Word: hydrogen
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Dates: during 2000-2009
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What makes Mileura and the other projects so powerful is that by tuning the receivers to different radio frequencies, they will be able to pick up signals broadcast by hydrogen atoms at different periods in the Dark Ages. When you map cosmic hydrogen at, say, 50 million years after the Big Bangbefore the first stars had a chance to formthen at 100 million, 200 million or half a billion years later, you get a series of snapshots. Combine them, says Loeb, and "you'll be able to make a 3-D picture of hydrogen gas as the universe evolves...
...young galaxies. The Sloan Digital Sky Survey, a comprehensive scan of the heavens, has turned up several of these from about a billion years after the Big Bang. By watching how the light of quasars is altered by surrounding gas, astronomers have concluded that there was still some atomic hydrogen around then, although not much...
...WMAP satellite, launched to look for light left from the Big Bang using a broadly analogous technique, determined the clearing out of hydrogen between the stars was well under way much earlier, just half a billion years post--Big Bang. "Theorists have been telling us that it should have happened fairly quickly once it began," says Michael Strauss, a Princeton University astronomer and deputy project scientist for the Sloan survey. "But the observations may be telling us otherwise...
...DARK MATTER Accounting for a bigger portion of matter than ordinary atoms, dark-matter particles were spread unevenly through the cosmos; areas of higher concentration drew in hydrogen and helium gas, gradually forming the first stars dense enough to burst into thermonuclear flame 3 FIRST STARS The earliest stars were massive, weighing in at 20 to more than 100 times the mass of the sun. The crushing pressures at their cores made them burn through their nuclear fuel in only a million years or so and caused them to spew radiation so intense that it kept other stars from forming...
...DARK AGES The death of the mega-stars triggered the formation of normal stars, creating the first recognizable dwarf galaxies. Their radiation in turn burned through the remaining shrouds of hydrogen, bringing the dark ages to a close TIME Graphic by Joe Lertola Sources: Professor Avi Loeb, Harvard University; Professor Richard Ellis, Caltech...