How galaxies grew in the early Universe

JWST recently captured three of the universe’s earliest galaxies being pulled together by a giant, dark cloud of hydrogen gas.

The three faint specks of red light in a recent JWST data set traveled more than 13 billion light-years through space to reach the telescope’s mirrors. That ancient light carries a snapshot of what galaxies looked like between 400 and 600 million years after the Big Bang, when the universe was essentially a cosmic baby. And all three of these early galaxies are covered in dense hydrogen gas, which is slowly falling into the galaxies’ gravity wells — where it will eventually help them form new stars.

University of Copenhagen astrophysicist Kasper Heintz and his colleagues published their work in the journal science.

The age of reionization will be Turned on

JWST’s instruments 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 own very specific wavelengths of light. Around three distant galaxies, Heintz and his colleagues noticed that something appeared to be absorbing the same wavelengths of light as cold hydrogen gas—and LOT hers.

“These galaxies are like gaseous islands in a sea of ​​otherwise neutral, dark gas,” Heintz says 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 several 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 ionizing gas (also called plasma) that is transparent instead of dark. The age of reionization had begun – and the three galaxies in Heintz and his colleagues’ latest study are just beginning to illuminate it.

Brand New Galaxies, Little Assembly Required

Somewhere between 13.2 billion and 13.4 billion years ago—when the light just reaching JWST began its long journey through space—these three early galaxies were still in the process of being assembled from the surrounding gas.

“[The data] suggests that we are seeing the accretion of neutral hydrogen in galaxies,” University of Copenhagen astrophysicist Darach Watson, a co-author of the latest study, said in a statement. And it’s a phase 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 stuff that caused the cosmic dark ages. Much of that gas will heat up as it falls into galaxies, pulled by their relentless gravity. And then it will slowly cool, forming lumps like clotted oats, 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 are seeing large reservoirs of gas also suggests that the galaxies have not yet had enough time to form most of their stars.” But they will get there, most likely.

The data reveal not only a never-before-seen moment in a galaxy’s life, but also a glimpse of what the early universe was like before the expansion of space pulled everything away, turning most galaxies into beacons. solitary, or at most isolated clusters of lights. in the void.

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

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