For the first time this week, photographs from the James Webb Space Telescope (JWST) revealed that stellar bars were present in some galaxies 11 billion years ago. Stellar bars are a defining feature of about two-thirds of all spiral galaxies in the Universe, including our own Milky Way. The discovery has implications for astronomers’ understanding of galactic evolution, indicating that bars form very quickly and can persist for much of a galaxy’s lifetime, influencing its shape and structure.
Bars are regions of intense star formation that radiate from the core of a galaxy. Through the motion of inner-orbiting stars, dust, and gas clouds, they build up as a self-perpetuating wave of dense material that slowly spreads outward as it drags raw material inward. These regions become stellar nurseries that produce new stars at a rapid rate.
Six barred galaxies as seen by JSWT, as they would have appeared in the early universe, 8.4 billion to 11 billion years (Gyr) ago. Credit: NASA/CEERS/University of Texas at Austin.
The new JWST images, presented by the University of Texas at Austin on January 5, show six barred spiral galaxies more than 8.4 million years old, two of which are more than 11 billion years old (the galaxy oldest ever seen is about 13.4 billion years old). .
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Most of these galaxies were previously imaged by the Hubble Space Telescope, such as EGS-23205, shown below. (EGS stands for Extended Growth Strip, a region of the sky that has been extensively imaged and studied by international surveys). However, in the Hubble images, the bars are largely obscured.
Galaxy EGS23205 as seen by Hubble (left, taken in the near-infrared filter) and JWST (mid-infrared image right). Credit: NASA/CEERS/University of Texas at Austin.
JWST has an advantage over JWST in observing extremely old and distant galaxies, in part because its larger mirror can collect more light from distant and faint objects. But it also has an advantage because of its use of infrared rather than optical wavelengths. Light from older, more distant objects is “redshifted” along the electromagnetic spectrum, meaning JWST’s detectors can pick them up better than Hubble.
Infrared is also very effective at seeing through gas and dust, allowing JWST to pick out stellar nurseries in bars that would otherwise be obscured.
Shardha Jogee, professor of astronomy at the University of Texas at Austin, explained the implications of these early formation bars for models of galactic evolution:
The location of the Extended Growth Strip (EGS) in the night sky. Galaxies recently observed by JWST are located within the EGS. Image credit: NASA, ESA, M. Davis (University of California, Berkeley), S. Faber (University of California, Santa Cruz), and A. Koekemoer (STScI).
“Bars solve the supply chain problem in galaxies,” says Joeee. “Just as we have to carry raw material from the harbor to the factories in the interior that make new products, a bar carries strong gas into the central region where the gas rapidly turns into new stars at a rate typically of 10 to 100 times faster than in the central region rest of the galaxy… This discovery of the first bars means that galaxy evolution models now have a new path through bars to speed up the production of new stars in early times.”
The new images are part of the Cosmic Evolution Early Release Science Survey (CEERS), and their initial findings have been accepted for publication in The Astrophysical Journal Letters.
JWST is marking an exciting time for astronomers, and this was a promising start to 2023.
“I took one look at this data and said, ‘We’re letting go of everything else!'” says Jogee.
Learn more:
“James Webb Telescope Reveals Milky Way-Like Galaxies in Young Universe,” UT Austin.
Yuchen Guo et al., “First Look at z> 1 Bars in the Rest-Frame Near Infrared with JWST Early CEERS Imaging,” ArXiv Preprint.
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