"It's as if we're listening to a symphony and we want to make sure we listen to all different parts of the orchestra," she said of the multiwavelength study.
"If we limit ourselves to one wavelength—if we only listen to the wind section—we don't see the full picture of our studies of galaxy evolution."
The full analysis shows that galaxies undergo violent changes as they are pulled by the attractive force of gravity through the outskirts of the clusters toward the dense cluster cores.
"As these galaxies move in from the country to the big city, it's in the suburbs where we see them in the process of change," she said.
For example, some galaxies are stretched as they quickly slide past each other. Others have their gas slowly sucked out by the gravity of another, rendering them unable to make new stars.
"There're even more violent processes, like stripping: The gas is pulled out all together as they plunge into these dense regions," Gray said.
Gray noted that the galaxies in the center of the clusters look different—they're older, deader, and less dense.
Perhaps, she said, the central galaxies move so quickly in their orbits that they are unable to attract each other and collide as they do in the suburbs.
The researcher noted that the highly detailed map of Abell 901/902 allowed them to catch the galaxies at just the right moment to see these changes. But results from other teams studying the same supercluster seem to back up the findings.
"We see more collisions between galaxies in the regions toward which the galaxies are flowing than in the centers of the clusters," Shardha Jogee of the University of Texas in Austin commented in a press release.
Jogee presented unrelated research at the AAS meeting that used images from space-based telescopes to show that galaxies in the local universe go through a "mid-life crisis" and stop merging as frequently and violently as they did when the universe was young.
By the time galaxies reach the center of their clusters, Jogee said, "they are moving too fast to collide and merge, but in the outskirts their pace is much more leisurely, and they still have time to interact."
(Victoria Jaggard in Austin, Texas, contributed to this report.)
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