An international research team using NASA’s Hubble Space Telescope has discovered findings that challenge a widely accepted theory about how the early universe became transparent to ultraviolet light. Published in Nature Astronomy, the research suggests that powerful winds generated by exploding stars may interfere with the escape of ultraviolet radiation from galaxies, contrary to what scientists had previously believed.
During the first billion years after the Big Bang, neutral hydrogen filled the space between galaxies, creating a cosmic fog that blocked ultraviolet radiation. A period known as reionization, which began approximately 13 billion years ago, gradually transformed this hydrogen by ionizing it—stripping electrons from atoms to create free electrons and positively charged protons. This transformation allowed ultraviolet light to travel much farther through space and helped establish the relatively transparent universe observed today. However, astronomers have not fully understood which objects supplied the radiation responsible for reionization or how enough of that radiation managed to escape from early galaxies.
The prevailing explanation centered on supernovae, the powerful explosions occurring when certain stars reach the end of their lives. These explosions generate enormous winds that were thought to sweep through galaxies and clear pathways for ultraviolet radiation to escape into intergalactic space. However, Hubble’s new observations indicate this process may work in the opposite way. The research team examined nearby starburst galaxies—those experiencing exceptionally intense star formation—and found that galaxies with the fastest winds allowed the smallest fraction of ionizing radiation to escape. Rather than opening routes for radiation, the supernova winds appear to redistribute gas and dust in ways that suppress radiation escape.
The team studied the light spectra from these galaxies to determine wind speeds and compare them with the amount of ionizing radiation escaping each galaxy. The unexpected inverse relationship directly challenges the expectation that stronger winds would clear away more gas and make it easier for radiation to reach space. The findings suggest that radiation from young, massive stars may escape their galaxies before those stars explode as supernovae. Astronomers may need to focus greater attention on the earliest stages of star formation rather than primarily on the effects of exploding stars. The research team is seeking additional Hubble observations to examine more galaxies and investigate whether similar patterns appear elsewhere.
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