New observations from NASA’s Hubble Space Telescope have thrown a leading theory of the early universe into question. An international research team, including astronomers from the University of Michigan, found that powerful winds generated by exploding stars can prevent ultraviolet radiation from escaping galaxies, the opposite of what a widely accepted theory had predicted. The discovery, published in Nature Astronomy, could change how scientists understand reionisation, the period about 13 billion years ago when the universe emerged from its cosmic fog.
During the first billion years after the Big Bang, neutral hydrogen filled intergalactic space, absorbing ultraviolet light and preventing it from travelling freely. This cosmic fog began to lift during reionisation, when intense radiation from early galaxies stripped electrons from hydrogen atoms, allowing ultraviolet light to pass through. One prominent theory held that supernovae generated winds that cleared pathways through gas, enabling radiation to escape. But new Hubble data suggests the opposite.
“Basically, how these galaxies were leaking ionizing radiation isn’t what we thought,” said Cody Carr, a postdoctoral researcher at the University of Michigan who led the research while at Zhejiang University in China. The team examined nearby starburst galaxies using Hubble’s spectra to measure wind speeds and escaping radiation. They found that galaxies with the fastest winds allowed the smallest fraction of ionizing radiation to escape.
“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,” said Stephan McCandliss, a senior author of the study and director of the Center for Astrophysical Sciences at Johns Hopkins University. Instead of opening routes, energy from supernovae appears to redistribute gas and dust in ways that can block more ionizing radiation.
Carr and his colleagues suggest that radiation from young, massive stars may escape their galaxies before those stars explode as supernovae. “Our observations show that these photons are escaping before galactic winds form,” Carr said. The findings suggest astronomers may need to pay greater attention to the earliest stages of star formation to understand reionisation.
Renyue Cen, a senior author and professor at Zhejiang University, said supernovae play a central role in cosmological hydrodynamic simulations. “Supernovae play a central role in cosmological hydrodynamic simulations that explain how ionizing radiation escapes from galaxies. Our findings highlight the need to examine how radiation and winds from young stars shape the surrounding gas before the first supernovae explode.”
The team is seeking additional observing time with Hubble to study more galaxies and investigate whether the same patterns appear elsewhere. The research involved nearly 30 scientists from more than a dozen institutions and was supported by NASA, the National Science Foundation, and other funding bodies.
Analysis
Why This Matters
- The discovery challenges a key assumption about how the universe became transparent, potentially altering our understanding of a major phase in cosmic history.
- It shifts focus from supernovae to younger stars as the likely source of ionising radiation, which could change how astronomers model galaxy formation and evolution.
- The findings may prompt revisions to computer simulations of the early universe that have relied heavily on supernova-driven winds to explain radiation escape.
Background
Reionisation is the period roughly 13 billion years ago when neutral hydrogen in intergalactic space was ionised, allowing ultraviolet light to travel freely. It is considered the last major phase transition of the universe. Until now, a leading theory suggested that winds from supernova explosions cleared paths for ionising radiation to escape early galaxies, but direct evidence was lacking. The Hubble Space Telescope, a joint NASA-ESA mission, has provided the first detailed spectral observations of starburst galaxies that challenge that picture.
What to Watch
- Whether follow-up Hubble observations of additional galaxies confirm the same inverse relationship between wind speed and radiation escape.
- How cosmological simulations are revised to account for radiation escaping before supernovae explode.
- What the findings mean for determining the role of young stars in cosmic reionisation.
Checked
12 claims in this story checked against 1 source: 11 supported.
Show each claim
- SupportedSupernova-driven galactic winds may hinder ultraviolet radiation from escaping galaxies.Latest Science News -- ScienceDaily: “powerful winds produced by exploding stars can prevent ultraviolet radiation from escaping galaxies.”
- SupportedThe international team’s finding challenges a leading theory of cosmic reionisation.Latest Science News -- ScienceDaily: “This is the opposite of what a widely accepted theory had predicted”
- SupportedThe discovery could change scientists’ understanding of reionisation.Latest Science News -- ScienceDaily: “it could change how scientists understand one of the most important transformations in cosmic history.”
- Partly supportedReionisation was a period about 13 billion years ago when the universe emerged from its cosmic fog.Latest Science News -- ScienceDaily: “That changed during a period known as reionization, which began approximately 13 billion years ago.”
- SupportedCody Carr said, “Basically, how these galaxies were leaking ionizing radiation isn’t what we thought.”Latest Science News -- ScienceDaily: “"Basically, how these galaxies were leaking ionizing radiation isn't what we thought," Carr said.”
- SupportedThe team examined nearby starburst galaxies and found that those with the fastest winds let the smallest fraction of ionising radiation escape.Latest Science News -- ScienceDaily: “Galaxies with the fastest winds allowed the smallest fraction of ionizing radiation to escape.”
- SupportedStephan McCandliss said supernova energy increased, rather than decreased, neutral gas and dust coverage that suppresses radiation escape.Latest Science News -- ScienceDaily: “"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," said Stephan McCandliss”
- SupportedCarr and his colleagues suggest radiation from young, massive stars may escape before those stars explode as supernovae.Latest Science News -- ScienceDaily: “Radiation from young, massive stars may escape their galaxies before those stars explode as supernovae”
- SupportedCarr said, “Our observations show that these photons are escaping before galactic winds form.”Latest Science News -- ScienceDaily: “"Our observations show that these photons are escaping before galactic winds form," Carr said.”
- SupportedRenyue Cen said supernovae play a central role in cosmological hydrodynamic simulations and that the findings highlight the need to examine how young-star radiation and winds shape gas before the first supernovae.Latest Science News -- ScienceDaily: “"Supernovae play a central role in cosmological hydrodynamic simulations that explain how ionizing radiation escapes from galaxies," said Renyue Cen”
- SupportedThe team is seeking more Hubble observing time to study more galaxies and see whether the patterns appear elsewhere.Latest Science News -- ScienceDaily: “Carr and his colleagues are seeking additional observing time with Hubble to examine more galaxies and investigate whether the same patterns appear elsewhere.”
- SupportedThe research involved nearly 30 scientists from more than a dozen institutions and received support from NASA, the National Science Foundation and other funders.Latest Science News -- ScienceDaily: “The research brought together nearly 30 scientists from more than a dozen institutions around the world.”
