The Milky Way is on a path of destruction. In 5 billion years, it will smash into Andromeda, the biggest spiral galaxy in the neighborhood. The collision will create legions of giant new stars, up our quotient of radiation-spewing supernovas, and feed a lot of matter into the mouths of massive, massive black holes. Beyond that, there are a whole lot of maybes and probablys.
The quest to understand exactly how the bust-up will happen is giving scientists a good excuse to rubberneck elsewhere. Using images from two NASA space telescopes—the Spitzer, which captures infrared, and the Galaxy Evolution Explorer, which picks up ultraviolet—Lauranne Lanz of the Harvard-Smithsonian Center for Astrophysics and her colleagues are cataloging cosmic train wrecks. The result of their research is more than 50 images of galaxies in different collision states. The collection helps us understand our galaxy’s future by zooming in on crashes past.
Example 1: PURSUIT
Separated by 160,000 light-years, the galaxies NGC 470 (left) and NGC 474 (right) are on the approach. Eventually, they will swing past each other, pulled in by gravity and propelled by inertia, before turning back to hit head-on. In these images, ultraviolet light appears blue, and infrared appears green (near-infrared) and red (mid-infrared).
Example 2: IMPACT
When these two systems (NGC 935 and IC 1801) smash, gases are compressed and heated, becoming dense enough that fusion starts. Then stars are born (shown here in blue). This process is a little slower than American Idol. The large star below the galaxies is much nearer than the train wreck, in our own Milky Way.
Example 3: MERGER
Finally, two become one. “These galaxies are so indistinguishable that the pair has only one name,” Lanz says of NGC 520. Tidal tails stretching from the top right to the bottom left show stars, gas, and dust ripped from the central galaxies. When the crash with Andromeda happens, our own sun may be one of those tossed out into exile.