In a paper published today in Nature Astronomy, a team of astronomers, led by David A. Dunlap Department of Astronomy & Astrophysics assistant professor and Dunlap Institute for Astronomy & Astrophysics associated faculty Seiji Fujimoto, unveiled their discovery of a remarkably clumpy rotating galaxy that existed just 900 million years after the Big Bang. This finding will shed new light on how galaxies grew and evolved in the early universe.Nicknamed “the Cosmic Grapes,” the galaxy appears to be composed of at least 15 massive star-forming clumps—far more than current theoretical models predict could exist within a single rotating disk at this early time.
“It was truly astonishing to witness such a numerous star-forming clumps within a galaxy that is also smoothly rotating,” said Fujimoto, who was the primary investigator on the project, leading the observations and data analysis of the galaxy. “This is something we’ve never seen before in the early universe, and it challenges our current understanding of how galaxies form and evolve.”
The new observations were made using both the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), a radio telescope located in the Chilean Atacama Desert. The JWST’s NIRCam and NIRSpec instruments provided high resolution near-infrared images probing the detailed internal stellar distributions of the galaxy, while ALMA’s spectral observations were used to probe its internal gas motion.
Although the galaxy had appeared as a smooth, single disk-like object in previous images from the Hubble Space Telescope, the powerful resolution of JWST and ALMA, enhanced by gravitational lensing from the galaxy cluster “RXCJ0600-2007”, revealed a dramatically different picture: a rotating galaxy teeming with massive clumps, resembling a cluster of grapes.
The finding marks the first time astronomers have linked small-scale internal structures and large-scale rotation in a typical galaxy at cosmic dawn, reaching spatial resolutions down to just 10 parsecs (about 30 light-years).
This galaxy does not represent a rare or extreme system. It lies squarely on the “main sequence” of galaxies in terms of its star forming activity, mass, size, chemical composition—meaning it is likely representative of a broader population. If so, many other seemingly smooth galaxies seen by current facilities may actually be made up of similar unseen substructures, hidden by the limits of current resolution.
“Thanks to the extraordinary resolution of JWST and ALMA and the natural magnification from gravitational lensing,” said Fujimoto, “we were able to zoom into a typical early galaxy with unprecedented clarity — revealing its inner structure in a way that has never been possible.”
Because existing simulations fail to reproduce such a large number of clumps in rotating galaxies at early times, this discovery raises key questions about how galaxies form and evolve. It suggests that our understanding of feedback processes and structure formation in young galaxies may need significant revision. The Cosmic Grapes now offer a unique window into the birth and growth of galaxies — and may be just the first of many. Future observations will be key to revealing whether such clumpy structures were common in the universe’s youth.
A research briefing of the discovery can be found here.
About the Dunlap Institute for Astronomy & Astrophysics
The Dunlap Institute for Astronomy & Astrophysics in the Faculty of Arts & Science at the University of Toronto is an endowed research institute with over 80 faculty, postdocs, students, and staff, dedicated to innovative technology, groundbreaking research, world-class training, and public engagement.
The research themes of its faculty and Dunlap Fellows span the Universe and include optical, infrared and radio instrumentation, Dark Energy, large-scale structure, the Cosmic Microwave Background, the interstellar medium, galaxy evolution, cosmic magnetism and time-domain science.
The Dunlap Institute, the David A. Dunlap Department of Astronomy & Astrophysics, and other researchers across the University of Toronto’s three campuses together comprise the leading concentration of astronomers in Canada, at the leading research university in the country.
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