Hubble Space Telescope observations of nearby starburst galaxies reveal that powerful supernova-driven winds trap ultraviolet radiation rather than helping it escape. Published in Nature Astronomy on October 15, 2026, the findings challenge long-held theories about cosmic reionization and suggest early young stars played a more direct role. Marking another new milestone for an observatory that continues to transform our understanding of the universe, Hubble completed its 200,000th orbit around Earth on Sept. 19, as noted by science.nasa.gov. Over its 36-year lifetime, Hubble has traveled more than 5 billion miles around Earth and exceeded 1.7 million total observations, according to science.nasa.gov.
For years, astronomers trying to understand the universe’s last major phase transition leaned on a straightforward explanation. During the first billion years, neutral hydrogen formed an opaque fog that blocked ultraviolet light. Radiation from early galaxies eventually ionized that hydrogen, clearing the intergalactic medium. A leading explanation proposed that supernovae cleared paths for ionizing radiation to leave early galaxies, acting as cosmic snowplows that blasted away surrounding gas.
New data from the Hubble Space Telescope turned that assumption around. Researchers examining compact starburst galaxies found that galaxies with the fastest winds actually permitted the smallest fraction of ultraviolet radiation to escape.
How Supernova Winds Trap Radiation in Starburst Galaxies
Starburst galaxies form stars at unusually rapid rates, serving as useful local laboratories for conditions that may have existed in early reionizing galaxies. The research team utilized spectra from Hubble to measure both the wavelengths of light escaping these compact systems and the velocities of their outflows. Neutral hydrogen and dust in the outflowing gas absorb ultraviolet light at characteristic wavelengths, creating spectral dips whose positions and widths reveal how the gas moves.
Rather than clearing escape routes, powerful winds appear to compound the obstruction. Energy deposited by supernovae stirs the surrounding environment, increasing the coverage of neutral hydrogen and dust meant to be cleared away.
It appears that energy input from supernovae has stirred up the surroundings and increased, rather than decreased, the coverage of neutral gas and dust that suppresses ionizing radiation escape.
Stephan McCandliss, senior author of the study and director of the Center for Astrophysical Sciences at Johns Hopkins University
Radiation Escapes Young Stars Before Supernovae Reshape Galaxies
The findings point toward an alternative scenario where radiation escaped from young stars before supernova explosions generated winds powerful enough to reshape their host galaxies. Cody Carr, a postdoctoral researcher in the University of Michigan Department of Astronomy who led the study while at Zhejiang University, noted that while astronomers know reionization occurred, the exact mechanisms by which photons escaped remain incompletely understood.
Supernovae play a central role in cosmological hydrodynamic simulations that explain how ionizing radiation escapes from galaxies.
Renyue Cen, senior author and professor and director of Zhejiang University’s Center for Cosmology and Computational Astrophysics
Renyue Cen added that the discovery highlights a need to examine how radiation and winds from young stars shape surrounding gas before the first supernovae explode.
International Team Uses Hubble for Published Research
The published research involved an international team of nearly 30 collaborators across more than a dozen institutions, with contributions from Sally Oey of the University of Michigan. Hubble itself was developed by NASA with contributions from the European Space Agency, while the Space Telescope Science Institute administered a grant supporting the work. Highlighting Hubble’s enduring productivity, science.nasa.gov reports that astronomers request about seven times as much observing time as is available each year, drawn to instruments whose ultraviolet and visible wavelength capabilities complement NASA’s James Webb and Roman Space Telescopes.
While the study narrows uncertainties surrounding the physics of ionizing radiation escape, it does not identify the precise population of early galaxies responsible for reionization or establish a complete timeline for the process. To push further, the research team is seeking additional Hubble observing time. They aim to study more galaxies to test whether radiation escapes preferentially before powerful supernova-driven winds develop.
