Plate Nº 24 · recorded October 30, 2026
Space & AstronomyReported finding
Hubble finds stellar winds can suppress escaping ultraviolet light
Hubble observations show that faster galactic winds let less ultraviolet radiation escape starburst galaxies, suggesting young stars, not supernova blasts, may have cleared the universe's hydrogen fog.
By Priya Raman5 min read998 words
In brief
- During the universe's first billion years, neutral hydrogen filled space between galaxies and absorbed ultraviolet light.
- Reionization began approximately 13 billion years ago and transformed neutral hydrogen into electrically charged hydrogen.
- In the observed starburst galaxies, the fastest galactic winds corresponded to the smallest fraction of escaping ionizing radiation.
- Nearly 30 scientists from more than a dozen institutions took part in the research.
- The study appeared in Nature Astronomy in 2026; the University of Michigan released the results on October 30, 2026.
By Priya Raman
About 13 billion years ago, early galaxies began helping ultraviolet light escape a hydrogen-filled cosmic fog; Hubble observations now show that powerful stellar winds can block that escape, challenging a leading theory.
Cody Carr, a postdoctoral researcher in the University of Michigan Department of Astronomy, led an international team using NASA’s Hubble Space Telescope to examine nearby starburst galaxies, systems undergoing exceptionally intense star formation. The team found that the fastest galactic winds allowed the smallest fraction of ionizing radiation—ultraviolet light energetic enough to remove electrons from hydrogen atoms—to escape.
Stephan McCandliss, a senior author of the study and director of Johns Hopkins University’s Center for Astrophysical Sciences, said:
“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.”
Stellar explosions, in other words, spread more gas and dust across the path instead of clearing it. The timing of the radiation points toward a possible sequence: ultraviolet photons—individual packets of light energy—may escape while young, massive stars remain alive, before supernova winds reshape their surroundings.
Carr said:
“Our observations show that these photons are escaping before galactic winds form.”
How did the universe shed its cosmic fog?
During the first billion years after the Big Bang, vast amounts of neutral hydrogen filled the space between galaxies. These atoms absorbed ultraviolet radiation, preventing the light from traveling freely through the universe.
Beginning approximately 13 billion years ago, intense radiation from early galaxies stripped electrons from hydrogen atoms, leaving positively charged protons and free electrons. Astronomers call this transformation reionization, a process that made hydrogen ionized, or electrically charged.
As more hydrogen became ionized, ultraviolet light could travel much farther through intergalactic space. The change helped establish the relatively transparent universe that telescopes observe today. Carr described reionization as the universe’s last major phase transition.
The team knows the transition occurred, but it lacks complete answers about which objects supplied the radiation and how enough of it escaped from early galaxies.
Why did the supernova-wind explanation fail?
For years, a prominent explanation centered on supernovae, the powerful explosions that mark the end of certain stars’ lives. These events can drive galactic winds, outward flows of gas that push material away from a galaxy’s center.
Scientists proposed that the winds cleared pathways through gas around young stars. Once ultraviolet radiation escaped into the space between galaxies, it could break apart neutral hydrogen and help remove the ancient fog.
The Hubble observations reveal the opposite relationship. Stronger winds accompany less escaping ionizing radiation. Energetic outflows redistribute gas and dust so that more neutral material covers the route and suppresses the light.
What did Hubble measure?
Hubble, a NASA mission launched with contributions from the European Space Agency, let the team study the light from these galaxies in detail. The researchers used nearby starburst galaxies as modern examples of the kinds of galaxies astronomers believe contributed to reionization.
They examined each galaxy’s spectrum, the pattern of light across different wavelengths. Gas absorbs particular wavelengths and creates recognizable dips in that pattern. The positions and shapes of the dips reveal how quickly the surrounding gas moves.
The team compared those inferred wind speeds with the amount of ionizing radiation escaping from each galaxy. Galaxies with the fastest winds allowed the smallest fraction of radiation to escape, directly contradicting the expectation that stronger winds would clear more gas.
Could young stars have opened the path?
Large galactic winds appear to suppress escaping radiation. Smaller winds and other activity around young stars could still create openings in the surrounding gas, and those processes may begin before the first supernova explosions.
The findings suggest that astronomers may need to place greater emphasis on the earliest stages of star formation rather than concentrating mainly on exploding stars. Carr and his colleagues are seeking additional Hubble observing time to study more galaxies and test whether the pattern appears elsewhere.
More observations could establish how much young-star activity contributes to radiation escape. The study does not identify which objects caused reionization, and examining nearby galaxies rather than ancient ones leaves uncertainty. The result therefore narrows the possibilities without settling the larger question.
How will simulations change?
Cosmological hydrodynamic simulations, computer models that recreate how galaxies formed and how gas and radiation moved through them, often give supernovae a central role in explaining radiation escape.
Renyue Cen, a senior author and professor who directs Zhejiang University’s Center for Cosmology and Computational Astrophysics, said the findings require models to examine how radiation and winds from young stars shape surrounding gas before the first supernovae explode. More accurate treatment of those early interactions may improve reconstructions of reionization.
Who carried out the research?
Nearly 30 scientists from more than a dozen institutions around the world took part. Carr conducted and led the research while a postdoctoral scholar at Zhejiang University in China before joining the University of Michigan. Sally Oey, a professor of astronomy at the University of Michigan, also contributed.
Additional support for the project included:
- Zhejiang University and the Zhejiang Provincial Top-Level Research Support Program.
- The National Natural Science Foundation of China.
- The Ministry of Science, Innovation and Universities in Spain, the European Regional Development Fund, and the European Union’s Horizon 2020 Research and Innovation Program.
- Federal research funding from NASA and the U.S. National Science Foundation.
- A Space Telescope Science Institute grant that supported additional Hubble observations.
The paper, “Lyman continuum escape during the onset of galactic winds in compact starbursts,” appeared in Nature Astronomy in 2026. The title refers to the escape of the ionizing radiation the team measured. Its DOI is 10.1038/s41550-026-02999-z, and the University of Michigan released the results on October 30, 2026.
The immediate conclusion is measured but consequential: the universe may have become transparent before supernova winds made radiation’s escape harder.
via dx.doi.org (Original)
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Senior reporter covering people, launches and day-to-day practice in general science news at SciBeat.
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