"It seems like a viable hypothesis that these runaway stars can contribute significantly to the ionizing radiation," says Brian Siana of the University of California, Riverside. "But the question is: Are they the dominant factor?" Siana says supernova explosions may have punched holes in the gas of the first galaxies, producing a Swiss cheese–like structure that allowed extreme ultraviolet radiation from hot stars to seep out of the galaxies, obviating the need for runaways.
Conroy and Kratter suggest a way to test their idea. Astronomers can't see individual stars at the great distances corresponding to the epoch of re-ionization. But if hot stars escaped the first galaxies, the galaxies themselves should look larger at wavelengths where they emitted ultraviolet light than at longer wavelengths, because the hot, ultraviolet-bright runaway stars had fled their homes. Seeing such distant galaxies is too tough a task even for the Hubble Space Telescope, but Conroy and Kratter say that 30-meter ground-based telescopes planned for the future should find them, shedding new light on the universe's ancient metamorphosis.