ALMA and James Webb Space Telescope Shed Light on "Cosmic Grapes"

ALMA and JWST observations unveil unexpected details of rapid growth in a faint, newborn "grape-like" galaxy, similar to galaxies in the early universe following the Big Bang

Utilizing Atacama Large Millimeter/submillimeter Array (ALMA) and James Webb Space Telescope (JWST) observations amplified by gravitational lensing, a collaborative team has uncovered a primordial galaxy just 930 million years after the Big Bang (z=6.072), composed of at least 15 dense, star-forming clumps embedded within a rotating disk like a "Cosmic Grape". These clumps, with sizes ranging from 10 to 60 parsecs, dominate 70% of the galaxy's UV light, reshaping our understanding of early galactic structure formation. In total, more than 100 hours of telescope time were dedicated to this single system, making it one of the most intensively studied galaxies from the early universe.

Although the galaxy had appeared as a smooth, single disk-like object in previous Hubble Space Telescope observations, the powerful resolution of ALMA and JWST, enhanced by gravitational lensing, 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, and chemical composition, meaning it is likely representative of a broader population. If so, many other seemingly smooth galaxies seen by current facilities may be made up of similar unseen substructures, hidden by the limits of current resolution.

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.

Additional Information

The research paper titled "Primordial rotating disk composed of at least 15 dense star-forming clumps at cosmic dawn" by Fujimoto et al. appeared in Nature Astronomy.

This press release is based on the original press release by the National Radio Astronomy Observatory (NRAO), an ALMA partner on behalf of North America.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of ALMA's construction, commissioning, and operation.

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