Colliding Galaxies (4) ...

The following image shows a grazing encounter between two spiral galaxies about 35 Mpc away in the constellation Canis Major. Click on the "Show Labels" button to annotate the image.

The streamers in the lower right are about 100,000 light years long and suggest tidal disruption of the smaller galaxy on the right (IC 2163) by the larger one on the left (NGC 2207). Computer simulations indicate that IC 2163 made its closest approach to NGC 2207 about 40 million years ago and is now swinging past and behind it in a counter clockwise direction. IC 2163 does not have enough energy to escape, so it will eventually be pulled back for another encounter. The two galaxies will continue to interact and to distort each other, probably triggering massive bursts of star formation that will consume the gas and dust evident in the spiral arms. Finally, within a few billion years they will have merged into a single large galaxy.

Results from Recent Observations
As we look deeper into the Universe and therefore back in time, galaxies appear to emit more light in the blue part of the spectrum. This indicates that massive, luminous stars are forming. Since we see these distant galaxies as they were 5 to 10 billion years ago, we are witnessing events that occurred within a few billion years after these galaxies were formed.

The images of these distant blue galaxies are often distorted or contain multiple nuclei. The Milky Way seen at a similar great distance would look like a uniform disk with a single bright nucleus. Nearby "multiple-nuclei" galaxies that have been studied show the cores of individual galaxies colliding and merging into a single system of stars and gas. These collisions are violent, and take millions of years to play out, but they can trigger massive waves of star formation and indicate that the evolution of galaxies through collisions was very important in the early Universe.