Milkomeda and the Fate of the Milky Way

Abstract

Few galaxies exist in isolation. Thus, despite the grand tour all take through our expanding universe, most are invariably bound by gravity to one or more others. We like to think that on the scale of the local universe, most galaxies must be far apart, and if we consider it is 2.2 million light years to M31, Andromeda, it does seem a rather long way. Yet the distance between the Milky Way and Andromeda galaxies is roughly 20 times their diameter: just imagine a universe if the distance between every star was only 20 times its diameter. Two million (plus) light years may be big on our scales—or even that of the Solar System, but it is relatively puny compared to the size of the galaxies themselves. With each galaxy bearing a mass measured in hundreds of billions (or even trillions) of solar masses, gravity can turn a seemingly solitary, sedate galaxy into a rampaging train wreck.