NASA's James Webb Space Telescope has spotted some of the universe's youngest galaxies forming.
These three galaxies are thought to have been taking shape when the universe was only between 400 and 600 million years old, according to a new paper in the journal Science.
The universe is thought to be about 13.8 billion years old, meaning that these young galaxies formed shortly after the Big Bang on a cosmic time scale. This marks the first time that we have observed a galaxy in the process of being born.
According to the paper, these early galaxies are surrounded almost exclusively by hydrogen and helium, which were the first elements to form at the very beginning of the universe. This gas is expected to have sparked the formation of new stars in these ancient galaxies.
"These galaxies are like sparkling islands in a sea of otherwise neutral, opaque gas," study co-author Kasper Heintz, an assistant professor of astrophysics at the Cosmic Dawn Center (DAWN) at the University of Copenhagen in Denmark, said in a statement. "Without Webb, we would not be able to observe these very early galaxies, let alone learn so much about their formation."
The universe is thought to have been born in a process known as the Big Bang, which suggests that all of space and time started from an extremely small and dense single point. About 13.8 billion years ago, this point started expanding rapidly, stretching space itself. As it expanded, it cooled down, allowing particles like protons and neutrons to form, and after about 380,000 years, the universe cooled enough for these particles to combine into atoms, mostly hydrogen and helium.
For a few hundred million years, the universe was dark as no stars had formed yet, but eventually, gravity pulled gas together to form the first stars and galaxies.
"During the few hundred million years after the Big Bang, the first stars formed, before stars and gas began to coalesce into galaxies. This is the process that we see the beginning of in our observations," study co-author Darach Watson, an associate professor at the University of Copenhagen, said in another statement.
The oldest known galaxies in the universe are thought to have formed between 300 and 400 million years after the Big Bang, which is how old astronomers think these three galaxies are.
"You could say that these are the first 'direct' images of galaxy formation that we've ever seen. Whereas the James Webb has previously shown us early galaxies at later stages of evolution, here we witness their very birth, and thus, the construction of the first star systems in the universe," Heintz said.
The researchers were able to spot these galaxies due to the large amount of hydrogen gas visible in the spectrum of light they gave off, detected thanks to James Webb Space Telescope's incredibly sensitive infrared camera. This means that the light from the young stars in these galaxies was being absorbed by vast amounts of invisible hydrogen.
"The gas must be very widespread and cover a very large fraction of the galaxy. This suggests that we are seeing the assembly of neutral hydrogen gas into galaxies. That gas will go on to cool, clump, and form new stars," Watson said. "The fact that we are seeing large gas reservoirs also suggests that the galaxies have not had enough time to form most of their stars yet."
This also marks the most distant measurement of neutral hydrogen gas, which is an essential building block for stars.
The researchers hope to further investigate the youngest galaxies in our universe and elucidate the earliest days of the cosmos.
"One of the most fundamental questions that we humans have always asked is: 'Where do we come from?' Here, we piece together a bit more of the answer by shedding light on the moment that some of the universe's first structures were created. It is a process that we'll investigate further, until hopefully, we are able to fit even more pieces of the puzzle together," co-author Gabriel Brammer, an associate professor at the University of Copenhagen, said in the statement.
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