Ancestors of Milky Way-Type Galaxies Found, Analyzed

January 9, 2008

Scientists have peered back into the earliest epochs of the universe and discovered the types of galaxies that form modern galaxies, including spiral types like our Milky Way.

The newfound galaxies represent some of the first to form in the universe—their light has traveled between 9 and 12 billion years to reach Earth, the bulk of the universe's 13.7-billion-year existence.

The discoveries help unravel the mysterious origins of the modern universe, sort of like finding a key fossil in the path of human evolution, according to one of the researchers.

The discoveries were described to reporters Tuesday at the American Astronomical Society annual meeting in Austin, Texas.

Milky Way Ancestors

Eric Gawiser is an astrophysicist at Rutgers University in New Brunswick, New Jersey. He said researchers have now directly observed Lyman alpha galaxies, the building blocks of spiral galaxies.

These ancient galaxies are more efficient than others at star formation, producing numerous hot and bright stars that ionize the hydrogen atoms around them. This causes the galaxies to emit a telltale band of ultraviolet light called Lyman alpha.

Previously, researchers had only been able to observe the light emissions and had to extrapolate that they came from galaxies. (Related: "Faint 'Teenage' Galaxies Found in Early Universe" [November 29, 2007].)

The newfound galaxies are tiny, only about 10 percent of the size and 5 percent of the total mass of the Milky Way. They also have only about a fortieth as many stars as in present-day spiral galaxies.

The Milky Way is thought to have at least 200 billion stars.

"We're seeing a very different kind of object in the early universe," Gawiser said at the briefing.

"Several of these objects will have to merge together and additionally add mass accreted from the cosmos in order to form a single, modern-day spiral galaxy."

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