NASA Early Galaxy Discovery Shines Light on 'Cosmic Dark Ages'

A new discovery by NASA's flagship James Webb Space Telescope has pushed forward the confirmed end date of the so-called "Cosmic Dark Ages" by some 270 million years.

In their study, an international team of researchers led by astrophysicist Joris Witstok of the University of Cambridge in England, analyzed the distant galaxy JADES-GS-z13-1-LA.

It is so far away that the light from it takes some 13.4 billion years to reach us, meaning we see it as it was just 330 million years after the big bang.

And from JADES-GS-z13-1-LA the team detected a signal of "reionization," the process through which the first stars made the universe once again transparent to light.

"We report the discovery of one of the most distant galaxies known to date," Witstok told Newsweek. "Unlike any other similarly distant galaxy, it shows a very clear, telltale signature that implies the galaxy contains a remarkably powerful source of extreme ultraviolet radiation.

"This also suggests it has made an unexpectedly early start to cosmic reionization, the process where neutral gas in between early galaxies is heated into a plasma by energetic radiation from stars and black holes forming in the first galaxies."

What Is Reionization?

In the wake of the big bang, the universe gradually cooled down from its original, ultra-hot state, eventually allowing—around the universe's 380,000th birthday—free protons and electrons to combine into a fog mainly made up of neutral hydrogen atoms.

Because of this, even when the first stars formed, some 13.7 billion years ago, their light was quickly extinguished by the gas cloud. It is because of this (and the few other sources of light at the time) that this period is called the Cosmic Dark Ages.

Over time, sufficiently energetic ultraviolet radiation from the first stars and galaxies increasingly split the neutral hydrogen atoms back into electrons and protons—that is, "reionizing" them.

"The emergence of these first stars marks the end of the "Dark Ages" in cosmic history, a period characterized by the absence of discrete sources of light," NASA explains on its website.

"Understanding these first sources is critical, since they greatly influenced the formation of later objects such as galaxies. The first sources of light act as seeds for the later formation of larger objects."

Those wavelengths of ultraviolet light that are absorbed by neutral hydrogen atoms are known to physicists as the "Lyman continuum." Only once the hydrogen gas had been made transparent to Lyman photos by higher-energy, shorter-wavelength radiation could such light shine out into the wider universe (and, in some cases, reach Earth for us to see.)

In their study, Witstok and his colleagues report detecting a signal of reionization coming from JADES-GS-z13-1-LA from 330 million years ago.

This bright emission has been identified as "Lyman-α," a signal associated with neutral hydrogen transitioning back down from an excited to a ground state.

Its detection means that, firstly, JADES-GS-z13-1-LA produced enough high-energy radiation to excite its neutral hydrogen, and secondly that there was little neutral hydrogen between the galaxy and Earth to block the Lyman-α photons from reaching us in the present.

"Up to this point, a similarly strong Lyman-α signal has not been observed until more than 600 million years after the Big Bang, whereas this galaxy is seen when the Universe was almost twice as young," Witstok said.

The source of the ionizing emissions, the researchers said, is most likely either massive, hot stars (the earliest stars were likely 30–300 times more massive than our sun and millions of times more bright) or a supermassive black hole.

In an associated comment paper, University of Melbourne physicist Professor Michele Trenti —who was not involved in the present study— said that the signal's detection "implies that a bubble of ionized gas surrounded the radiation source, preventing the short-wavelength light being absorbed shortly after emission.

"The authors estimate that this bubble must have had a radius of at least 200,000 parsecs (650,000 light years)," Trenti said. "This represents the minimum distance required for the photons to travel and stretch to redder wavelengths sufficiently for them to continue their journey unimpeded through neutral hydrogen gas."

With their initial study complete, the researchers are continuing to study JADES-GS-z13-1-LA in more detail—with observations of the far-flung galaxy still ongoing.

At the same time, Witstok explained, the team is also looking for other examples of very early galaxies with a bright Lyman-α signal.

He said: "This will shed light on the precise moment reionization started, and whether it is very massive, hot stars or a black hole at the center of the galaxy responsible for the extraordinarily powerful ultraviolet radiation."

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Reference

Witstok, J., Jakobsen, P., Maiolino, R., Helton, J. M., Johnson, B. D., Robertson, B. E., Tacchella, S., Cameron, A. J., Smit, R., Bunker, A. J., Saxena, A., Sun, F., Alberts, S., Arribas, S., Baker, W. M., Bhatawdekar, R., Boyett, K., Cargile, P. A., Carniani, S., Charlot, S., ... Zhu, Y. (2025). Witnessing the onset of reionization through Lyman-α emission at redshift 13. Nature. https://doi.org/10.1038/s41586-025-08779-5