weic2505 — Science Release

Webb sees galaxy is mysteriously clearing fog of early Universe

26 March 2025

Using the unique infrared sensitivity of the NASA/ESA/CSA James Webb Space Telescope, researchers can examine ancient galaxies to probe secrets of the early universe. Now, an international team of astronomers has identified bright hydrogen emission from a galaxy in an unexpectedly early time in the Universe’s history. The surprise finding is challenging researchers to explain how this light could have pierced the thick fog of neutral hydrogen that filled space at that time.

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 programmes 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. Researchers 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.

Webb discovered the incredibly distant galaxy JADES-GS-z13-1, observed to be at just 330 million years after the Big Bang, in images taken by Webb’s NIRCam (Near-Infrared Camera) as part of the JADES programme. Researchers 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, an international team led by Joris Witstok of the University of Cambridge in the United Kingdom as well as the Cosmic Dawn Center and the University of Copenhagen in Denmark, 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-α emission radiated by hydrogen atoms.[1] 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," explained Roberto Maiolino, a team member from the University of Cambridge and University College London. “Most of this haze was lifted in a process called reionisation, 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-α 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 reionisation [2], the immense amounts of neutral hydrogen fog surrounding galaxies blocked any energetic ultraviolet light they emitted, much like the filtering effect of coloured glass. Until enough stars had formed and were able to ionise the hydrogen gas, no such light — including Lyman-α emission — could escape from these fledgling galaxies to reach Earth. The confirmation of Lyman-α radiation from this galaxy, therefore, has great implications for our understanding of the early Universe. Team member Kevin Hainline of the University of Arizona in the United States, says “We really shouldn’t have found a galaxy like this, given our understanding of the way the Universe has evolved. 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 reionised.”

The source of the Lyman-α 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. Witstok elaborates: “The large bubble of ionised 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”. A powerful active galactic nucleus (AGN) [3], driven by one of the first supermassive black holes, is another possibility identified by the team.

The new results could not have been obtained without the incredible near-infrared sensitivity of Webb, necessary not only to find such distant galaxies but also to examine their spectra in fine detail. Former NIRSpec Project Scientist, Peter Jakobsen of the Cosmic Dawn Center and the University of Copenhagen in Denmark, recalls: “Following in the footsteps of the Hubble Space Telescope, it was clear Webb would be capable of finding ever more distant galaxies. As demonstrated by the case of GS-z13-1, however, it was always going to be a surprise what it might reveal about the nature of the nascent stars and black holes that are formed at the brink of cosmic time.”

The team plans further follow-up observations of GS-z13-1, aiming to obtain more information about the nature of this galaxy and origin of its strong Lyman-α radiation. Whatever the galaxy is concealing, it is certain to illuminate a new frontier in cosmology.

This new research has been published today in Nature. The data for this result were captured as part of JADES under JWST programmes #1180 (PI: D. J. Eisenstein), #1210, #1286 and #1287 (PI: N. Luetzgendorf), and the JADES Origin Field programme #3215 (PIs: Eisenstein and R. Maiolino).

Notes

[1] The name comes from the fact that a hydrogen atom emits a characteristic wavelength of light, known as “Lyman-alpha” radiation, that is produced when its electron drops from the second-lowest to the lowest orbit around the nucleus (energy level).

[2] The epoch of reionisation was a very early stage in the Universe’s history that took place after recombination (the first stage following the Big Bang). During recombination, the Universe cooled enough that electrons and protons began to combine to form neutral hydrogen atoms. Reionisation began when denser clouds of gas started to form, creating stars and eventually entire galaxies. They produced large amounts of ultraviolet photons, which gradually reionised the hydrogen gas. As neutral hydrogen gas is opaque to energetic ultraviolet light, we can only see galaxies during this epoch at longer wavelengths until they create a “bubble” of ionised gas around them, so that their ultraviolet light can escape through it and reach us.

[3] An active galactic nucleus is a region of extremely strong radiation at the centre of a galaxy. It is fuelled by an accretion disc, made of material orbiting and falling into a central supermassive black hole. The material crashes together as it spins around the black hole, heating to such extreme temperatures that it radiates highly energetic ultraviolet light and even X-rays, rivalling the brightness of the whole galaxy surrounding it.

More information

Webb is the largest, most powerful telescope ever launched into space. Under an international collaboration agreement, ESA provided the telescope’s launch service, using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the workhorse spectrograph NIRSpec and 50% of the mid-infrared instrument MIRI, which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).

Image Credit: ESA/Webb, NASA, STScI, CSA, 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)