A galaxy spotted just 330 million years after the Big Bang has been implicated in bringing light to the choking dark of the early Universe.
It’s called JADES-GS-z13-1, and an analysis of the very faint light it has sent from more than 13.4 billion years ago reveals that it played a role in the Epoch of Reionization – the billion-year process that cleared the opaque fog that filled the early Universe, allowing light to stream freely.
This epoch of the Universe’s history is really hard to see, making the mechanisms behind it something of a mystery. JADES-GS-z13-1 literally sheds light into an age of cosmic darkness. The result is a signature emission called Lyman-alpha which is emitted by hydrogen as it changes energy states and can only be seen once reionization has taken place.
“The early Universe was bathed in a thick fog of neutral hydrogen,” says astrophysicist Roberto Maiolino of the University of Cambridge and University College London in the UK.
“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.”
Here’s how the story goes. At the beginning of the Universe as we know it, within minutes of the Big Bang, space was filled with a hot, dense fog of plasma consisting of small atomic nuclei and free electrons. What little light there was wouldn’t have penetrated this fog; photons would simply have scattered off the electrons floating around, effectively making the Universe dark.
After about 300,000 years, as the Universe cooled, protons and electrons began to come together to form neutral hydrogen (and a little bit of helium) gas. Most wavelengths of light could penetrate this neutral medium, but there was little in the way of light to produce it.
But from this hydrogen and helium, the first stars and galaxies were born.
Those first light sources delivered powerful radiation that knocked electrons off the neutral hydrogen, returning it to an ionized state once more. By this point, however, the Universe had expanded so much that the gas was exponentially more diffuse, allowing light to pass through more easily and begin its long journey across the stretches of time and space.
By about 1 billion years after the Big Bang, following the period known as the Cosmic Dawn, the Universe was transparent, the way we see it today. Et voilà! The lights were on.
The problem with JADES-GS-z13-1 is that, even if it’s participating in reionization, we still shouldn’t be able to see it. The space immediately around the galaxy would be ionized, creating a bubble of clarity about 650,000 light-years across at the time we see it; but fog should still be wrapped around this little cavity of brilliance the galaxy has carved in space-time.
“We really shouldn’t have found a galaxy like this, given our understanding of the way the Universe has evolved,” says astronomer Kevin Hainline of the University of Arizona in the US.
“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.”
A closeup of JADES-GS-z13-1. (ESA/Webb, NASA, STScI, CSA, JADES Collaboration, Brant Robertson, Ben Johnson, Sandro Tacchella, Phill Cargile, J. Witstok, P. Jakobsen, A. Pagan, M. Zamani)
We thought we had a pretty good handle on the timeline and process of reionization. JADES-GS-z13-1 throws that for a loop. One possible explanation is that a rapidly feeding black hole is responsible, causing material around it to heat up and blaze with light.
Another explanation for the Lyman-alpha brightness could be a large number of really massive, hot stars, between 100 and 300 times the mass of the Sun.
Both prospects are intriguing, since each offers a different window into the infancy of the Universe; but, at this point, neither can be confirmed.
Future observations of the strange galaxy are planned to help astronomers learn more. One thing that is becoming clear, like the space around JADES-GS-z13-1: the more we learn about the early Universe, the more confusing it gets.
“Following in the footsteps of the Hubble Space Telescope, it was clear Webb would be capable of finding ever more distant galaxies,” explains astronomer Peter Jakobsen of the University of Copenhagen in Denmark.
“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 research has been published in Nature.
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