A colliding galaxy known as the Tadpole wiggles across space in this Hubble Space Telescope image. The galaxy was either hit or sideswiped by a smaller galaxy, disrupting the larger galaxy's disk and pulling out a "tail" of stars, gas, and dust that spans a quarter-million light-years. [NASA/H. Ford (JHU)/G. Illingworth (USCS/LO)/M. Clampin (STScI)/G. Hartig (STScI)/ACS Science Team/ESA]
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A dragon and a tadpole slither low across the northern sky this evening, curling around the North Star. The dragon is the long but faint constellation Draco. And the tadpole is the aftermath of a galactic collision that’s just below the dragon’s long, winding body.
The Tadpole galaxy is about 400 million light-years away. An image from Hubble Space Telescope shows a bright “head” with a long, wiggly “tail” extending away from it.
The head is the body of the galaxy itself — a spiral that’s perhaps a little bigger than our home galaxy, the Milky Way. The tail is a streamer of stars and gas that stretches across a quarter-of-a-million light-years. It was pulled out of the galaxy’s disk by a collision with a smaller galaxy at least a hundred million years ago.
That collision squeezed vast clouds of gas in the disk and in the tail, causing them to collapse and give birth to new stars. Astronomers have discovered dozens of young star clusters, including a few that have hundreds of thousands of stars. The biggest is in the tail, and contains more than a million stars.
Eventually, the smaller galaxy will come back around and merge with the Tadpole. And much of the material in the tail will fall back onto the Tadpole, triggering the birth of even more stars. But some of the star clusters in the tail may escape, forming tiny new galaxies — the offspring of a galactic tadpole.
We’ll talk about a different kind of tadpole galaxy tomorrow.
Script by Damond Benningfield, Copyright 2014
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