Analysis of data from the National Science Foundation’s South Pole Telescope, for the first time, more precisely defines the period of cosmological evolution when the first stars and galaxies formed and gradually illuminated the universe. The data indicate that this period, called the epoch of reionization, was shorter than theorists speculated — and that it ended early.
“We find that the epoch of reionization lasted less than 500 million years and began when the universe was at least 250 million years old,” said Oliver Zahn, a postdoctoral fellow at the Berkeley Center for Cosmological Physics at the University of California, Berkeley, who led the study. “Before this measurement, scientists believed that reionization lasted 750 million years or longer, and had no evidence as to when reionization began.”
The findings by Zahn, his colleagues at UChicago's Kavli Institute for Cosmological Physics and elsewhere have been published in a pair of papers appearing in the Sept. 1, 2012 issue of the Astrophysical Journal. Their latest results are based on a new analysis that combines measurements taken by the South Pole Telescope at three frequencies, and extends these measurements to a larger area covering approximately 2 percent of the sky. The 10-meter South Pole Telescope operates at millimeter wavelengths to make high-resolution images of the cosmic microwave background, the light left over from the big bang.
“Studying the epoch of reionization is important because it represents one of the few ways by which we can study the first stars and galaxies,” said study co-author John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics.
Before the first stars formed, most matter in the universe took the form of neutral hydrogen atoms. The radiation from the first stars transformed the neutral gas into an electron-proton plasma. Observations with the Wilkinson Microwave Anisotropy Probe satellite of polarized signals in the CMB indicate that this epoch occurred nearly 13 billion years ago, but these observations give no indication of when the epoch began or how long it lasted.