Multiple Galaxy Collisions Surprise Hubble Astronomers

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November 22, 1999: Wrecks between two galaxies were a common occurrence in the early cosmos. But pileups among several galaxies? Astronomers conducting a three-year survey of ultra-luminous infrared galaxies (ULIRGs) have discovered more than 24 of them involved in three-, four-, or even five-galaxy smashups. Astronomers have made this discovery by analyzing Hubble telescope pictures of these pileups, including the nine presented here. These results offer a snapshot of what conditions were like in the early universe, when galaxy collisions were commonplace.

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Q & A: Understanding the Discovery

1. 1. How can astronomers look at the images and tell that multiple galaxies are colliding?




These tangled-up looking snapshots resemble computer simulations of multiple galaxy collisions. In these pictures, astronomers see matter ripped out of galaxies, forming long tails of stars, and multiple nuclei crowded together. In some, researchers see a "nest" of galaxies coalescing. For conclusive proof of multiple galaxy collisions, researchers have scheduled spectroscopic observations to measure the collision speeds of the wayward galaxies. These speeds determine whether the galaxies occupy the same location and if they're moving slowly enough to merge.