Galactic Collisions Leave Cosmic Skid Marks

PASADENA, CALIF. ? Cosmic debris stripped away from the wreck of colliding galaxies has been found by the Subaru telescope atop Mauna Kea, Hawaii.

The debris fields could shed light on galaxy formation and starburst activity in the early universe by allowing astronomers to retrace the paths of the colliding galaxies before they merged.

"This is equivalent to finally being able to trace the skid marks on the road when investigating a car wreck," said team member Nick Scoville of the California Institute of Technology.

Enormous debris fields found

Astronomers found the debris features in deep exposures of well-known colliding galaxies, including "the Antennae" galaxies,?65 million light-years away in the constellation Corvus, Arp 220 in the constellation Serpens (250 million light-years away), Mrk 231 in the Big Dipper (590 million light-years away), and 10 other objects. (A light year is the distance that light travels in a year, about 6 trillion miles or 10 trillion kilometers.)

The extent of the debris, some of which stretched over an area a few times larger than the Milky Way, hadn't been seen in earlier images of these collisions, astronomers said. A large extension of the Antennae was found to be twice the size previously thought, and a new tidal tail was found trailing from Mrk 231.

"We did not expect such enormous debris fields around these famous objects," said team member Jin Koda of Stony Brook University in New York.

The discoveries were announced here today at the 214th meeting of the American Astronomical Society.

Tidal tails

Colliding galaxies eventually merge and become a single galaxy. Our own Milky Way is fated to collide and merge with the neighboring Andromeda galaxy in about 5 billion years.

The mutual tug the galaxies exert on each other can pull pieces of each galaxy out in different shapes.

One example is so-called "tidal tails," which indicate a quick galactic merger. When galaxies come together quickly, they could trigger starburst activity in Ultra Luminous Infrared Galaxies (ULIRGs).

"Arp 220 is the most famous ULIRG," said team member Yoshiaki Taniguchi of Ehime University in Japan. "ULIRGs are very likely the dominant mode of cosmic star formation in the early Universe, and Arp 220 is the key object to understand starburst activities in ULIRGs."

• Video ? Galaxy Collisions
• Video ? The Biggest Cosmic Collisions
• Hubble Photos: When Galaxies Collide