NEW YORK — Galaxies quite commonly collided when the universe was about half its current age, suggesting that many galaxies were built up by such cosmic mergers, according to a new study.
Scientists peered over very long distances, which let them see galaxies as they existed billions of years ago. They found many faint galaxies that looked like they were merging, said researcher Roger Windhorst.
Some galaxies appeared to be tugging on each other with gravity. In other cases, the galaxies appeared to be so close that their mutual attraction would eventually pull them together, said Windhorst, of Arizona State University in Tempe.
Windhorst and other scientists report in the June issue of the journal Nature that they combined observations from the Hubble Space Telescope and the Very Large Array radio telescope in New Mexico. They found that most of a series of faint radio-wave sources were the merging galaxies.