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Hidden star factories in early universe found.

Some of the brightest galaxies in the universe--infant galaxies that churned out tens of thousands of stars each year at the dawn of the universe--evolved much sooner and in greater numbers than previously thought, according to new measurements obtained by astronomers. The research is the most recent example of the discoveries coming from the international ALMA observatory, which stands for Atacama Large Millimeter/submillimeter Array--66 radio telescopes located in the dry and cloudless Atacama Desert in Chile.

The most intense bursts of star birth are thought to have occurred in the early universe, in massive, bright galaxies. These starburst galaxies used to convert vast reservoirs of cosmic gas and dust into new stars at a furious pace--many hundreds of times faster than in stately spiral galaxies like our own Milky Way. By looking far into space, at galaxies so distant that their light has taken many billions of years to reach us, astronomers can observe this busy period in the universe's youth.

"Even though these galaxies are among the brightest objects in the universe, they are very hard to see with telescopes that detect visible light, such as the Hubble Space Telescope," explains Dan Marrone, assistant professor at the University of Arizona's Steward Observatory. The reason is that these young galaxies are enshrouded in thick clouds of dust. "Instead, we use ALMA to look for them in light coming from the dust itself. To ALMA, these are some of the brightest objects in the sky outside our own galaxy."

The researchers first discovered these distant and enigmatic starburst galaxies with the National Science Foundation's 10-meter South Pole Telescope and then used ALMA to zoom in on them to explore the stellar baby boom in the young universe. They were surprised to find that many of these distant, dusty star-forming galaxies are even farther away than expected. This means that, on average, their bursts of star birth took place 12,000,000,000 years ago, when the universe was just under 2,000,000,000 years old--a full 1,000,000,000 years earlier than previously thought.

Two of these galaxies are the most distant of their kind ever seen--so distant that their light began its journey when the universe was a mere 1,000,000,000 years old. One of them appears to host the most intense burst of star formation that ever has been seen. Water molecules also are detected in that same galaxy, marking the most-distant observations of water in the cosmos published to date.

The team used the unrivaled sensitivity of ALMA to capture light from 26 of these galaxies at wavelengths of around three millimeters. Molecules of carbon monoxide, a poisonous gas that also is the second-most abundant molecule in the universe, are created in the star-forming gas in these galaxies and emit light at certain specific wavelengths. These wavelengths are stretched by the expansion of the universe over the billions of years that it takes the light to reach Earth. By measuring the stretched wavelengths, astronomers can calculate how long the light's journey has taken, and place each galaxy at the right point in cosmic history.

"The sensitivity of ALMA allowed us to do in a few minutes per galaxy what used to require hours or even multiple nights," marvels Joaquin Vieira, postdoctoral scholar at the California Institute of Technology, Pasadena.

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Title Annotation:Outer Space
Publication:USA Today (Magazine)
Date:Dec 1, 2013
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