Observations by the keen-eyed Webb Space Telescope have revealed a huge galaxy in the distant—which is to say early—universe.
The galaxy is a vibrant orange disk, dubbed the Big Wheel. Its life began within the universe’s first two billion years of existence; given the cosmos’ near-14-billion-year existence, that’s quite old.
The galaxy is remarkably developed for appearing so early in time, raising new questions about how galaxies form. The team’s research, published this week in Nature Astronomy, captures and explores the eerie beauty of the gargantuan structure.
“This galaxy is larger than any other kinematically confirmed disks at similar epochs and is surprisingly similar to today’s largest disks with regard to size and mass,” the team wrote in the paper. “Multiwavelength observations show that it lies in an exceptionally dense environment, where the galaxy number density is more than ten times higher than the cosmic average and mergers are frequent.”
In other words, the Big Wheel is in the universe’s old city: a very ancient and crowded part of the cosmos, in which galaxies intermingle, swapping star systems, asteroids, and dust in the process. The density of the environment may have catalyzed the galaxy’s evolution, providing it with the right conditions to accrete matter and swirl into its distinctively spiral shape.
Despite its size, the galaxy was a chance find. “Discovering a galaxy like the Big Wheel was incredibly unlikely,” said Themiya Nanayakkara, a senior scientist at Swinburne University of Technology’s JWST Australian Data Centre, in The Conversation. “We had less than a 2% chance to find this in our survey, according to current galaxy formation models.”
The Big Wheel’s stellar disk is about 30 kiloparsecs in diameter, or nearly 98,000 light-years across. For reference, the Milky Way’s diameter is about 100,000 light-years, about the same size as the Big Wheel.
The blue galaxy in the corner of the above image is just 1.5 billion light-years away, making the Big Wheel about 50 times more distant—a staggering margin that reveals just how big the Big Wheel is.
“Moreover, its dense environment suggesting the presence of a proto-cluster hints that its descendant might be one of the most massive members of today’s galaxy clusters,” the team wrote. “Nevertheless, further studies are needed to understand how common giant disks such as the Big Wheel were in dense environments at early cosmic epochs and whether their physical properties and number densities are consistent with the putative progenitors of today’s most massive cluster galaxies.”
More Webb observations will clarify how unique the Big Wheel is amid a morass of ancient galaxies, made visible by the space observatory’s unparalleled gaze.
