For the first time this week, images from the James Webb Space Telescope (JWST) revealed that star bars were present in some galaxies as early as 11 billion years ago. Bar stars 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, showing that the bars form very quickly and can persist for much of a galaxy’s life, influencing its shape and structure.
Stellar bars are regions of intense star formation that radiate from the galactic core. Through the motion of inner-orbiting stars, dust, and gas clouds, they accumulate as a wave of dense material that perpetuates itself and spreads slowly outward as it pulls the raw material inward. These regions become stellar nurseries that give birth to new stars at a rapid rate.
Six barred galaxies seen by JSWT as they would have appeared in the early universe, between 8.4 and 11 billion years ago (Gyr). Credit: NASA/CEERS/University of Texas at Austin.
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 oldest galaxy ever seen is at about 13.4 billion years).
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Most of these galaxies were previously imaged by the Hubble Space Telescope, such as EGS-23205, pictured below. (EGS stands for Extended Growth Strip, an area of the sky that has been extensively imaged and studied by international surveys). In the Hubble images, however, the bands are largely obscured.
Galaxy EGS23205 as seen by Hubble (left, taken in the near-infrared filter) and JWST (right, mid-infrared image). 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, dark objects. But it also has the advantage of using infrared rather than optical wavelengths. Light from older and more distant objects is “redshifted” along the electromagnetic spectrum, meaning JWST’s detectors can pick them up better than Hubble.
The infrared beam is also very effective at seeing through gas and dust, allowing JWST to pick out star nurseries in bars that would otherwise be obscured.
Shardha Jogee, a professor of astronomy at the University of Texas at Austin, explained the implications of these early-forming 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 in the EGS. Image credit: NASA, ESA, M. Davis (University of California, Berkeley), S. Faber (University of California, Santa Cruz), and A. Koeckmoer (STScI).
“Bars solve the galactic supply chain problem,” says Jogi. “Just as we need to bring raw material from the harbor to the inland factories that make new products, the bar powerfully transports gas into the central region, where the gas rapidly turns into new stars at a rate typically 10 to 100 times faster than in the rest from the galaxy… This discovery of early bars means that models of galaxy evolution now have a new path through bars to accelerate the production of new stars at early epochs.”
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 ushers in an exciting time for astronomers, and it’s been a promising start to 2023.
“I took one look at that data and said, ‘We’re rejecting everything else!'” says Jogi.
Find out more:
“James Webb Telescope Reveals Milky Way-Like Galaxies in the Young Universe,” UT Austin.
Yuchen Guo et al., “First Look at z > 1 Bands in the Rest-Frame Near Infrared with JWST Early CEERS Imaging,” ArXiv Preprint.
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