CNN.com - Galaxies in Hubble pic see stars after crash
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By Richard Stenger
CNN Sci-Tech Writer
(CNN) -- A galactic quintet with an angelic reputation actually harbors some fiendish galaxies, including marauders with a penchant for smacking into one another, Hubble astronomers said Thursday.
The group of galaxies became well known as the heavenly headquarters of God and his angels in the 1946 movie classic, "It's a Wonderful Life."
At least two members of the galactic gang, however, instigated hit-and-run collisions, wrenching stars and gas from their neighbors and hurling them into space.
Besides disrupting the neighborhood, some 270 million light-years away in the constellation Pegasus, the demolitions gave rise to a great proliferation of stellar life.
The intense gravity of the colliding galaxies squeezed sprawling clouds of hydrogen, igniting millions of stars in dozens of young star clusters and perhaps spurring the birth of several dwarf galaxies.
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The chaos in the compact galactic cluster known as Stephan's Quintet is particularly interesting to scientists.
"It may be a local example of phenomena typical of the early universe when encounters were much more common," said Sarah Gallagher of Pennsylvania State University, one of the Hubble researchers.
For years, scientists have studied the clusters, but could only crudely estimate their ages until the Hubble space telescope took a look.
"Hubble's superb resolution allowed us to discover and pin down the ages of these clusters," said Gallagher, who published her findings in the July 2001 issue of Astronomical Journal.
Star births have taken place in three major regions around the quintet, according to Gallagher and her colleagues. The ages range from 2 million to more than 1 billion years old, depending on the location of the clusters.
Some formed in an area in the top left of the image, known as the northern starburst region. Others came into being in the tidal wake of a collision between NGC 7318A and NGC 7318B, a galactic duo that resembles twin egg yolks in the top right of the image.
| Galactic gangs in Stephan's Quintet bring chaos and life | |
The event stretched one of the spiral arms on NGC 7318B, stoking a wave of star births. While the encounter happened about 20 million years ago, Hubble observations suggest that stars have formed as recently as 2 million years ago.
"The range of ages of these young clusters indicates that the star formation in that region may be self-propagating. The deaths of massive stars in each starburst region seed the next generation," said Hubble scientist Jane Charleton.
Another bump that stoked the star population involved a galaxy well out of the picture. NGC 7320C barreled into the quintet several hundred million years ago, pulling the tail of NGC 7319, the galaxy in the left side of the image.
The 100,000 light-year long tail boasts the richest known crop of dwarf galaxies born in gaseous debris, as many as 15, according to the Hubble scientists.
The astronomers on Thursday released the image, a mosaic composed of archive Hubble photographs.
