We only have five billion years left until the Milky Way galaxy crashes into Andromeda, our nearest neighbor. What will happen to us then? Because galactic collisions take place over millions or billions of years, the process isn't well understood.

That's why scientists at the Harvard-Smithsonian Center for Astrophysics have come up with an "Atlas of Galactic Collisions," a guide to the process from beginning to end. Using data from the Spitzer Space Telescope and the Galaxy Evolution Explorer (GALEX) spacecraft, Lauranne Lanz and her colleagues have created a more complete mapping of what happens when two galaxies collide. Lanz presented her findings at the meeting of the American Astronomical Society in Boston.

In the top left image from Spitzer, you can see infrared emissions from the hot dust in the galaxy M51, whereas in the right image from GALEX, you can see ultraviolet emissions from newly formed stars.

According to the press release:

The new images combine observations from NASA's Spitzer Space Telescope, which observes infrared light, and NASA's Galaxy Evolution Explorer (GALEX) spacecraft, which observes ultraviolet light. By analyzing information from different parts of the light spectrum, scientists can learn much more than from a single wavelength alone, because different components of a galaxy are highlighted.

GALEX's ultraviolet data captures the emission from hot young stars. Spitzer sees the infrared emission from warm dust heated by those stars, as well as from stellar surfaces. Therefore, GALEX's ultraviolet data and Spitzer's infrared data highlight areas where stars are forming most rapidly, and together permit a more complete census of the new stars.

In general, galaxy collisions spark star formation. However, some interacting galaxies produce fewer new stars than others. Lanz and her colleagues want to figure out what differences in physical processes cause these varying outcomes. Their findings will also help guide computer simulations of galaxy collisions.

"We're working with the theorists to give our understanding a reality check," said Lanz. "Our understanding will really be tested in five billion years, when the Milky Way experiences its own collision."

[Center for Astrophysics via Digital Journal and BBC]