for National Geographic News
The earliest known galaxies in the universe, which formed during the universe's "dark age" nearly 13 billion years ago, have been spied by two teams of astronomers.
The discoveries, reported separately in this week's issue of the journal Nature, suggest that galaxies were forming just 700 million years after the birth of the universe.
Theory holds that the universe formed 13.7 billion years ago when an extremely dense concentration of mass rapidly expanded in an event known as the big bang.
(See related news: "Proof of Big Bang Seen by Space Probe, Scientists Say" [March 2006].)
The universe has been expanding ever since, so astronomers are able to age galaxies by computing how much the wavelength of their light has stretched—or redshifted—as the expansion takes the galaxies farther from Earth.
The redder the light is, the older and more distant the galaxy.
(See National Geographic magazine's "Beyond the Big Bang.")
The detection of such ancient galaxies adds intrigue to theories of how the very first galaxies formed, according to astronomers.
Were there many large, young galaxies in the early universe that are obscured from astronomers' view by abundant gases absorbing their light?
Or were galaxies rare and small way back then, as a prevailing theory suggests, and later clumped together to form larger galaxies such as the Milky Way?
"We believe that we need both these processes to explain what we see," Masanori Iye, a professor at the National Astronomical Observatory of Japan, said in an email.
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