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  sci-tech > space > story pagecorner  

Hubble reveals galactic collisions more common than expected

Hubble images of colliding galaxies

November 22, 1999
Web posted at: 3:57 p.m. EST (2057 GMT)

In this story:

More collisions than expected

Evidence stacking up


GREENBELT, Maryland (CNN) -- Astronomers using the Hubble Space Telescope have found evidence of the galactic equivalent of a rush hour multi-car pileup.

Scientists at the Goddard Space Flight Center, in Greenbelt, Maryland, say they've gathered information that indicates the rare ultra-luminous infrared galaxies are involved in collisions more frequently than scientists believed, with fiery pile-ups taking place where three, four or even five galaxies smash together.

For three years, scientists studied 123 of the galaxies within 3 billion light-years of Earth. They found that over two dozen of them apparently were involved in multiple collisions.

More collisions than expected

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Before the new images from Hubble, astronomers thought only pairs of galaxies were interacting to create the infrared galaxies. But astronomer Kirk Borne used the Hubble to get a better look, sort of like using a traffic camera here on Earth to zoom in on an accident on a heavily traveled freeway.

"If you were in the backup of an accident you might see only a couple of cars when several were involved," Borne said. Hubble allowed Borne to get a better view of the galactic collision.

Ultra-luminous infrared galaxies are rare -- only about one in a million galaxies fall into this class. Borne said that may be because it takes several colliding galaxies to form them.

"We realized that it takes more than two of these galaxies colliding to make the infrared firestorm," Borne said.

Borne says he found strong visual evidence that about 30 percent of the galaxies involve multiple collisions. He and his team plan to do follow-up observations to measure the speed of the galaxies. That should tell them if they really are plowing into each other in the manner suspected by scientists.

Borne also says the results of the Hubble data offer a snapshot of what conditions were like early in the universe, when galaxy collisions were commonplace.

Evidence stacking up

Ultra-luminous infrared galaxies were first detected by the IRAS satellite in the early 1980s. They glow in infrared light, 100 to 1,000 times brighter than our Milky Way galaxy. The infrared glow is caused by a firestorm of stars being created as the galaxies collide. Large amounts of dust absorb and re-radiate the light of the hot newborn stars.

Early on, scientists noticed that the infrared galaxies were oddly shaped. Most galaxies are spiral, like our own Milky Way, or they're round. The infrared galaxies have long streamers of stars or protrusions.

Borne says scientists suspected the galaxies might be misshapen because of the force of another nearby galaxy.

Then in 1998, a team of Japanese scientists, Y. Taniguchi and Y. Shioya, theorized there might be even more than two galaxies involved.

"The Hubble results support this hypothesis," Borne says.

Borne's research has been submitted for publication in the Astrophysical Journal Letters.

The Hubble Space Telescope is a project of NASA and the European Space Agency.

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Space Telescope Science Institute
Hubble Heritage Project Dust Jacket
The Next Generation Space Telescope Home Page
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