This one is related to Big Bang... 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. 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.


The first stars that formed were probably 30 to 300 times more massive than the sun and millions of times as bright, burning for only a few million years before exploding. The energetic ultraviolet light from these stars was capable of splitting hydrogen atoms back into electrons and protons, thus ionizing them. Scientists believe that during reionization, the first galaxies to form ionized “bubbles” in the neutral gas surrounding them. Electrons in these bubbles would scatter with light particles from the cosmic microwave background. This would create small hot and cold spots in the CMB depending on whether a bubble is moving toward or away from Earth. A longer epoch of reionization would create more bubbles, leading to a larger signal in the CMB.



Latest results suggest that the epoch of reionization lasted less than 500 million years and began when the universe was at least 250 million years old. Before this measurement, scientists believed that reionization lasted 750 million years or longer, and had no evidence as to when reionization began. The epoch’s short duration indicates that reionization was more explosive than scientists had previously thought. It suggests that massive galaxies played a key role in reionization, because smaller galaxies would have formed much earlier. Rapid reionization also argues against many proposed astrophysical phenomena that would slow the process. 


This is only the beginning of what astronomers expect to learn about reionization from the South Pole Telescope. The current results are based on only the first third of the telescope’s full survey. Additional work is under way to combine South Pole Telescope maps with ones made by the Herschel satellite to further increase sensitivity to the reionization signal. It is expected to measure the duration of reionization to within 50 million years with the current survey.



Credits: University of Chicago