum (M33) – obtained by combining Gaia Data Release-2 with previous Hubble Space Telescope and VLBI data. Together with our own Galaxy, and the previously-published data for the LMC, these are the 4 most-massive galaxies in our Local Group.

So, using this data, they have been able to calculate the latest estimates for the encounter and merger time for Andromeda and our own Galaxy. As expected, the time is somewhat longer than previous estimates. Also the initial encounter will be more glancing than previously projected.

They estimate 4.5 GYr for the peri-time using just Andromeda and our own Galaxy, with an estimate of a further 1 GYr, if they include M33 and the LMC.

They note that

“A more detailed analysis, searching the full PM error space, coupled with full N-body simulations of the 4-body encounter are needed to fully describe the future dynamics and merger of the MW-M31 system.”

So it looks like we are looking at something like a realistic 5.5 GYrs for the first galactic encounter. This is obviously a little longer than the natural, unmodified fusion-lifespan of our Sun – so we will probably not be solely dependent on our own home star by then. If we are a galactic species, then our distant descendants may even be able to hop across to Andromeda as it gets close. There will be millions of years, during which the nearest outliers of Andromeda will be within fusion or laser starship range of the outlier systems of our own Galaxy. Naturally, the two galaxies will tidally-warp each other as they get within close range.

Obviously I will add any video links I find, to this blog post as I locate them.

Adventurous future readers of this blog, who plan to migrate to Andromeda, should probably make sure to book ahead. But fortunately, you still have plenty of time to prepare.