The Lyman-apha light from JADES-GS-z13-1 has taken nearly 13.47 billion years to reach us, as it dates back to just 330 million years after the Big Bang.
This image shows JADES-GS-z13-1 (the red dot at center), imaged with Webb’s Near-Infrared Camera (NIRCam) as part of the JADES program. Image credit: NASA / ESA / CSA / Webb / STScI / JADES Collaboration / Brant Robertson, UC Santa Cruz / Ben Johnson, CfA / Sandro Tacchella, Cambridge / Phill Cargile, CfA / J. Witstok, P. Jakobsen & A. Pagan, STScI / M. Zamani, ESA & Webb.
A key science goal of the NASA/ESA/CSA James Webb Space Telescope has been to see further than ever before into the distant past of our Universe, when the first galaxies were forming after the Big Bang.
This search has already yielded record-breaking galaxies, in observing programs such as the JWST Advanced Deep Extragalactic Survey (JADES).
Webb’s extraordinary sensitivity to infrared light also opens entirely new avenues of research into when and how such galaxies formed, and their effects on the Universe at the time known as cosmic dawn.
Astronomers studying one of those very early galaxies have now made a discovery in the spectrum of its light, that challenges our established understanding of the Universe’s early history.
JADES-GS-z13-1 (GS-z13-1 for short) was discovered in images taken by Webb’s NIRCam (Near-Infrared Camera) as part of the JADES program.
Dr. Roberto Maiolino from the University of Cambridge and University College London and colleagues used the galaxy’s brightness in different infrared filters to estimate its redshift, which measures a galaxy’s distance from Earth based on how its light has been stretched out during its journey through expanding space.
The NIRCam imaging yielded an initial redshift estimate of 12.9. Seeking to confirm its extreme redshift, the astronomers then observed the galaxy using Webb’s Near-Infrared Spectrograph (NIRSpec) instrument.
In the resulting spectrum, the redshift was confirmed to be 13.0. This equates to a galaxy seen just 330 million years after the Big Bang, a small fraction of the Universe’s present age of 13.8 billion years old.
But an unexpected feature stood out as well: one specific, distinctly bright wavelength of light, identified as the Lyman-alpha emission radiated by hydrogen atoms.
This emission was far stronger than astronomers thought possible at this early stage in the Universe’s development.
“The early Universe was bathed in a thick fog of neutral hydrogen,” Dr. Maiolino said.
“Most of this haze was lifted in a process called reionization, which was completed about one billion years after the Big Bang.”
“GS-z13-1 is seen when the Universe was only 330 million years old, yet it shows a surprisingly clear, telltale signature of Lyman-alpha emission that can only be seen once the surrounding fog has fully lifted.”
“This result was totally unexpected by theories of early galaxy formation and has caught astronomers by surprise.”
“Before and during the epoch of reionization, the immense amounts of neutral hydrogen fog surrounding galaxies blocked any energetic ultraviolet light they emitted, much like the filtering effect of colored glass.”
“Until enough stars had formed and were able to ionize the hydrogen gas, no such light — including Lyman-alpha emission — could escape from these fledgling galaxies to reach Earth.”
“The confirmation of Lyman-alpha radiation from this galaxy, therefore, has great implications for our understanding of the early Universe.”
“We really shouldn’t have found a galaxy like this, given our understanding of the way the Universe has evolved,” said University of Arizona astronomer Dr. Kevin Hainline.
“We could think of the early Universe as shrouded with a thick fog that would make it exceedingly difficult to find even powerful lighthouses peeking through, yet here we see the beam of light from this galaxy piercing the veil.”
“This fascinating emission line has huge ramifications for how and when the Universe reionized.”
The source of GS-z13-1’s Lyman-alpha radiation from this galaxy is not yet known, but it is may include the first light from the earliest generation of stars to form in the Universe.
“The large bubble of ionized hydrogen surrounding this galaxy might have been created by a peculiar population of stars — much more massive, hotter and more luminous than stars formed at later epochs, and possibly representative of the first generation of stars,” said Dr. Joris Witstok, an astronomer at the University of Cambridge and the University of Copenhagen.
“A powerful active galactic nucleus (AGN), driven by one of the first supermassive black holes, is another possibility identified by our team.”
The team’s findings were published in the March 26 issue of the journal Nature.
_____
J. Witstok et al. 2025. Witnessing the onset of reionization through Lyman-α emission at redshift 13. Nature 639, 897-901; doi: 10.1038/s41586-025-08779-5
