The aftermath of the Great Collision between our Galaxy and the Large Magellanic Cloud. Issue 2 (13th November 2018)

• Record Type: Journal Article
• Authors: Cautun, Marius; Deason, Alis J; Frenk, Carlos S; McAlpine, Stuart
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 483:Issue 2(2019)
• Page Start: 2185
• Page End: 2196
• Publication Date: 2018-11-13
• Subjects: Galaxy: halo -- galaxies: dwarfs -- galaxies: haloes -- galaxies: kinematics and dynamics -- Magellanic Clouds; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty3084
• Languages: English
• ISSNs: 0035-8711

Abstract

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 $2.4^{+1.2}_{-0.8}\, \rm {Gyr}$ (68 per cent 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 on to 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.