Did Expelled Stars Reionize the Ancient Universe?
In the beginning there was light—the brilliant light of the big bang shining through a sea of protons, neutrons and electrons. But as the universe expanded and cooled, the electrons joined the protons, making neutral hydrogen atoms, and as the universe cooled further, the light went dark. Eventually, however, something tore the electrons from the protons, thereby re-ionizing the universe. Space has remained ionized—a plasma of positive ions and electrons—ever since. Now an upcoming paper in The Astrophysical Journal proposes the surprising cause: runaway stars flung from their galactic birthplaces.
“Re-ionization was one of the major cataclysmic events in the history of the universe,” says Charlie Conroy, an astronomer at the University of California, Santa Cruz. Yet because re-ionization occurred so long ago, even the greatest telescopes struggle to probe this distant epoch. Observations of the farthest quasars as well as the big bang’s afterglow indicate that re-ionization took place sometime between a redshift of 6 and 12, a measure of astronomical distance that corresponds to the time when the universe was only 380 million to 960 million years old. But exactly what caused this great transformation is a mystery.