At a time when light couldn’t easily travel through space due to a thick fog of neutral hydrogen, one galaxy managed to carve out its own bubble of clear space, allowing us to detect a specific light signal that should have been completely absorbed. This cosmic lighthouse from 13 billion years ago gives us our earliest direct glimpse of how the universe transitioned from darkness to light.
The galaxy, cataloged as JADES-GS-z13-1-LA, was observed at what scientists call a redshift of 13. While that technical term might not mean much to most of us, it represents an incredible distance in both space and time. When we look at this galaxy, we see light that has traveled for over 13 billion years to reach us.
This study, published in Nature, used the James Webb Telescope to observe this early galaxy. Scientists also detected a Lyman-alpha emission, a specific wavelength of light that’s easily absorbed by neutral hydrogen, the gas that filled the early universe. Finding this emission suggests this galaxy was actively clearing the cosmic fog around it, like turning on a light in a dark room.
From Cosmic Dark Ages to First Light
Recent observations with the James Webb Space Telescope have already revealed surprisingly bright galaxies existed earlier than astronomers expected. But this new finding provides something more concrete: direct evidence of reionization, the cosmic transformation that brought the universe out of darkness.
For context, in the first few hundred thousand years after the Big Bang, the universe expanded and cooled enough for protons and electrons to combine into neutral hydrogen atoms. This created a cosmic fog that blocked most light from traveling freely for hundreds of millions of years, a period astronomers call the cosmic “dark ages.”
Eventually, the first stars and galaxies began forming and producing ultraviolet radiation that started breaking apart these neutral hydrogen atoms. This gradually made the universe transparent to light (reionization).
Breaking Through the Cosmic Fog
The research team analyzed this distant galaxy using imaging and spectroscopy from JWST’s powerful instruments. The data revealed not just the usual signs of light being blocked by early-universe hydrogen, but also a surprisingly bright signal of light breaking through. Such strong emissions had previously only been seen in much younger galaxies when more of the universe had already been cleared of neutral hydrogen.
Astronomers also saw what they call an “extremely blue ultraviolet continuum” (essentially meaning this galaxy appears very blue in color). The fact that we could even see the Lyman-alpha emission means the galaxy was incredibly good at making and releasing powerful radiation, strong enough to break apart the hydrogen gas around it.
“We know from our theories and computer simulations, as well as from observations at later epochs, that the most energetic UV light from the galaxies ‘fries’ the surrounding neutral gas, creating bubbles of ionized, transparent gas around them,” says study author Joris Witstok from the University of Copenhagen, in a statement. “These bubbles percolate the Universe, and after around a billion years, they eventually overlap, completing the epoch of reionization. We believe that we have discovered one of the first such bubbles.”
What could produce such powerful radiation in this ancient galaxy? One explanation involves extremely massive, hot stars that are much more efficient at producing ionizing radiation than typical stars today. These cosmic giants could be heating surrounding gas to temperatures exceeding 100,000 Kelvin, far hotter than our Sun’s surface at about 5,800 Kelvin.
Another possibility is that this galaxy contains an active supermassive black hole. The intense radiation from material falling into such a black hole could efficiently ionize nearby gas. Supporting this idea, the researchers found the galaxy appears extremely compact, smaller than 114 light-years across which is more compact than most galaxies seen at similar distances.
“Most galaxies are known to host a central, supermassive black hole. As these monsters engulf surrounding gas, the gas is heated to millions of degrees, making it shine brightly in X-rays and UV before disappearing forever,” says Witstok.
The researchers also considered whether this might be one of the universe’s very first generation of stars, called Population III stars, formed from pristine gas containing only hydrogen and helium. These stars would be substantially more massive and hotter than later stars. However, the galaxy seems slightly too bright to fit this explanation perfectly.
Rewriting the Timeline of Cosmic Dawn
Whatever is powering this ancient light source, its discovery reshapes our understanding of how the universe transitioned from darkness to light. Until recently, the consensus among astronomers was that reionization did not begin until the Universe was around half a billion years old, completing another half billion years later. But this study pushes the beginning of reionization significantly earlier than previously thought.
The finding also provides evidence for an important physical process called Wouthuysen-Field coupling, where Lyman-alpha photons affect the spin temperature of hydrogen atoms. Scientists hope to detect this with radio telescopes searching for signals from the early universe.
“We knew that we would find some of the most distant galaxies when we built Webb,” says study author Peter Jakobsen from the University of Copenhagen. “But we could only dream of one day being able to probe them in such detail that we can now see directly how they affect the whole Universe.”
The universe’s first light didn’t switch on all at once; it started with galaxies like this one, each creating its own bubble of clear space that eventually merged with others to transform the entire cosmos. By pushing back the timeline of this process and showing it began with ordinary galaxies rather than exceptional ones, this discovery connects the dots between the universe’s first few hundred million years and the transparent cosmos that would eventually allow for our existence.
Source : https://studyfinds.org/webb-telescope-universe-turning-on-its-lights/