Chris Mihos (Case Western Reserve University)

Galaxies like the Milky Way often have a number of much smaller, satellite galaxies orbiting around them like moths around a campfire. What happens if one of these satellite galaxies comes too close to its giant neighbor? This movie shows one possible outcome; the satellite falls to the center of the large galaxy, puffing it up in the process.

Galactic acquisition

In this simulation, we begin by looking at the two galaxies from the side. The blue ball on the right is a spherical satellite galaxy; the yellow object is a large spiral galaxy as seen from its side, or edge-on. Over the course of several hundred million years, the satellite goes above, then below the large galaxy's disk, then above again. Finally, the hapless satellite is pulled into the galactic bulge, becoming part of the now-larger galaxy.

Tracing a galactic collision

According to this supercomputer simulation, the collision tosses parts of both galaxies into a scattered halo around the disk and bulge. This result suggests that astronomers can look for such galactic crumbs to see if one galaxy has recently consumed another. The latest theories of galaxy formation suggest that our own Milky Way Galaxy may have gobbled dozens, even hundreds, of small galaxies to attain the size and mass it has today.

Charles Liu