New JWST picture exhibits giant spiral galaxies fashioned as early as 11 billion years in the past
Photos from the James Webb Space Telescope (JWST) this week showed for the first time that star bars were present in some galaxies as early as 11 billion years ago. Star bars are a distinctive 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 can form very quickly and persist for much of a galaxy’s lifetime, affecting its shape and structure.
Star bars are regions of intense star formation emanating from a galaxy’s core. Driven by the movement of inner orbiting stars, clouds of dust and gas, they build up as a wave of dense material that is self-propagating and slowly spreading outward while pulling raw material inward. These regions are becoming stellar nurseries, producing new stars at a rapid pace.
Six barred galaxies as seen by the JSWT as they would have looked in the early Universe 8.4 to 11 billion years (Gyr) ago. Photo credit: NASA/CEERS/University of Texas at Austin.
The new JWST images, presented Jan. 5 by the University of Texas at Austin, show six barred spiral galaxies over 8.4 million years old, two of which are over 11 billion years old (the oldest galaxy ever seen is about 13.4 billion years old). .
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Most of these galaxies have previously been imaged by the Hubble Space Telescope, such as EGS-23205, pictured below. (EGS stands for Extended Groth Strip, a region of the sky that has been extensively mapped and studied by international studies). In the Hubble images, however, the bars are largely obscured.
Galaxy EGS23205 as seen by Hubble (left, imaged in the near-infrared filter) and JWST (right, mid-infrared image). Photo credit: NASA/CEERS/University of Texas at Austin.
JWST has an advantage over Hubble in observing extremely old and distant galaxies, partly because its larger mirror can collect more light from distant, faint objects. But it also has an advantage due to the use of infrared instead of 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.
Infrared is also very effective at seeing through gas and dust, allowing JWST to see the stellar nurseries in the staffs that would otherwise be obscured.
Shardha Jogee, Professor of Astronomy at the University of Texas at Austin, explained the implications of these early forming bars for models of galactic evolution:
The position of the Extended Groth Strip (EGS) in the night sky. The galaxies newly observed by JWST lie within the EGS. Image credits: NASA, ESA, M Davis (University of California, Berkeley), S Faber (University of California, Santa Cruz), and A Koekemoer (STScI).
“Ingots solve the supply chain problem in galaxies,” says Jogee. “Just as we need to move raw materials from the port to factories inland that make new products, a bar of gas powerfully transports gas to the central region, where the gas is rapidly being converted into new stars, at a rate typically 10 to 100 times faster than the rest of the galaxy… This discovery of early bars means that galaxy evolution models now have a new way of using bars to accelerate the production of new stars in early epochs.”
The new images are part of the Cosmic Evolution Early Release Science Survey (CEERS) and their first results have been accepted for publication in The Astrophysical Journal Letters.
JWST heralds an exciting time for astronomers, and this has been a promising start to 2023.
“I looked at this data once and said, ‘Let’s drop everything else!'” says Jogee.
“The James Webb Telescope Reveals Milky Way-Like Galaxies in a Young Universe”, UT Austin.
Yuchen Guo et al., “First look at z > 1 bar in the near-infrared of the quiet frame using JWST Early CEERS Imaging,” ArXiv Preprint.