Spectrum of Gamma-Ray Burst’s Afterglow Indicates the Beginning of the Re-ionization Process
A research team, led by professor Tomonori Totani (School of Science, the University of Tokyo) and composed of scientists from the National Astronomical Observatory of Japan, the Tokyo Institute of Technology and others, has discovered an indicator of when re-ionization of the primordial Universe began. The team used the Faint Object Camera and Spectrograph (FOCAS) mounted on the Subaru Telescope to thoroughly study the visible wavelength spectrum of the afterglow of a gamma-ray burst (GRB), which is a violent explosion of a massive star. Direct measurement of the absorption features in the spectrum of the afterglow toward GRB 130606A, located at the great distance, revealed the proportion of neutral hydrogen gas absorbing the light in its vicinity. This finding provides the best estimate of the amount of such neutral gas in the early Universe. The team’s research means that scientists can now narrow down the time when the Universe was beginning to re-ionize after its dark age.