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collision
Mergers of Gas-Rich Disk Galaxies
Joshua E. Barnes (Institute for Astronomy, University of Hawaii)
Video: 1 MB, MPEG
What happens when two galaxies merge? The answer to this question lies in the mass of each galaxy. If one galaxy is significantly larger and more massive than the other, the smaller galaxy could become completely absorbed by the larger one. If the masses are comparable, a number of outcomes are possible. The galaxies may pass right through one another, remaining, for the most part, intact as separate gravitational entities (albeit disrupted). Often these two galaxies will collide again, either forming a new structure from the merger or becoming two dwarf galaxies that are a fraction of their original sizes.
What happens inside a merging galaxy?
Inside galaxies, stars are relatively far apart. Therefore, when galaxies collide, the likelihood of the individual stars colliding are minimal. However, what fills the space between the stars is the gas and dust of the galaxy. When these clouds of gas and dust collide with one another, a great deal of turbulence is created which disrupts the gas clouds. As the particles are forced together at high speeds, areas of extreme pressure are created. These active pockets will eventually explode into regions of renewed stellar birth.
The Simulation
This simulation demonstrates a merging of two gas-rich disk galaxies. Only the gas particles are shown. The colors indicate the energy dissipated by shocks arising from the collision (blue is lower energy). Ultimately, the galaxies merge into one body giving birth to new star-forming regions and a new galaxy.
Eve Klein
Milky Way-Andromeda Galaxy Collision
John Dubinski (University of Toronto)
Video: 1016 kB, MPEG
We live in the Milky Way Galaxy, a collection of gas, dust, and hundreds of billions of stars. About two million light years (20 billion billion kilometers) away lies the Andromeda Galaxy, a spiral galaxy similar in size and shape to our Milky Way. Current measurements suggest that, in about three billion years, the Milky Way and Andromeda galaxies may collide. What will happen? The stars in the galaxies, our Sun included, will probably not hit each other, but the galaxies' mutual gravity will probably pull, twist, and distort them until, about a billion years later, a new elliptical-shaped galaxy is born.
Gravity and tides at work
This movie shows a supercomputer simulation of one possible collision scenario between the Milky Way and Andromeda. Each spiral galaxy is represented by a disk of stars surrounded by a spherical dark matter
halo. The simulation contains over 100,000,000 virtual particles. The Milky Way is shown face-on and is initially at the bottom of the frame while Andromeda moves from the top of the frame down and is tilted from this perspective. The movie's field of view is about one million light years (10 billion billion kilometers) across, and the total elapsed time of the movie is about 1 billion years. The complex patterns and structures created during the collisions are caused by tides, the same process that works on Earth's oceans. The gravitational pull of the each galaxy's stars and dark matter twist, tear, and distort their original disk-like structures, leaving a single elliptical galaxy and lots of tidal debris after all is said and done.
The Simulation
This simulation demonstrates a merging of two gas-rich disk galaxies. Only the gas particles are shown. The colors indicate the energy dissipated by shocks arising from the collision (blue is lower energy). Ultimately, the galaxies merge into one body giving birth to new star-forming regions and a new galaxy.
Gordon Myers
Galaxies Colliding: Edge-On View
Chris Mihos (Case Western Reserve University)
Video: 1 MB, MPEG
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
