When Galaxies Collide: Star Formation and the Feeding of Black Holes

Professor Susan Lamb
Physics and Astronomy, UIUC

The material in the universe is streaming apart, apparently at an accelerating rate. However, the pull of gravity is always present, countering the outward motion and slowing material so much in some regions of the Universe that it wins and objects can form. Galaxies are evidence of this process at work. They are made up of dense stars, diffuse gas, dust that formed from these, and vast amounts of dark matter that can only be detected through its gravitational pull on the material that shines, such as stars. The galaxies, once formed, are not "islands unto thenselves"; they fly past one another, sometimes at very high speeds, they collide and sometimes merge into a new object, a galaxy looking very different to the two original systems. These dynamical processes have a big effect on the gas inside the galaxies. It clumps, it is shocked, and it it thrown out of the galaxy or rammed towards the center. In the process, new stars are formed and gas can be chaneled down towards the galactic centers to feed the massive Black Holes that appear to be ubiquitous inhabitants of such regions. I will display some recent observations of colliding and merging galaxies taken with a variety of telescopes, and demonstrate how we can simulate some of the basic physical processes that take place in these systems using supercomputers and visualization of the results in movies.

Simulated and Observed Ring Galaxies, produced by collision with a second galaxy.