For years, astronomers have told a dramatic story about how the early universe cleared. Exploding stars, the thinking went, blasted holes in galaxies and let light escape. A new Hubble study suggests the opposite: galaxies with the fastest winds let out the least light. If that holds up, young stars may deserve much of the credit.
Why it matters: this was the last great change in the universe’s history, and it’s why we can see across space at all. Knowing what drove it tells us how the first galaxies shaped everything that followed.
The cosmic fog
After the Big Bang, space filled with neutral hydrogen gas, a kind of fog that blocked ultraviolet light. Around 13 billion years ago, radiation from the first stars and galaxies stripped electrons from that gas, in a change called reionization. The universe turned transparent.
The puzzle is how the radiation got out of its home galaxies, which were full of gas themselves. The leading idea was that supernova explosions drove powerful winds that cleared a path.
What Hubble found
Nobody can watch that era directly in this detail, so the team, led by Cody Carr of the University of Michigan, used stand-ins. They studied six nearby star-forming galaxies at different ages, measuring how fast their winds blew and how much ionizing light got out.
The stronger the wind, the less light escaped. “Our observations show that these photons are escaping before galactic winds form,” Carr said.
The likely story now has two acts, as Universe Today explains. First, young stars and perhaps a few early supernovae open channels through the gas. Then, as more stars explode, they stir up gas and dust that block the light. Supernovae may have helped a little at the start, then got in the way.
How sure are they?
Not completely. Six galaxies is a small sample, and nearby galaxies are stand-ins, so applying this to the early universe is an inference. Computer simulations give supernovae a central role, and the new result conflicts with that. Smaller winds near young stars could also still matter.
What happens next
Carr’s team is seeking more Hubble time to check more galaxies. Simulations will also need another look at what young stars do to gas before the first explosions. It’s a lovely reminder that a 36-year-old telescope can still upset a good story.
Read next
- How the universe lit up after the Big Bang: Lumina simulation
- Webb spots a possible supernova just days after it exploded
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Sources
- Shining new light on the ‘last major phase transition in the universe’ – University of Michigan, October 2026
- Supernova explosions first aided, then later impeded, the Epoch of Reionization – Universe Today, October 2026
- Hubble reveals a stunning twist in how the universe emerged from darkness – ScienceDaily, October 2026
