What to Expect when Our Galaxy Collides With Andromeda

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]

What to Expect when Our Galaxy Collides With Andromeda

Three-color image of NGC 935 and its companion IC 1801 showing far-UV emission from young stars observed by GALEX in blue, heated dust mid-infrared emission observed by Spitzer in red, and stellar near-infrared emission observed by Spitzer in green. This pair of spiral galaxies is beginning to crash into each other.
Credit: NASA / JPL-Caltech / L. Lanz (Harvard-Smithsonian CfA)

What to Expect when Our Galaxy Collides With Andromeda

Three-color image of NGC 3448 (left) and its companion UGC 6016 (right) showing far-UV emission from young stars observed by GALEX in blue, heated dust mid-infrared emission observed by Spitzer in red, and stellar near-infrared emission observed by Spitzer in green. This pair of galaxies is only separated by 75,000 light-years, and its UV emission shows a bridge of material between the two galaxies.
Credit: NASA / JPL-Caltech / L. Lanz (Harvard-Smithsonian CfA)

What to Expect when Our Galaxy Collides With Andromeda

Three-color image of NGC 470 (top) and NGC 474 (bottom) showing far-UV emission from young stars observed by GALEX in blue, heated dust mid-infrared emission observed by Spitzer in red, and stellar near-infrared emission observed by Spitzer in green. These galaxies are likely to be on their first pass past each other and are therefore relatively undisturbed at a separation of 160,000 light-years.
Credit: NASA / JPL-Caltech / L. Lanz (Harvard-Smithsonian CfA)

What to Expect when Our Galaxy Collides With Andromeda

This montage shows three examples of colliding galaxies from a new photo atlas of galactic "train wrecks." 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 they observe different components of a galaxy. The panel at far left shows NGC 470 (top) and NGC 474 (bottom); at top right are NGC 3448 and UGC 6016; at bottom right are NGC 935 and IC 1801. In this representative-color image, far ultraviolet light from GALEX is blue, 3.6-micron light from Spitzer is cyan, 4.5-micron light from Spitzer is green, and red shows light at 5.8 and 8 microns from Spitzer.
Credit: NASA / JPL-Caltech / L. Lanz (Harvard-Smithsonian CfA)