DATE2025.08.08 #Press Releases

The galaxy was grainier than expected just after birth.

- "Cosmic Grapes" Shatter Conventional Wisdom on Galaxy Formation -

Summary

Findings

A research team including members from the University of Toronto, the University of Tokyo, and the National Astronomical Observatory of Japan has revealed that a faint, young galaxy that existed about 900 million years after the Big Bang exhibits a fragmented structure resembling a "bunch of grapes," composed of at least 15 compact star clusters. Despite this fragmented appearance, the galaxy as a whole demonstrates smooth rotational motion of gas. This discovery was made possible through high-precision observations that achieved unprecedented sensitivity and resolution by combining the capabilities of the James Webb Space Telescope (JWST), the Atacama Large Millimeter/submillimeter Array (ALMA), and gravitational lensing effects.

This kind of structure was unexpected, as it differs significantly from previous observations made by the Hubble Space Telescope (HST), standard JWST observations, and predictions from numerical simulations. The target galaxy is not exceptional in terms of size, mass, or other characteristics; it is considered a typical galaxy of its time. This suggests that similar structures may be hidden in many other galaxies from that era.

These findings have the potential to significantly revise our understanding of galaxy formation in the early universe.

The research paper detailing these results was published in the online edition of Nature Astronomy at 10:00 AM (BST) on August 7.
Professor Kotaro Kohno snd Associate Professor Kazuhiro Shimasaku of the Institute of Astronomy participated in this research.

Figure: Near-infrared image of the galaxy cluster RXCJ0600-2007 taken by JWST, which is causing strong gravitational lensing effects. The unprecedentedly high-resolution observation reveals for the first time a galaxy in the early universe, a cluster of more than 15 compact clusters, forming a "grape cluster"-like granular structure (Enlarged image, top left). (Image credit: NASA/ESA/CSA/Fujimoto et al.)

Related Links

Institute for Cosmic Ray Research, The UTokyo^{*only japanese}, National Astronomical Observatory of Japan

Journals

Journal name	Nature Astronomy
Paper Title	Primordial Rotating Disk Composed of ≥15 Dense Star-Forming Clumps at Cosmic Dawn