The M31 Velocity Vector. III. Future Milky Way-M31-M33 Orbital Evolution, Merging, and Fate of the Sun
Roeland P. van der Marel (1), Gurtina Besla (2), T. J. Cox (3), Sangmo, Tony Sohn (1), Jay Anderson (1) ((1) STScI, (2) Columbia U, (3) Carnegie, Observatories)

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…
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