New data from the Hubble Space Telescope published on October 15, 2026, in Nature Astronomy challenges long-standing assumptions about cosmic reionization, revealing that supernova-driven galactic winds actually trap ultraviolet radiation rather than clearing paths for it to escape into the early universe.
For the first billion years after the Big Bang, a dense fog of neutral hydrogen blocked ultraviolet light from traveling freely across space. Astronomers have long sought to understand how high-energy Lyman continuum photons eventually punched through that opacity to clear the cosmos into the transparent universe observed today. The prevailing model relied on a straightforward mechanism: explosions from massive stars created galactic winds that acted like snowplows, clearing clean channels through interstellar gas and dust.
Observations of nearby compact starburst galaxies, which serve as local laboratories for conditions in the early universe, turned that hypothesis upside down. An international research team utilized the Hubble Space Telescope to measure Doppler shifts in spectral absorption lines, tracing both outflow velocities and the wavelengths of light escaping the systems.
How Supernova Winds Obstruct Ultraviolet Light in Starburst Galaxies
Instead of carving out clear escape routes, powerful stellar outflows compound the obstruction. Energy deposited by supernovae stirs up the surrounding environment, increasing the density and coverage of neutral hydrogen and dust rather than blasting them 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.
The research team found a strong negative correlation between outflow velocity and the fraction of escaping radiation. Galaxies with the fastest, most mass-loaded winds permitted the smallest fraction of ultraviolet light to leak out. This discovery points toward an alternative scenario where high-energy photons escaped from young, massive stars before supernova detonations generated winds powerful enough to disrupt their host galaxies.
Refining Cosmological Simulations at Zhejiang University and Johns Hopkins
The findings carry direct consequences for how researchers model the epoch of reionization. Cosmological hydrodynamic simulations have traditionally relied on supernovae as the primary driver for radiation escape.
Supernovae play a central role in cosmological hydrodynamic simulations that explain how ionizing radiation escapes from galaxies.
Those models must now account for early radiative feedback and local stellar winds operating before major supernova activity begins. Carr, who led the study as a postdoctoral scholar at Zhejiang University before joining U-M, noted that the exact populations of early galaxies responsible for reionization and the precise mechanics of how photons leaked remain incompletely understood.
Scientists Seek More Hubble Time to Test Radiation
The published research involved an international collaboration of nearly 30 scientists across more than a dozen institutions, including contributions from Sally Oey of the University of Michigan.
To test whether radiation escapes preferentially before powerful winds develop, the research team is seeking additional observing time with Hubble. The observatory recently marked its 200,000th orbit around Earth on September 19 after traveling more than 5 billion miles over 36 years.