NASA's Hubble Space Telescope has revealed that powerful winds from exploding stars may actually block ultraviolet radiation from escaping galaxies, challenging a widely accepted theory about how the early universe became transparent.
An international team including researchers from the University of Michigan examined nearby starburst galaxies using Hubble to study how ionizing radiation escapes. By analyzing light spectra, they measured galactic wind speeds and compared them to the amount of ultraviolet radiation leaving each galaxy. The team found that galaxies with the fastest winds allowed the smallest fraction of ionizing radiation to escape. This contradicts the leading explanation, which predicted that stronger winds should clear pathways for radiation to reach intergalactic space.
"Basically, how these galaxies were leaking ionizing radiation isn't what we thought," said Cody Carr, a postdoctoral researcher in the University of Michigan's Department of Astronomy who led the research.
The findings, published in Nature Astronomy, address one of the most important transformations in cosmic history. About 13 billion years ago, during reionization, radiation from early galaxies stripped electrons from neutral hydrogen atoms filling intergalactic space. This process made the universe transparent to ultraviolet light.
The research suggests that radiation from young, massive stars may escape their galaxies before those stars explode as supernovae. Energy from supernovae appears to redistribute gas and dust in ways that suppress radiation escape rather than clearing pathways for it.
"Our observations show that these photons are escaping before galactic winds form," Carr said.
Stephan McCandliss, a senior author and director of the Center for Astrophysical Sciences at Johns Hopkins University, noted that the findings suggest astronomers need to focus more on early star formation processes. Renyue Cen, a senior author and professor at Zhejiang University, added that the discovery highlights the need to examine how radiation and winds from young stars shape surrounding gas before the first supernovae explode.
Carr and colleagues are seeking additional Hubble observing time to examine more galaxies and test whether these patterns appear elsewhere.