Tales of: History of colliding galaxies

Tales of ... A history of colliding galaxies: From oddballs to galaxy building blocks See image below

For decades, many astronomers believed in a cookie cutter universe. Orderly, well-behaved, predictable. The mold for galaxies, the large systems where stars and planets reside, came in two shapes: spirals and ellipticals. They were "island universes" that evolved in "splendid isolation" just a few million years after the Big Bang. To these astronomers, colliding galaxies were merely an oddity, an anomaly.

But there was a group of astronomers who had a less kind view of the universe. They believed that the universe was a violent place, full of collisions, cannibalism, and mergers. Galaxies, they proposed, may not have been created in cookie-cutter fashion early in the universe. Maybe collisions between spirals spawned ellipticals.

Primitive computer models

The debate over the role colliding galaxies play in galaxy evolution has continued for decades. In the 1940's, just a few years after American astronomer Edwin Hubble defined galaxy shapes, Swedish astronomer Erik Holmberg wondered what would happen if a couple of galaxies encountered one another. So he constructed an analog computer using about 200 light bulbs to simulate galaxy encounters. Based on this seemingly primitive computer simulation, Holmberg concluded that some galaxies may indeed collide, inducing tides or distortions that rob them of energy, thus causing them to slow down and eventually merge into a single galaxy. The Swedish astronomer's computer simulations also foreshadowed the important role that computers would play in studying galaxy interactions. (Continued >>)

Two gravitationally interacting galaxies, known as Arp 147, appear to form the number 10 by virtue of their orientations.

Tales of: History of colliding galaxies