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JWST recently captured three of the earliest galaxies in the universe being accreted by a giant dark cloud of hydrogen gas.

The three dark patches of red light in a recent batch of JWST data traveled more than 13 billion light-years through space to reach the telescope’s mirrors. This ancient light brings a snapshot of what galaxies looked like between 400 and 600 million years after the Big Bang, when the universe was basically a cosmic infant. All three of these early galaxies are enveloped in dense hydrogen gas, which slowly falls into the galaxies’ gravitational wells — where it will eventually help them form new stars.

University of Copenhagen astrophysicist Kasper Heinz and colleagues published their work in the journal Science.

The Age of Reionization will be Lit

JWST’s instruments helpfully separate the light from distant galaxies into the individual wavelengths that make it up. The spectrum of light coming from an object such as a galaxy is like a fingerprint of the chemicals that make it up, because each chemical compound absorbs, emits, and reflects its very specific wavelengths of light. Around the three distant galaxies, Heinz and his colleagues noticed that something seemed to absorb the same wavelengths of light as cold hydrogen gas—and a lot from him.

“These galaxies are like sparkling islands in a sea of ​​otherwise neutral, opaque gas,” Heinz said in a recent statement.

Hydrogen gas, when cold and not electrically charged (or ionized), absorbs light but does not emit it. This neutral gas filled the early universe, making it impossible for light to travel very far, until a few hundred million years after the Big Bang: a period called the cosmic dark ages.

It took powerful bursts of radiation from the first stars in the first galaxies to strip electrons from all those hydrogen atoms, creating an ionized gas (also called plasma) that was translucent instead of opaque. The age of reionization has begun—and all three galaxies in the recent study by Heinz and colleagues are just beginning to light it up.

Brand new galaxies, assembly required

Sometime between 13.2 billion and 13.4 billion years ago—when the light that had just reached JWST began its long journey through space—these three early galaxies were still being assembled from the surrounding gas.

“[The data] suggests that we are seeing the assembly of neutral hydrogen into galaxies,” University of Copenhagen astrophysicist Darrah Watson, co-author of the recent study, said in a statement. And it’s a stage of galaxy formation that astronomers haven’t seen before, especially in the very early universe.

Galaxies, in their infancy, are still surrounded by a cloud of cold, dark, neutral hydrogen gas—the same thing that caused the cosmic dark ages. Most of this gas will heat up as it falls into the galaxies, drawn by their relentless gravity. And then it will slowly cool, forming lumps like hardened oatmeal, and some of those lumps will be so heavy that they will collapse in on themselves to form new stars.

Right now (or as we see them now, which actually happened billions of years ago), the stars that contain these early galaxies are mostly young and newly formed.

“The fact that we see large reservoirs of gas also suggests that the galaxies haven’t had enough time to form most of their stars yet.” But they will most likely get there.

The data reveal not only a never-before-seen moment in the life of a galaxy, but also a glimpse of what the early universe was like before the expansion of space pushed everything apart, turning most galaxies into lone beacons, or at most isolated clumps of light, in the void .

“We are moving away from the picture of galaxies as isolated ecosystems,” University of Copenhagen astrophysicist Simon Nielsen said in a recent statement. “At this stage in the history of the universe, all galaxies are tightly bound to the intergalactic medium with its filaments and structures of pure gas.”

In the very early universe, no galaxy was an island (yet).