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Galaxies caught in cosmic taffy pull

European Southern Observatory

(Read caption) Galactic oddball ARP 261 as seen through the European Southern Observatory's Very Large Telescope at the Paranal Observatory in Chile's Atacama Desert.

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The universe is filled with some odd-ball galaxies. Take ARP 261, for instance.

It's very a rare breed of interacting galaxies -- a so-called "taffy" pair. Only three taffy pairs have been discovered so far.

These form as two spiral galaxies smash together face-on like colliding dinner plates -- but live to tell the tale (as colliding galaxies are wont to do if one doesn't capture the other). Each galaxy passes through the other. As they separate, they exert a gravitational tug on the gas and dust in the gap between them, a bit like folks working the candy at an old-fashioned taffy pull.

For astronomer Beverly Smith, ARP 261 and its ilk represent extreme labs for studying star formation rates in galaxies that interact with one another. This week, she and her colleagues are using the Spitzer Space Telescope to observe ARP 261 and another so-called "taffy" pair of galaxies, UGC813/816.

It's all in the name of understanding what happens to rates of star formation across a range of galaxy interactions -- from the head-on collision to the near-miss.

Why bother? Early on, the universe was much smaller, and galaxy collisions -- including these cosmic high fives -- are thought to have been common. So in a sense, interacting galaxies in our own neck of the cosmos are windows on an important trigger for star formation when the universe was young.

ARP 261 is some 70 million light years away in the constellation Libra. It appears in an atlas of bizarre galaxies compiled by astronomer Halton Arp, who spent 28 years at Mt. Wilson and Mt. Palomar observatories in southern California building the cosmic photo album. It was published in 1966.


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