JWST recently caught three of the earliest galaxies in the universe as they were contracting from a giant, dark cloud of hydrogen gas.
The three faint spots of red light in a recent set of JWST data traveled more than 13 billion light-years through space to reach the telescope’s mirrors. That ancient light provides a snapshot of what galaxies looked like between 400 and 600 million years after the Big Bang, when the universe was still a cosmic toddler. And all three of these early galaxies are shrouded in dense hydrogen gas, which slowly falls into the galaxies’ gravity wells – where it will eventually help them form new stars.
Astrophysicist Kasper Heintz of the University of Copenhagen and his colleagues published their work in the journal Science.
This artist’s illustration shows a young galaxy, just a few hundred million years after the Big Bang, still trying to pull itself out of the surrounding cold hydrogen gas.
NASA, ESA, CSA, Joseph Olmsted (STScI)
The era of reionization will begin Illuminated
JWST’s instruments usefully split the light from distant galaxies into its constituent wavelengths. The spectrum of light emanating 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 own very specific wavelengths of light. Around the three distant galaxies, Heintz and his colleagues noticed that something seemed to absorb the same wavelengths of light as cold hydrogen gas – and a lot of of it.
“These galaxies are like sparkling islands in a sea of otherwise neutral, opaque gas,” Heintz said in a recent statement.
When it is cold and not electrically charged (or ionized), hydrogen gas 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 remove electrons from all those hydrogen atoms, creating ionized gas (also called plasma) that is translucent instead of opaque. The age of reionization had begun – and the three galaxies in Heintz and his colleagues’ recent study are only now beginning to make this clear.
Brand new galaxies, some assembly required
Sometime between 13.2 billion and 13.4 billion years ago—when the light that just reached JWST began its long journey through space—these three early galaxies were still assembling themselves from the surrounding gas.
“[The data] suggests that we are seeing the assembly of neutral hydrogen in galaxies,” astrophysicist Darach Watson of the University of Copenhagen, co-author of the recent study, said in a statement. And that’s a stage in galaxy formation that astronomers haven’t seen before, especially in the very early universe.
The galaxies are still in their infancy and are still surrounded by a cloud of cold, dark, neutral hydrogen gas – the same stuff that caused the cosmic Dark Ages. Most of that gas will be heated as it falls into the galaxies, drawn in by their inexorable gravity. And then it will slowly cool and form clumps like solidified oatmeal, and some of those clumps will be so heavy that they collapse on themselves and form new stars.
At this time (or as we see them now, what happened billions of years ago), the stars containing these early galaxies are mostly young and newly formed.
“The fact that we see large reservoirs of gas also suggests that galaxies have not yet had enough time to form most of their stars.” But they will probably get there.
The data not only reveals a previously unseen moment in a galaxy’s life, but also a glimpse of what the early universe looked like before the expansion of space pulled everything further apart, turning most galaxies into lonely beacons, or on are best isolated clusters of light. in the void.
“We are moving away from the view of galaxies as isolated ecosystems,” said astrophysicist Simone Nielsen of the University of Copenhagen in a recent statement. “At this stage in the history of the universe, galaxies are all intimately connected to the intergalactic medium with its filaments and structures of pristine gas.”
In the very early universe, no galaxy was (yet) an island.