NASA’s James Webb Space Telescope has come up with the goods again. Images released by the space agency show some of the oldest ever discovered barred galaxies. The galaxies feature so-called stellar bars – elongated bands of stars that stretch from the galaxies’ centres into their outer disks like those seen in the Milky Way. Two of the six date back to a time when the Universe was just 3.4 billion years old, one quarter of its current age.
One of the galaxies, EGS-23305, was previously imaged by the Hubble Space Telescope but the resolution was not high enough for astronomers to make out its spiral shape and prominent stellar bar. These fine details are clearly visible in the higher resolution image produced by Webb. The structure of a second galaxy, EGS-24268, is also clearly visible.
Both barred galaxies date back to around 11 billion years ago, making them older than any previously discovered, and were found in data collected by Webb’s Cosmic Evolution Early Release Science Survey (CEERS).
Four other barred galaxies from more than 8 billion years ago were also found in the data.
“I took one look at these data, and I said, ‘We are dropping everything else!’” said the study's co-author Prof Shardha Jogee, of The University of Texas at Austin.
“The bars hardly visible in Hubble data just popped out in the JWST image, showing the tremendous power of JWST to see the underlying structure in galaxies.”
Stellar bars play a central role in the evolution of galaxies by transporting gas from the outer regions to the centre. This gas is then rapidly converted into new stars at a rate between 10 and 100 times faster than in the rest of the galaxy. It can also help to fuel the growth of the supermassive black holes found at galaxies' centres.
Finding barred galaxies so early in the Universe also raises questions about current theories of galaxy evolution. The team now plan to test different models of galactic evolution to explain their new findings.
“This discovery of early bars means galaxy evolution models now have a new pathway via bars to accelerate the production of new stars at early epochs,” said Jogee.
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