Astronomers announced on 8 September 2026 the discovery of COSMOS-z3.1-A, the earliest and most distant galaxy proto-supercluster ever detected. Located where the Universe was just 2.1 billion years old, the colossal structure has a mass 5,000 times that of the Milky Way, providing a rare view of early cosmic web formation.
Peering back into the early Universe to a time shortly after the Big Bang, astronomers have uncovered an enormous cosmic structure taking shape in its infancy. Detected in a region observed when the Universe was only 2.1 billion years old, the newly identified object is known as COSMOS-z3.1-A. The international research team calls the discovery the ancestor of a giant cluster of clusters, measuring about 5,000 times the mass of the Milky Way according to NOIRLab data released on 8 September 2026.
Mapping the Ancient Universe with the ODIN Survey
Galaxy clusters represent the heaviest objects in the cosmos, featuring hundreds to thousands of galaxies held together by vast concentrations of invisible dark matter. While nearby clusters observed today are mature and settled, looking billions of years back in time reveals protoclusters—loose, chaotic groupings of galaxies still in the process of merging together. To track how these megastructures grew, researchers utilized data from the One-hundred-deg2 DECam Imaging in Narrowbands survey.
That survey relied on the Dark Energy Camera, fabricated by the U.S. Department of Energy and mounted on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a program of NSF NOIRLab. With its large field of view and 570-megapixel resolution, the instrument spent more than 100 nights across three years capturing deep-sky images of the Southern Hemisphere sky. The survey work identified roughly 150 distant protoclusters that formed when the Universe was between one and three billion years old.
Vandana Ramakrishnan, graduate student at Purdue University
An international team of scientists was led by Vandana Ramakrishnan, a graduate student at Purdue University at the time of the study, who presents their findings in a paper appearing in The Astrophysical Journal. Ramakrishnan outlined the core motivations of the research by stating, "With this project, we’re hoping to understand the growth of massive structures in the Universe and how they influence the evolution of galaxies within them," and adding, "We also hope to get a better sense of how these protoclusters are connected to the larger cosmic web." The team narrowed their focus onto two structures showing striking galaxy overdensities, designating them as COSMOS-z3.1-A and COSMOS-z3.1-C.
Transitioning From Two-Dimensional Coordinates to Three-Dimensional Mapping
While the narrow-band imaging survey provided two-dimensional coordinates for the targets, determining their true distribution required a three-dimensional perspective. Ramakrishnan was joined by two other graduate students, Byeongha Moon (KASI) and Nicole Firestone (Rutgers), to lead follow-up observations using advanced spectrographs. These instruments use properties of light to measure the distance to an object, allowing scientists to determine its position in 3D.
The majority of spectra used in the study were acquired with the Dark Energy Spectroscopic Instrument, a powerful multi-object spectrograph that can measure the distance to 5000 different galaxies simultaneously. Constructed with support from the DOE Office of Science and international partners, the instrument is operated with funding from DOE and managed by the DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), mounted on the NSF Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory.
Implications for Early Cosmic Evolution
The discovery supports existing theories of how galaxy clusters evolve, and reveals how they are connected to the larger cosmic web. By capturing the proto-supercluster in its active assembly phase, astronomers can examine the gravitational scaffolding built by dark matter before modern clusters settled into stable configurations.
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