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)
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
More collisions than expected
| MESSAGE BOARD|
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
"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
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
"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
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
"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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