More Often Than Not, Massive Galaxies Form by Mergers

More Often Than Not, Massive Galaxies Form by Mergers
http://www.sciam.com/article.cfm?cha...1C83414B7F0000

New data seem to show that galaxies collide all the time. In fact, the
oldest and largest galaxies in the universe most likely formed from
such intergalactic combinations.

Astronomer Pieter van Dokkum of Yale University used some of the
longest and deepest sky surveys ever conducted to try to determine
whether the oldest, largest galaxies--called ellipticals because they
lack the swirling arms of the spiral type, like our own Milky
Way--formed from the collapse of ancient clouds of gas or the accretion
of smaller galaxies bumping into each other. Of the 126 galaxies of all
varieties van Dokkum looked at, 67 showed telltale signs of impact,
such as trailing tails of stars, or a collision in progress. And of the
86 oldest galaxies in the survey, 61 showed some trace of a cosmic
crash.

See: http://www.sciam.com/article.cfm?cha...1C83414B7F0000