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, 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. Joris 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) [2], 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).