The James Webb Telescope observes galaxies shortly after the Big Bang

The James Webb Space Telescope is once again providing stunning insights into the past. Researchers have now identified three galaxies that were actively forming 400 to 600 million years after the Big Bang. These young galaxies are surrounded by an unusually large amount of dense gas, which may have contained the universe's first elements.

Galaxies are like islands in a sea of ​​gas

“These galaxies are like shimmering islands in a sea of ​​neutral, opaque gas,” explains Kasper Heintz, lead author of the study and professor of astrophysics at the Cosmic Dawn Center at the University of Copenhagen, in a statement. press release. “If it weren’t for Webb, we wouldn’t be able to observe these very early galaxies, let alone learn much about their formation.”

The telescope's spectroscopic data show that light from these galaxies is absorbed by large amounts of neutral hydrogen gas. “The gas must be widespread and cover a very large portion of the galaxy,” said co-author Darach Watson. “This suggests that we are observing the formation of neutral hydrogen gas in galaxies. This gas will cool, clump together and form new stars.

Galaxies in the era of reionization

At the time of the observed galaxies, the so-called reionization epoch, a few hundred million years after the Big Bang, the gas between stars and galaxies was largely opaque. Only about a billion years after the Big Bang, the density of elements in the entire universe decreased due to radiation from stars and the universe became completely transparent.

“The fact that we see large reservoirs of gas also suggests that the galaxies have not had enough time to form most of their stars,” Watson continued. By comparing the new data with models of star formation, astronomers found mainly clusters of young stars.

“We are moving away from the idea that galaxies are isolated ecosystems. At this point in the history of the universe, all galaxies are closely connected to the intergalactic medium with its filaments and pristine gas structures,” adds co-author Simon Nielsen.

New insights thanks to the web

“It was impossible to obtain images and data of these distant galaxies before the Webb Telescope,” Associate Professor Gabriel Brammer emphasizes in the statement. “We also had a good idea of ​​what we would find in the data – we were essentially making discoveries at first glance.”

The study now opens up many new questions for astronomy: Where exactly is the gas? How much is there in the centers or edges of galaxies? Is it pure gas or enriched with heavier elements? “The next step is to create large statistical samples of galaxies and measure in detail the prevalence and importance of their features,” says study leader Heintz. The researchers published their results in the specialized journal Sciences.

Image source: NASA, ESA, Canadian Space Agency, Joseph Olmstead (STScI)