Early galaxies were shaped like surfboards and pool noodles, James Webb Space Telescope finds

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Young galaxies in the early universe adopted elongated shapes as they formed along filaments of the cosmic web, before evolving into more disc-like galaxies.

a view of various galaxies in deep space. they are multicolored and appear as various shapes
Astronomers using the James Webb Space Telescope found an array of odd shapes when the universe was 600 million to 6 billion years old. The galaxy shapes that dominate look flat and elongated, like pool noodles or surfboards. These two galaxy types make up approximately 50 to 80% of all the distant galaxies they studied – a surprise, since these shapes are rare closer to home. (Image credit: NASA, ESA, CSA, STScI, Steve Finkelstein (UT Austin), Micaela Bagley (UT Austin), Rebecca Larson (UT Austin))

Many small galaxies that existed early in the universe's history are elongated in a surfboard-like shape, pointing to the influence of the cosmic web of matter and constant mergers with other small galaxies, deep observations with the James Webb Space Telescope have found.

New research using the James Webb Space Telescope (JWST) found that dwarf galaxies in the early universe often look flat, either 'prolate' (elongated along one axis) or very narrow oblate ovals shaped like a surfboard, whereas others have a more frisbee-like oblate appearance. These galactic frisbees seem to grow more abundant as the universe ages, as do the compact, spheroidal-shaped galaxies.

"Roughly 50 to 80% of the galaxies we studied appear to be flattened in two dimensions," said Viraj Pandya, a Columbia University astronomer and lead author of a new paper describing the research, in a press statement. "[They] seem to be very common in the early universe, which is surprising since they are uncommon nearby."

Related: James Webb Space Telescope finds 2 of the most distant galaxies ever seen

The discovery was made using data from CEERS, or Cosmic Evolution Early Release Science, a JWST program to push back the veil and probe the lives of the oldest, faintest galaxies in the universe. It's an era spanning from 600 million years after the Big Bang to 6 billion years later, during which the galaxies that we see in the universe around us today formed, evolved and matured, from spirals like the Milky Way and the Andromeda Galaxy, to giant ellipticals such as M87.

Examples of distant galaxies captured by NASA's James Webb Space Telescope in its Cosmic Evolution Early Release Science (CEERS) Survey. Recent research of the CEERS field led by Viraj Pandya, a NASA Hubble Fellow at Columbia University in New York, showed that galaxies frequently appear flat and elongated, like pool noodles or surfboards (along the top row). Thin, circular disk-like galaxies, which resemble frisbees, are the next major grouping (bottom left and center). Finally, galaxies that are shaped like spheres, or volleyballs, made up the smallest fraction of their detections (bottom right). All of these galaxies are estimated to have existed when the universe was 600 million to 6 billion years old. (Image credit: NASA, ESA, CSA, STScI, Steve Finkelstein (UT Austin), Micaela Bagley (UT Austin), Rebecca Larson (UT Austin))

CEERS builds on previous work by the Hubble Space Telescope, which studied the early universe in its deep-field images and its CANDELS (Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey) program. Hubble found that massive galaxies in the early universe tended to take on the form of oblate spheroids, not dissimilar to the elliptical galaxies of today. Less massive and hence fainter galaxies were more difficult for Hubble to detect, but from what it could see, many of them took on an elongated appearance consisting of chains of brighter 'blobs', whereas other irregularly shaped dwarfs were nicknamed 'tadpoles', 'nuggets' or 'clumps'. 

The question was, given Hubble's limitations, was it seeing a true reflection of the shapes of smaller early galaxies? The JWST's greater vision has now found that Hubble's earlier discoveries hold true.

Kartheik Iyer, also of Columbia University, described how the greater vision and sensitivity of the JWST compared to Hubble is changing the study of galaxies in the early universe.

"Identifying additional categories for early galaxies is exciting — there's a lot more to analyze now," Iyer said in the press statement. "We can now study how galaxies' shapes relate to how they look and better project how they formed in much more detail."

A picture now emerges of how galaxies may have evolved and grown over time.

Matter is distributed throughout the universe primarily in a cosmic web of filaments that span the cosmos. These filaments are predominantly formed from dark matter, with a fraction of normal matter mixed in that forms the galaxies that we observe. The abundance of surfboard-shaped prolate galaxies could be explained by them forming inside haloes of dark matter that are elongated in alignment with their cosmic web filament. Since other dwarf galaxies would also be forming within that filament, mergers would take place along it, leading to the growth of elongated galaxies that look like chains. 

At top left, Webb's survey shows a classification that’s rare in the early universe, but common today: Galaxies that are shaped like spheres or volleyballs. At top right are flattened circular disks or frisbees, which are only slightly more common. The galaxy shapes that dominate during this early period look flat and elongated, like surfboards, shown at bottom left, or pool noodles, bottom right. This pair of classifications make up approximately 50 to 80% of all distant galaxies they've studied so far – a surprise, since these shapes are uncommon nearby. (Image credit: NASA, ESA, CSA, Joseph Olmsted (STScI))
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Across billions of years, the cosmic-web filaments disperse and grow more diffuse. The merger rate slows down and the fraction of prolate galaxies decreases as they start to spin and adopt a disc-like, oblate structure. Such oblate galaxies are seen to increase from 20 to 60% over time and for a given mass of galaxy. 

Similarly, spheroid galaxies also grow more abundant over time, as compact star-forming galaxies in the universe settle down to become the progenitors of the giant elliptical galaxies we see today, or the spheroidal bulges of massive spiral galaxies.

Understanding the evolution of galaxies over cosmic history is a key objective of the JWST. The new findings from CEERS indicate that hierarchical mergers — smaller galaxies merging with larger ones, along the aforementioned cosmic filaments — are key to understanding these varied galaxy shapes.

The findings are set to appear in a paper to be published in a future issue of The Astrophysical Journal.

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Keith Cooper
Keith Cooper
Contributing writer

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.