A local clue to the reionization of the universe

Identifying the population of galaxies that was responsible for the reionization of the universe is a long-standing quest in astronomy. We present a possible local analog that has an escape fraction of ionizing flux of 21%. Our detection confirms the existence of gaps in the neutral gas enveloping the starburst region. The candidate contains a massive yet highly compact star-forming region. The gaps are most likely created by the unusually strong winds and intense ionizing radiation produced by this extreme object. Our study also validates the indirect technique of using the residual flux in saturated low-ionization interstellar absorption lines for identifying such leaky galaxies. Because direct detection of ionizing flux is impossible at the epoch of reionization, this represents a highly valuable technique for future studies. A compact starburst galaxy is identified as an analog to those that reionized the early universe with energetic starlight. A light leak to transform the universe After the universe had cooled into an expanse of neutral gas after the Big Bang, how did the first starlight emerge from the dark? Borthakur et al. found a local starburst galaxy that leaks continuum radiation, which may provide some clues. Wind-generated gaps in the neutral gas enable large fractions of ionizing radiation to escape, possibly mimicking processes in the early universe. Science, this issue p. 216