It all started with the simplest element in the universe. Just a few hundred thousand years after the Big Bang, the cosmos had cooled enough for protons and electrons to stop traveling separately and come together to form hydrogen atoms, the simplest element in the universe: one proton and one electron.
As hydrogen filled space, it began to behave like an immense cosmic fog. It absorbed the most energetic light emitted by the first stars and galaxies, hiding them behind an almost impenetrable curtain. For hundreds of millions of years, the universe was a place full of luminous objects… that could barely be seen. It was the Dark Ages of the cosmos. How did the universe get out of that darkness?
The answer was a process known as cosmic reionization, a transformation that forever changed history. The first generations of stars began to emit enormous amounts of ultraviolet radiation. Little by little, That light was once again tearing the electrons from the hydrogen atoms, converting the neutral gas into plasma and making the universe transparent again. It was as if someone had lifted the curtain on the universe. While it is true that reionization did not create the first galaxies, it allowed them to be seen for the first time.
But even today scientists debate which objects produced enough radiation to achieve such a transformation, who were responsible for “raising that curtain.” The radiation responsible for this process belongs to what It is known as the Lyman continuum and is still very difficult to detect today. Not only because distant galaxies are very faint, but because much of that light disappears before reaching Earth.
That is why astronomers often turn to relatively nearby galaxies to try to understand how reionization could have occurred more than 13 billion years ago. And that is the object of a new study published in The Astrophysical Journal. The authors, led by Ilias Goovaerts of the Space Telescope Science Institute, discovered that the Hubble space telescope detected precisely that type of radiation from a galaxy (known as JADES-GS-z13-1-LA) located about 11,000 million light years away. The analyzes indicate that a surprisingly high fraction of its ultraviolet radiation manages to escape into space: up to 65%, much higher than expected for this type of galaxy.
That means that almost two out of every three photons capable of ionizing hydrogen leave the galaxy without being absorbed by its own gas. It is precisely this type of “leaks” that would have allowed the first galaxies to completely transform the early Universe. Goovaerts’ team believes that the intense star formation activity of this galaxy may have something to do with it. Massive stars produce enormous amounts of ultraviolet radiation and, when they subsequently explode as supernovae, they can open “windows” through which the radiation can escape into space. The result would be a galaxy much more transparent than usual.
While the finding alone does not solve the mystery of reionization, it does provide direct evidence that some galaxies in the early Universe were capable of releasing enormous amounts of ionizing radiation. If many of them behaved in a similar way, They could explain how the cosmos went from being a place full of neutral hydrogen to becoming the infinite transparent sky that we observe today.
But perhaps the most fascinating thing is not the galaxy, but the light itself. Each of those photons left their galaxy when the Earth didn’t even exist. For about 11,000 million years, it crossed regions full of gas capable of absorbing it and, even so, it managed to reach the Hubble mirror. For a photon in the Lyman continuum, that journey is almost a feat. And precisely because almost none of them succeed, each one that reaches us contains extraordinarily valuable information. Each photon in the Lyman continuum allows us to deduce what the galaxy that emitted it was like.what paths he found to escape and even the state of the Universe he went through for billions of years. You just have to know what to ask him.