James Webb spots early galaxies feeding on cold gas

24 May 2024

Artist's illustration of a galaxy forming only a few hundred million years after the big bang. Image: NASA/ESA/CSA/Joseph Olmsted (STScI)

The data collected on these early forming galaxies could help scientists learn more about how the universe developed in the first billion years after the big bang.

Researchers looking at data from the James Webb Space Telescope have gained new insights on galaxies forming during an earlier period of the universe.

These three galaxies are believed to be actively forming when the universe was only 400m to 600m years old – compared to the universe’s current estimated age of roughly 13.7bn years. Thanks to Webb’s powerful instruments, researchers can peer into this early period and learn more about how the universe was formed.

Webb’s data on this early period shows these three galaxies are surrounded by gases. The researchers suspect these gases are almost purely hydrogen and helium, the earliest elements to exist in the cosmos.

The unusual amount of gas surrounding these galaxies means the team suspects these gases will fuel the formation of new stars in these galaxies. Simone Nielsen, a PhD student and co-author of the study, explains how different the universe looked during this earlier period.

“We’re moving away from a picture of galaxies as isolated ecosystems,” Nielsen said. “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.”

This earlier period is known as the Era of Reionisation, when gases between stars and galaxies were largely opaque. The change to transparency didn’t occur until roughly 1bn years after the big bang. The new data could help researchers learn more about how this transition occurred.

By combining spectra with Webb images, the team found that the light from these three forming galaxies is being absorbed by large amounts of neutral hydrogen gas.

“The gas must be very widespread and cover a very large fraction of the galaxy,” said study co-author and associate professor Darach Watson. “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.”

By matching James Webb’s data to existing models of star formation, the researchers also found that these galaxies primarily have populations of young stars, suggesting these galaxies have not had enough time to form most of their stars yet.

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Leigh Mc Gowran is a journalist with Silicon Republic