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Cosmic hit-and-run gives galaxy starry tail A cosmic hit-and-run between two speeding galaxies has left one with a wispy tail speckled with stars, according to a new snapshot from a NASA space observatory.
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A cosmic hit-and-run between two speeding galaxies has left one with a wispy tail speckled with stars, according to a new snapshot from a NASA space observatory.

The new galaxy tail photo reveals the aftermath of a collision between the galaxy IC 3418 and a member of its neighboring Virgo galaxy cluster.

The galactic smash-up occurred 54 million light-years from Earth and was spotted by NASA's Galaxy Evolution Explorer (GALEX) observatory. These new observations from GALEX will help give astronomers a better understanding of how stars form, researchers said.

"The gas in this galaxy is being blown back into a turbulent wake," said Janice Hester of the California Institute of Technology in Pasadena, Calif., lead author of a recent study that was published in the Astrophysical Journal Letters.

But stars still manage to form despite rough conditions in the galaxy's tail, which stems from a mix of stellar winds and interstellar gas, Hester added.

"The gas is like sand caught up by a stiff wind," she explained. "However, the particular type of gas that is needed to make stars is heavier, like pebbles, and can't be blown out of the galaxy. The new Galaxy Evolution Explorer observations are teaching us that this heavier, star-forming gas can form in the wake, possibly in swirling eddies of gas."

When galaxies collide
Galaxy collisions are not uncommon in the universe. In fact, it is estimated that our own Milky Way galaxy will eventually crash into the Andromeda galaxy in a few billion years.

Galaxies can become tangled together, kicking gas and dust into space around them. The galaxies that emerge from these tussles a little worse for wear are left with tails of material stripped off during their violent encounters.

Hester and a team of astronomers closely examined the tail of IC 3418, which actually formed in a very different way. Instead of bumping up against one galaxy, IC 3418 is mingling with the entire Virgo cluster of galaxies.

This massive galaxy cluster – which contains approximately 1,500 galaxies and is permeated by hot gas – is pulling IC3418 in, causing it to plunge through the cluster's gas at a blistering rate of over 2 million mph (3.2 million kph).

At this extraordinary speed, IC 3418's gas is being shoved back into the choppy tail that is visible in the new image.

Ultraviolet galaxies
The researchers were able to track the galactic tail of IC 3418 using GALEX, which observes the universe in ultraviolet wavelengths in order to measure the history of star formation. The tail is studded with clusters of massive, young stars that glow with ultraviolet light that is easily spotted by the GALEX space telescope.

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The tail's young stars indicate that a crucial ingredient for star formation – dense clouds of gas called molecular hydrogen – formed in the wake of IC 3418's galactic plunge.

This is the first time astronomers have found solid evidence that clouds of molecular hydrogen can form under the violent conditions present in a turbulent wake, researchers said.

"IC 3418's tail of star-formation demonstrates that strong turbulence promotes cloud formation," said Mark Seibert, a co-author of the paper and a member of the Galaxy Evolution Explorer science team at the Carnegie Observatories in Pasadena.

Galaxy tails provide an ideal environment for isolating the factors that control star formation, said Hester.

"These tails are unique, exotic locations where we can probe the precise mechanisms behind star formation," she said. "Understanding star formation is pivotal to understanding the lifecycles of galaxies and the dramatic transformations that some galaxies undergo. We can also study how the process affects the development of planets like our own."

The Galaxy Evolution Explorer mission aims to better understand the formation of galaxies. Since its launch in 2003, GALEX has imaged over a half-billion objects across two-thirds of the sky.