Ancestors of Milky Way-Type Galaxies Found, Analyzed

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Gawiser and his colleagues ran computer simulations and statistical analyses of how galaxies cluster together to determine that only Lyman alpha galaxies could merge into spirals like the Milky Way.

Other types of early galaxies would become too large after mergers to form a typical spiral. They form so-called elliptical galaxies instead.

"This determines that the typical present-day descendant of the galaxies we've identified is indeed a typical-mass galaxy like the Milky Way, which would typically be a spiral," Gawiser said.

Massive Relics

Some of these other types of galaxies in the very early universe were anything but tiny, pointed out Elizabeth McGrath, an astrophysicist at the University of California, Santa Cruz.

She presented research on massive disk-shaped galaxies spied by the Hubble Space Telescope.

These galaxies are more massive than the Milky Way, yet they formed when the universe was only a fifth its current age. (Related: "Giant 'Blob' Is Largest Thing in Universe [July 31, 2006].)

Surprisingly, McGrath noted, several of the galaxies were flat, pancake-like disks—not the football-shaped elliptical galaxies that form when galaxies merge. Such elliptical galaxies are common in the local universe.

"These could not have been formed through galaxy mergers," she said. "More likely they were formed from the rapid collapse of a massive gas cloud."

This contrasts greatly with the commonly held belief that all massive galaxies formed by a slow, gradual coalescence of smaller galaxies, McGrath noted.

McGrath and her colleagues believe the disk-shaped galaxies eventually collide with other old galaxies and then reform into the elliptical-shaped galaxies present in the local universe.

"These massive galaxies are very different than the galaxies we see in the local universe," she noted.

In a telephone interview after the briefing, Gawiser noted that these disk-shaped galaxies are "about a hundred times more massive than the Lyman alpha emitters and much rarer" in the early universe.

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