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A dwarf galaxy, trailing fireballs, in its final death throes

The dying dwarf galaxy you see above, with a stream of fireballs trailing in its wake, is not big, but it is bright, and it is relatively nearby. 

It's name is IC 3418 and you'll find it deep in the Virgo Cluster -- a mass of about 1,000 galaxies not far from the smaller cluster of galaxies that includes our own Milky Way. 

Galaxy IC 3418 is dying because most of its gas has blown away and galaxies need gas to keep forming stars. In the language of astronomy, a galaxy that is no longer forming stars is a galaxy that is dead. It's kind of like the language of business: If you don't grow, you die.

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Even when the galaxy does run completely out of gas, its stars will remain and will continue to generate energy, but there will be no spiraling arms or other interesting structures that we expect to see in active galaxies.

"Once it stops forming new stars it looks much more boring, like a smooth pile of stars," said Jeffrey Kenney of Yale University, who presented research on the dying galaxy at the American Astronomical Society meeting in Indianapolis this week.

Kenney's research provides evidence that the galaxy lost its gas due to ram pressure, a powerful wind that is generated as galaxies move around in the cluster of other galaxies. The wind can get strong enough to push clouds of gas out of the galaxy, but it leaves the more dense stars behind.

"A good analogy is if you imagine holding popcorn and unpopped corn kernels in your hand and then stick your hand out a moving car window," said Kenney. "The wind would blow the popped kernels out of your hand, but leave the unpopped kernels. The popcorn are like the gas clouds, and the unpopped kernels are like the stars."

The gas is stripped away at the edge of the galaxy first, where the gravitational pull is the weakest, and continues to the core, said Kinney. This galaxy has been without its life-giving gas for some time, he said. The core has not made new stars for about 300 million years.

But while the galaxy is not making new stars, Kenney's research shows that the blobs of material trailing the galaxy are making new stars. These are fireballs, with masses of gas at the head forming bright new stars and leaving a long stream of young stars in their wake. The fireballs were formed when the gas from the galaxy was pushed out due to the ram pressure, accelerated, and then started forming stars.

Star formation can take about a million years, so we won't get to see what happens to these stars after they form. Kenney said some of the stars will fall back into the galaxy becasue they don't have enough speed to escape it, while others will just be stars in space -- the final relics of a galaxy that has lost its star-making gas.

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[For the Record, 11:38 a.m. PDT, June 5: In an earlier version of this online article,  Jeffrey Kenney's name was misspelled in a few cases.] 

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