The aftermath of the Great Collision between our Galaxy and the Large Magellanic Cloud

TL;DR

This paper predicts an imminent collision between the Milky Way and the Large Magellanic Cloud, which will significantly alter the Milky Way's structure, black hole mass, and stellar halo, restoring its typical galactic features.

Contribution

It provides the first detailed simulation-based prediction of the Milky Way-LMC merger timeline and its transformative effects on galactic properties.

Findings

LMC will merge with the Milky Way in approximately 2.4 Gyr.

The supermassive black hole will grow up to 8 times in mass.

The stellar halo will become 5 times more massive and attain typical metallicity.

Abstract

The Milky Way (MW) offers a uniquely detailed view of galactic structure and is often regarded as a prototypical spiral galaxy. But recent observations indicate that the MW is atypical: it has an undersized supermassive black hole at its centre; it is surrounded by a very low mass, excessively metal-poor stellar halo; and it has an unusually large nearby satellite galaxy, the Large Magellanic Cloud (LMC). Here we show that the LMC is on a collision course with the MW with which it will merge in $2.4^{+1.2}_{-0.8}$ Gyrs (68% confidence level). This catastrophic and long-overdue event will restore the MW to normality. Using the EAGLE galaxy formation simulation, we show that, as a result of the merger, the central supermassive black hole will increase in mass by up to a factor of 8. The Galactic stellar halo will undergo an equally impressive transformation, becoming 5 times more massive. The additional stars will come predominantly from the disrupted LMC, but a sizeable number will be ejected onto the halo from the stellar disc. The post-merger stellar halo will have the median metallicity of the LMC, [Fe/H]=-0.5 dex, which is typical of other galaxies of similar mass to the MW. At the end of this exceptional event, the MW will become a true benchmark for spiral galaxies, at least temporarily.