The M31 Velocity Vector. III. Future Milky Way-M31-M33 Orbital Evolution, Merging, and Fate of the Sun

TL;DR

This study predicts the future orbital evolution and merging of the Milky Way, Andromeda, and Triangulum galaxies using simulations, indicating a likely merger in about 6 billion years and potential impacts on the Sun's position.

Contribution

It provides detailed predictions of the MW-M31-M33 system's future, incorporating observational uncertainties and exploring various merger scenarios with probabilistic outcomes.

Findings

MW and M31 will merge in approximately 5.86 Gyr.

There is a 41% chance M31 will directly hit the MW.

The Sun is likely to be farther from the galactic center after the merger.

Abstract

We study the future orbital evolution and merging of the MW-M31-M33 system, using a combination of collisionless N-body simulations and semi-analytic orbit integrations. Monte-Carlo simulations are used to explore the consequences of varying the initial phase-space and mass parameters within their observational uncertainties. The observed M31 transverse velocity implies that the MW and M31 will merge t = 5.86 (+1.61-0.72) Gyr from now, after a first pericenter at t = 3.87 (+0.42-0.32) Gyr. M31 may (probability p=41%) make a direct hit with the MW (defined here as a first-pericenter distance less than 25 kpc). Most likely, the MW and M31 will merge first, with M33 settling onto an orbit around them. Alternatively, M33 may make a direct hit with the MW first (p=9%), or M33 may get ejected from the Local Group (p=7%). The MW-M31 merger remnant will resemble an elliptical galaxy. The Sun will most likely (p=85%) end up at larger radius from the center of the MW-M31 merger remnant than its current distance from the MW center, possibly further than 50 kpc (p=10%). The Sun may (p=20%) at some time in the next 10 Gyr find itself moving through M33 (within 10 kpc), but while dynamically still bound to the MW-M31 merger remnant. The arrival and possible collision of M31 (and possibly M33) with the MW is the next major cosmic event affecting the environment of our Sun and solar system that can be predicted with some certainty. (Abridged)