“This galaxy is spectacular for being among the largest spiral galaxies ever found, which is unprecedented for this early era of the universe,” Charles Steidel, the Lee A. DuBridge Professor of Astronomy at Caltech, said in a statement that gave a sense of the scale of the find. The James Webb Space Telescope (JWST) has discovered a massive spiral galaxy called “Big Wheel,” which upends deep-rooted beliefs about galaxy formation. This cosmic giant existed only two billion years after the Big Bang the universe was only about 15% of its current age then.
Big Wheel is not just huge it’s incredible. Its starry disk spans 100,000 light-years, larger than any other galaxy found from this epoch. The galaxy is also five times more massive than our own Milky Way, a scale that some physicists say is counterintuitive for galaxies of its epoch. Its spiral structure has survived such processes, which are normally destructive of a galaxy’s symmetry and caused high ‘merger rates’ and rapid accretion–in fact, during the bulk of the lives of galaxies.
The early growth of the galaxy was so swift that it was a child that started off as the biggest on the block and ate everybody else’s breakfast. Big Wheel’s formation challenges the slow, gradual and orderly processes that have historically been thought to assemble galaxies. Rather, its appearance seems to have developed corset on top of corset in a crowded cosmic neighborhood where numbers of galaxies were far more than tenfold their cosmic mean.
A galaxy’s environment might determine its size and structure. Big Wheel probably fared well in this unusually crowded region of space, given the frequency with which things collided and gas was crudely accreted. The incoming gas’s alignment with spin of the galaxy may have enabled it to quickly grow and retain its spiral shape. This peculiar environment offered the perfect setting for galaxies to expand in growth in rapid tempos, but the specifics of that accelerated evolution remain an enigma.
Astronomers using JWST’s Near-Infrared Spectrograph (NIRSpec) confirmed that Big Wheel is a rotating disk galaxy. Its rotation curve a distinctive feature of spiral galaxies re-confirms the local Tully-Fisher relationship, which connects a galaxy’s stellar mass with its rotation speed. Despite its youth, Big Wheel behaves like old galaxies found today in the universe, making it one of the best examples of the most extreme and early development of galaxies in the cosmos.
Vadim Semenov, a postdoctoral researcher at the Center for Astrophysics | Harvard & Smithsonian who did not take part in the study, said Big Wheel is one of the most extreme examples of galaxies forming during a time thought to be far more vigorous and chaotic. This finding contradicts existing cosmological models, which predict smaller, less mature galaxies at those redshifts.
And the serendipitous nature of the discovery adds yet another element to the intrigue. Weichen Wang, the study’s lead author, originally rejected Big Wheel as an invader from a later cosmic epoch. More analysis would reveal its true distance and age, showing it to be a galaxy that had grown really, really fast since the beginning of the universe. Wang’s surprise finding highlights the unpredictability of cutting-edge astronomy, where researchers often uncover treasure from unexpected observations.
The fate of Big Wheel has yet to be determined. Thanks to its crowded surroundings, future mergers can dramatically reshape it, potentially turning it into a giant elliptical galaxy, a fuzz ball of stars typically present in galaxy clusters. Such transformations are common in crowded regions of the cosmos, Steidel noted, but the details of a galaxy’s transformation into Big Wheel are unknown.
Big Wheel has important implications for our understanding of how galaxies form and evolve. This is probably a sign that the early universe was far more hospitable for the formation of large disk galaxies than we once suspected. “Further targeted observations are needed to build a statistical sample of giant disks in the early universe and thus open a new window on the early stages of galaxy formation.” Cantalupo said.
With the discovery of these two objects, astronomers have some work ahead of them to refine existing models to account for the potential for rapid galaxy growth in a dense environment. With more observations of massive, ancient galaxies like Big Wheel, astronomers hope to gain further insights into the processes that formed the earliest structures in the universe. The Big Wheel discovery is a great example for the kind of telling shower the universe could reveal and make us rethink cosmic history just using advanced telescopes such as JWST.
Big Wheel’s environment, its spiral structure, and its unexpected discovery emphasize the complexity and beauty of the early cosmos, inviting us to delve deeper and frame questions that challenge our current knowledge.
