Surprising galaxy shines through fog of the early universe
- The early universe was filled with a thick fog of neutral hydrogen. Even though the first stars and galaxies emitted copious amounts of ultraviolet light, that light struggled to pierce the fog.
- It took hundreds of millions of years for the neutral hydrogen to become ionized – electrons stripped from protons – allowing light to travel freely through space.
- But one galaxy with a bright, unexpected hydrogen emission caught astronomers by surprise. We see the galaxy JADES-GS-z13-1 just 330 million years after the Big Bang. It has a strong hydrogen emission line even though the cosmic fog should have absorbed it.
NASA published this original story on March 26, 2025. Edits by EarthSky.
Surprising galaxy in the early universe
Using NASA’s James Webb Space Telescope, researchers can examine ancient galaxies to probe secrets of the early universe. On March 26, 2025, an international team of astronomers said they’ve identified bright hydrogen emission from a galaxy in an unexpectedly early time in the universe’s history. The surprise finding challenges researchers to explain how this light could have pierced the thick fog of neutral hydrogen that filled space at that time.
Joris Witstok of the University of Cambridge in the United Kingdom and the Cosmic Dawn Center at the University of Copenhagen in Denmark led the international team. The researchers published their peer-reviewed study in the journal Nature on March 26, 2025.
The discovery of the surprising galaxy
The Webb telescope’s Near-Infrared Camera (NIRCam) discovered the incredibly distant galaxy JADES-GS-z13-1. We observe it as it existed just 330 million years after the Big Bang. Researchers used the galaxy’s brightness in different infrared filters to estimate its redshift. A redshift measures a galaxy’s distance from Earth based on how its light has 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 researchers then observed the galaxy using Webb’s Near-Infrared Spectrograph (NIRSpec) instrument.
In the resulting spectrum, the scientists confirmed the redshift as 13.0. So this equates to seeing the galaxy just 330 million years after the Big Bang. That would be just 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, known as 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.
Seeing through the fog
Roberto Maiolino, a team member from the University of Cambridge and University College London, explained:
The early universe was bathed in a thick fog of neutral hydrogen. Most of this haze was lifted in a process called reionization, which was completed about 1 billion years after the big bang. We see GS-z13-1 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 era of reionization, there were immense amounts of neutral hydrogen fog. It surrounded galaxies, blocking any energetic ultraviolet light they emitted. Picture it similar to the filtering effect of colored glass. Until enough stars formed and could 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.
Kevin Hainline, a team member from the University of Arizona, said:
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 reionized.
Looking for answers
Scientists don’t yet know the source of the Lyman-alpha radiation from this galaxy. But it may include the first light from the earliest generation of stars to form in the universe. Witstok said:
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.
A powerful active galactic nucleus, driven by one of the first supermassive black holes, is another possibility the team identified.
Bottom line: Astronomers have discovered a surprising galaxy showing a bright hydrogen emission shining through the fog of the early universe.
Source: Witnessing the onset of reionization through Lyman-a emission at redshift 13
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