Earliest known galaxies date back 13.4 billion years

Using data collected by the James Webb Space Telescope (JWST), an international team of astronomers has recently discovered the earliest and most distant galaxies confirmed to date. The telescope captured light emitted by these galaxies over 13.4 billion years ago, suggesting that the galaxies date back to less than 400 million years after the Big Bang, a period when the universe was only two percent of its current age.

Through initial observations from JWST, scientists discovered several candidate galaxies at extreme distances, as had earlier observations from the Hubble Space Telescope. Now, four of these galaxies have been confirmed through long spectroscopic observations, which provide reliable measurements of their distances, as well as details about their physical properties.

“We’ve discovered galaxies at fantastically early times in the distant universe,” said Brant Robertson, a professor of Astronomy and Astrophysics at the University of California, Santa Cruz. “With JWST, for the first time we can now find such distant galaxies and then confirm spectroscopically that they really are that far away.” 

Scientists usually measure the distance to a galaxy by determining its so-called “redshift.” Due to the expansion of the universe, distant astronomical objects such as stars appear to be receding from us, and their light is stretched to longer, redder wavelengths by the Doppler effect. While photometric methods based on images captured through various filters can provide redshift estimates, definitive measures require spectroscopy, a technique that separates the light from an object into its component wavelengths.

The new JWST observations discovered four galaxies with redshifts higher than 10. While two galaxies initially observed by Hubble now have confirmed redshifts of 10.38 and 11.58, the other two galaxies detected by JWST have redshifts of 13.20 and 12.63, making them the most distant galaxies confirmed by spectroscopy to date, with a redshift of 13.20 corresponding to approximately 13.5 billion years ago.

“These are well beyond what we could have imagined finding before JWST. At redshift 13, the universe is only about 325 million years old,” Robertson explained. According to the researchers, star formation in these early galaxies most likely began about 100 million years earlier than the age at which they were observed, pushing the formation of the earliest stars back to approximately 225 million years after the Big Bang.

“It is hard to understand galaxies without understanding the initial periods of their development. Much as with humans, so much of what happens later depends on the impact of these early generations of stars. So many questions about galaxies have been waiting for the transformative opportunity of Webb, and we’re thrilled to be able to play a part in revealing this story,” concluded co-author Sandro Tacchella, an astrophysicist at the University of Cambridge.

These new findings are described in two papers that can be found here and here.

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By Andrei Ionescu, Earth.com Staff Writer

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