WASHINGTON, D.C.--Astronomers have caught the moment at which the first stars blazed into life. New images of microwave radiation, taken by a NASA satellite, imply that the cosmos was swarming with activity much earlier than previously thought. And that could have implications for the role of dark matter in ordering the cosmos.
For the past few years, astronomers have been taking very fine measurements of the cosmic microwave background (CMB), microwave radiation left over from the hot, dense universe just 400,000 years after the big bang. Cosmologists have used these measurements to figure out the budget of matter and energy in the universe, as well as its age. But it was hard to nail it down firmly with data from only small slices of the sky.
At a press briefing today at NASA headquarters here, scientists released the first whole-sky measurement of the CMB from the Microwave Anisotropy Probe (MAP), a $145 million satellite launched in June 2001. The MAP map also provides the tightest bounds yet upon the age of the universe (13.7 billion years, give or take 1%). The satellite also measured the polarization of the CMB, just as the DASI instrument did late last year (ScienceNOW, 20 September 2002), but because MAP has a view of the entire sky, it was able to pick out much larger features.
These features tell of key events in the early universe. By studying the polarization of the CMB at large scales, the team could estimate when the light from newborn stars wrenched the electrons from free-floating atoms of neutral hydrogen. This "reionization" burned away the hydrogen fog that suffused the universe and marked the beginning of the modern era of stars and galaxies. According to the MAP findings, this happened about 200 million years after the big bang, much earlier than other analyses suggested.
The early dawn might be possible if an early population of massive stars sprang to life before quasars and galaxies began to form in earnest. If so, this prospect all but eliminates the possibility that fast-moving, "hot," dark matter played a role in the formation of structure in the universe. "This has profound consequences, I think," says Max Tegmark, a cosmologist a the University of Pennsylvania in Philadelphia. "On one hand, it's sort of shocking, on the other hand it's like a piece of the puzzle has fallen into place and you say, 'Aha!'"