For hundreds of millions of years after the Big Bang, our universe was cloaked in a dense, obscuring fog of neutral gas. This primordial haze effectively hid the first stars and galaxies, swallowing their light and rendering the early cosmos a mystery. Now, thanks to the revolutionary James Webb Space Telescope (JWST), scientists have pierced this ancient veil, revealing what appears to be one of the universe’s earliest “sunny spots”—a clear bubble of gas created by a remarkably energetic galaxy that emerged just 330 million years after the universe began. This groundbreaking discovery offers an unprecedented look at how our universe transitioned from a state of primordial darkness to the transparent, star-filled expanse we see today.
This transformation period, known as the “Epoch of Reionization,” has long been a major puzzle in cosmic history. Before this era, the universe was dominated by neutral hydrogen gas, which readily absorbed the powerful ultraviolet (UV) light from newly forming stars and galaxies. This absorption meant that much of the early universe remained hidden. Astronomers theorized that as the first light sources ignited, their intense UV radiation would slowly break apart these neutral atoms, making the universe transparent. The central questions have always revolved around when this process truly began and what kind of cosmic engines were powerful enough to carve out these first clear pathways. This new research provides crucial insight into that very process.
Webb’s Breakthrough: Finding Ancient Light
The incredible sensitivity of the James Webb Space Telescope (JWST) made these observations possible. Researchers utilized JWST’s Near-Infrared Camera (NIRCam) and Near-Infrared Spectrograph (NIRSpec) as part of the JWST Advanced Deep Extragalactic Survey (JADES) and JADES Origins Field (JOF) programs. These programs conduct deep imaging and analyze the light signatures from the most distant parts of the universe.
The team embarked on a meticulous search for extremely distant galaxies, identifying a key candidate: JADES-GS-z13-1-LA. This galaxy stood out due to a distinctive “dropout” signature in specific NIRCam filters, indicating its light had been significantly absorbed by intervening neutral hydrogen. Its redshift, a measure of how much an object’s light has been stretched by the universe’s expansion (telling us its age and distance), placed it at a remarkable 13.0. This means we are seeing JADES-GS-z13-1-LA as it was only about 330 million years after the Big Bang.
To confirm this distant galaxy’s identity and pinpoint its exact redshift, powerful spectroscopic analysis was essential. JWST’s NIRSpec, using its PRISM mode and an extensive 18.7-hour exposure, captured the spectrum of JADES-GS-z13-1-LA. This detailed light signature unequivocally confirmed its redshift at approximately 13.0.
The Signal of a Clear Path: Lyman-alpha Emission
What made JADES-GS-z13-1-LA truly stand out among other extremely distant galaxies confirmed by JWST was the detection of a singular, bright emission line, identified as Lyman-alpha (Ly-α).
Ly-α is a specific type of ultraviolet light emitted when hydrogen atoms undergo a particular energy change. It’s a hallmark of star formation and energetic processes within galaxies. In the early, neutral universe, Ly-α photons were easily absorbed and scattered by the surrounding hydrogen fog. Thus, detecting Ly-α from such an incredibly early galaxy at redshift 13.0 was a significant surprise. Its presence suggests the galaxy is a powerful producer of “ionizing photons”—energetic particles of light capable of stripping electrons from neutral hydrogen atoms, thereby “ionizing” the gas and making it transparent.
This unexpected Ly-α emission, combined with the galaxy’s unusually blue UV light signature, strongly implies that JADES-GS-z13-1-LA carved out an “early reionized region”—essentially punching a hole through the dense cosmic fog around itself. Without such a clear pathway, the Ly-α light would have been entirely absorbed and unable to reach the JWST. This “ionized bubble” around JADES-GS-z13-1-LA is estimated to be roughly 0.2 physical megaparsecs (pMpc) in radius, which translates to about 650,000 light-years across. It’s a significant patch of cleared space in the otherwise murky early universe.
Joris Witstok, a lead researcher on the study, elaborates, “We believe that we have discovered one of the first such bubbles.”
What Powered This Cosmic Clear-Out?
