Star-­‐Cross’d: Coming together in an expanding universe

Abstract

This is a journalistic treatment, written in the style of an article in Scientific American or a similar magazine, of the eventual merger between the Milky Way and Andromeda—an example of two galaxies coming together while the rest of the universe barrels away. We begin with a brief outline of the two galaxies—their formation, evolution, structure, and composition. We then trace the history of observations of Andromeda over the past century, with special focus on the early measurements by Vesto Slipher and Edwin Hubble and recent work by Roeland van der Marel and his colleagues on Andromeda’s proper motion. Next, we will discuss van der Marel et al.’s simulation of the collision, as well as other theoretical and observational evidence to give a more detailed account of what such a merger might look like. Finally, we examine the future of Earth, and reflect on this moment in our galactic and planetary history.