What Happens When Galaxies Collide?

        Our galaxy, the Milky Way, will one day collide with another galaxy. In our case, it will be the Andromeda Galaxy located 2 million light years away. The Andromeda Galaxy is moving towards the Milky Way at a speed of roughly 500,000 km per hour. The Milky Way and Andromeda Galaxies are both spiral galaxies with Andromeda being about twice the size of the Milky Way. Theories suggest that this event will take place in about 3 billion years and will not complete its galactic transformation for another 1 billion years. During these 1 billion years the gravitational forces of each galaxy will twist, pull, and distort each other to eventually form an elliptical galaxy.

        The possibility of the Andromeda-Milky Way Collision is still a theory and GalaxyDynamics.org suggests what may happen to our Solar System in the event of a collision:

        “When will this collision occur? Plausible orbits and models of the Milky Way and Andromeda galaxies suggest that the big event could occur in as soon as 3 billion years. The Sun will still be burning brightly when this collision occurs and maybe life of some sort will still be around on Earth (or at least within the solar system) at that time. So what would people see in the night sky during this billion year galactic dance? As Andromeda approaches, it will grow in size and just before the collision the night sky will be filled by a giant spiral galaxy. When the two galaxies intersect, our familiar Milky Way arch over the sky will be joined by a second intersecting arch of stars but this will only last for 100 million years or so and will be a very confusing state of affairs for galactic astronomers. Finally, when the two galaxies merge our view will depend on which direction the Sun is thrown. There are two possible fates fort the Sun which depend closely on the details of where it is in its galactic orbit at the time of the collision. In the first case the Sun may take a ride on a tidal tail and be ejected into the darkness of intergalactic space. In this case, our star would be all alone with few stellar neighbours so the night sky would be very dark with few stars to see -- maybe like the disappointing view of the nightsky from an urban centre like downtown Toronto. In the second case, the Sun may be thrown right into the centre of the merging pair where a great starburst will be underway. The huge number of stars forming will result in supernovae going off at a rate of a few per year in the new merged galaxy. While these will likely not present a direct hazard to the Earth, they will truly light up the sky letting you read at night but probably frustrating the endeavours of backyard astronomers!” (http://www.galaxydynamics.org/tflops.html)

http://www.haydenplanetarium.org/resources/ava/galaxies/G0601andmilwy

http://www.galaxydynamics.org/tflops.html

http://www.nasa.gov/audience/forstudents/5-8/features/F_When_Gallaxies_Collide.html

http://www.sciam.com/article.cfm?id=when-milky-way-and-andromeda-collide-earth-could-find-itself-far-from-home

The Colliding Spiral Galaxies of Arp 271    
Credit & Copyright: Gemini Observatory, GMOS-South, NSF