The immediate question from this discovery revolves around the powerful source within JADES-GS-z13-1-LA that created this massive ionized bubble and emitted such strong Ly-α. Researchers explored two primary possibilities:
One explanation is that the galaxy contained a population of incredibly hot and massive early stars. These could be the theoretical “Population III (Pop III) stars,” the universe’s first-generation stars, composed only of the lightest elements forged in the Big Bang. These stars are predicted to be far more massive and hotter than any stars we see today, making them tremendous producers of UV light and ionizing photons. Their existence could account for the high efficiency of ionizing photon production inferred from the observations. However, for JADES-GS-z13-1-LA to be a pure Pop III system, models indicate it would need a slightly higher stellar mass than typically predicted. Additionally, the lack of strong emission from another element, Helium II, could complicate a pure Pop III scenario, though the intensity of this emission changes rapidly after a star-forming burst.
The other compelling possibility is that the galaxy hosts a central, actively feeding supermassive black hole, known as an Active Galactic Nucleus (AGN). Joris Witstok further explains, “Most galaxies are known to host a central, supermassive black hole. As these monsters engulf surrounding gas, the gas is heated to millions of degrees, making it shine brightly in X-rays and UV before disappearing forever. This is another viable cause of the bubbles, which we will now investigate.” AGNs are known for their high “escape fractions” for ionizing light and can produce the kind of broad Ly-α lines observed. The galaxy’s compact size, with a half-light radius of less than 35 parsecs (about 114 light-years), is smaller than most other distant galaxies and aligns well with the characteristics of an AGN. While an AGN doesn’t rule out massive stars contributing, it provides a powerful alternative or complementary explanation for the observed properties. It’s also worth noting that specific geometric arrangements within the galaxy could have allowed the Ly-α light to escape, for instance, if the galaxy had a clear pathway for light perpendicular to its disk.
A New Chapter in Cosmic History
Peter Jakobsen, affiliated professor at DAWN, project scientist for JWST’s spectrograph NIRSpec, and a co-author of the study, shares his perspective: “We knew that we would find some of the most distant galaxies when we built Webb. But we could only dream of one day being able to probe them in such detail that we can now see directly how they affect the whole Universe.”
This discovery significantly advances our understanding of the early universe. The detection of Ly-α emission from JADES-GS-z13-1-LA at such an incredibly early epoch provides concrete evidence that cosmic reionization began earlier and was a more gradual process than previously believed. This finding suggests the universe wasn’t just waiting for the biggest, brightest galaxies to switch on; even relatively “UV-faint” sources like JADES-GS-z13-1-LA played a vital role in clearing the cosmic fog. This finding is like witnessing the very first rays of sunlight piercing through a dense morning mist, illuminating the landscape for the first time. It reshapes our understanding of how quickly the early universe transformed and provides vital constraints on the timeline of cosmic reionization. The cosmic dark ages are slowly but surely being unveiled, revealing a universe that began illuminating itself remarkably early, paving the way for the stars and galaxies we see twinkling above us today.
Paper Summary
Methodology
The research utilized the James Webb Space Telescope (JWST), specifically its Near-Infrared Camera (NIRCam) and Near-Infrared Spectrograph (NIRSpec), as part of the JADES and JOF programs. A high-redshift galaxy candidate, JADES-GS-z13-1-LA (redshift z ≥ 11.5), was identified through NIRCam imaging. Its redshift was precisely confirmed at ~13.0 via 18.7-hour spectroscopic observations with NIRSpec in PRISM mode.
Results
A bright Lyman-alpha (Ly-α) emission line was detected from galaxy JADES-GS-z13-1-LA at redshift 13.0 (330 million years after the Big Bang). This indicates the galaxy is a significant producer of ionizing photons, creating an “ionized bubble” of approximately 0.2 physical megaparsecs (pMpc) around itself. The findings suggest this reionized region was formed by either massive, hot stars or an active galactic nucleus (AGN).
Limitations
Current stellar population models do not fully account for the observed Ly-α emission profile. While very massive stars are a possibility, the lack of strong Helium II emission may argue against a pure Population III star scenario. However, the data remains consistent with predictions for metal-poor AGNs.
Funding/Disclosures
Specific funding sources or financial disclosures were not detailed in the provided document snippets. The paper indicates that acknowledgements, peer review information, author contributions, competing interests, and data/code availability are accessible via the provided DOI.
Paper Publication Information
Title: Witnessing the onset of reionization through Lyman-α emission at redshift 13 Authors: Joris Witstok et al. Journal: Nature Volume: 639 Page Numbers: 897-900 DOI: https://doi.org/10.1038/s41586-025-08779-5 Received: 30 August 2024 Accepted: 12 February 2025 Published Online: 26 March 2025
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