Cosmic Catastrophes: NASA Maps Past and Future Galaxy Collisions

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In five billion years the Milky Way galaxy will collide with the Andromeda galaxy. The two galaxies will lose their separate identities as they merge into one. At the same time, the building blocks of life in the Universe — clouds of gas and dust — will collide together, triggering the birth of new stars.

Astronomers are building an atlas of galactic 'train wrecks' from past and the future — "A first step in reading the story of how galaxies form, grow, and evolve," said lead author Lauranne Lanz of the Harvard-Smithsonian Center for Astrophysics (CfA).

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."

If all goes as planned in five billion years, we'll need a new revised, Hitchhiker's Guide to Galaxy, when Andromeda may be destined to collide with the Milky Way.

Andromeda, a spiral galaxy approximately 2.5 million light-years away in the constellation Andromeda is the nearest spiral galaxy to our own, the Milky Way. Andromeda and the Milky Way are approaching one another at a speed of 100 to 140 kilometers per second (62–87 miles/sec). However, this does not mean it will definitely collide with the Milky Way, since the galaxy's tangential velocity is unknown. If they do collide, the two galaxies will likely merge to form a monster elliptical galaxy.

Andromeda, home to the evil Kelvans in an early Star Trek episode, was believed to be the largest galaxy of the Local Group of galaxies, which consists of the Andromeda Galaxy, the Milky Way Galaxy, and the Triangulum Galaxy, and about 30 other smaller galaxies. But scientists now believe that the Milky Way contains more dark matter and may be the most massive in the grouping.

However, recent observations by the Spitzer Space Telescope revealed that Andromeda contains one trillion stars, greatly exceeding the four billion stars in our own galaxy.

The Daily Galaxy via Harvard-Smithsonian Center for Astrophysics

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