July 10, 2009—A blue ridge of glowing gas seems to cut through the heart of the galaxy group known as Stephan's Quintet in a newly released picture from NASA's Chandra X-ray Observatory.
Discovered in 1877, Stephan's Quintet is really a quartet: Only four of the galaxies (above in a visual-light image by the Canada-France-Hawaii Telescope) lie close together about 280 million light-years away.
Astronomers now know that the large spiral galaxy seen at bottom left is actually a foreground object a mere 35 million light-years from Earth.
The blue ridge, revealed by Chandra's x-ray vision, is likely the result of a shockwave created as one galaxy—the centermost object in the above picture—plows past the other three at nearly 2 million miles (3.2 million kilometers) an hour.
Further studies of this group, including more detailed images like the new Chandra picture, can provide astronomers with a better understanding of galaxy evolution.
That's because galactic smashups result in alterations such as explosions of star birth, galaxy growth via mergers, and changes in shape. (Related: "Earth Likely to Relocate in Galactic Collision.")
Gravity's pull in the colliding quartet, for example, is stripping the galaxies of their cool star-forming gases, so that astronomers think in a few billion years the group's spiral-armed galaxies will become ellipses.