Extremely Massive Galaxy Proto-Supercluster Smashes Distance Records
The ancestor to a ‘cluster-of-clusters’ of galaxies has a mass 5000 times that of the Milky Way and lies in one of the densest regions of the cosmic web ever observed
8 September 2026
An international team of astronomers has discovered the most distant progenitor to a galaxy supercluster ever. The discovery supports existing theories of how galaxy clusters evolve, and reveals how they are connected to the larger cosmic web. The study relies largely on data from the ODIN survey, conducted with the U.S. Department of Energy-fabricated Dark Energy Camera on the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope in Chile.
Galaxy clusters are the most massive gravitationally bound structures in the Universe. These colossal groupings of hundreds to thousands of galaxies span millions of light-years. They are held together by large concentrations of dark matter, which serves as the building block for the larger structure of the Universe.
Clusters that scientists observe relatively near to us in space and time are mature structures that evolved from what are known as ‘protoclusters.’ These protoclusters are enormous, loosely bound collections of galaxies that are in the process of merging together but have yet to settle into a stable cluster. By studying very distant protoclusters that formed when the Universe was relatively young, scientists can understand how modern galaxy clusters grew and evolved over time.
With this goal, an international team of scientists led by Vandana Ramakrishnan, a graduate student at Purdue University at the time of the study, looked billions of years back in time to search for these ancient galaxy cluster progenitors. The team presents their findings in a paper appearing in The Astrophysical Journal. “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,” says Ramakrishnan. “We also hope to get a better sense of how these protoclusters are connected to the larger cosmic web.”
Their study utilized data from the One-hundred-deg2 DECam Imaging in Narrowbands (ODIN) survey. This survey is conducted with the DOE-fabricated Dark Energy Camera (DECam), mounted on the NSF Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile, a program of NSF NOIRLab. With its large field of view and 570-megapixel resolution, DECam spent more than 100 nights over the last three years capturing deep images of a huge area of the Southern Hemisphere sky.
In total, the team identified 150 distant protoclusters that formed when the Universe was about 1–3 billion years old. They narrowed their focus to two clusters that showed a striking overdensity of galaxies, dubbed COSMOS-z3.1-A and COSMOS-z3.1-C [1]. The ODIN survey provided the 2D coordinates of these structures’ locations in the sky. However, to get a true sense of their galaxy distribution and how they fit into the large-scale cosmic web, a 3D perspective is necessary.
To map these structures in 3D, Ramakrishnan was joined by two other graduate students, Byeongha Moon (KASI) and Nicole Firestone (Rutgers), to lead follow-up observations using a suite of instruments called spectrographs. Rather than taking a 2D image of the sky, spectrographs 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 this study were acquired with the Dark Energy Spectroscopic Instrument (DESI) — a powerful multi-object spectrograph that can measure the distance to 5000 different galaxies simultaneously. The instrument was constructed with support from the DOE Office of Science and international partners and is operated with funding from DOE. The DESI project is managed by the DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab). The instrument is mounted on the NSF Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory (KPNO) in Arizona, a Program of NSF NOIRLab.
The team acquired additional spectra using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope in Chile, one half of the International Gemini Observatory, funded in part by the NSF and operated by NSF NOIRLab, as well as the DEep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II telescope located on Maunakea in Hawai‘i.
This animation shows a 3D model of the newly discovered galaxy proto-supercluster, COSMOS-z3.1-A. The light blue circles represent galaxies that are confirmed members of COSMOS-z3.1-A. The blue-to-purple gradient of the clouds surrounding them represents the density of galaxies throughout the proto-supercluster, with purple representing a higher density.
Credit: CTIO/NOIRLab/DOE/NSF/AURA/DSS2/NSF–DOE Vera C. Rubin Observatory. Acknowledgment: The original version of this 3D model was created by A. Ortiz (Purdue). Image Processing: T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), M. Zamani & D. de Martin (NSF NOIRLab). Motion Graphics: R. Proctor.
This study is one of the first to produce such detailed 3D maps of multiple distant protoclusters. The maps allowed the team to predict what kind of clusters COSMOS-z3.1-A and COSMOS-z3.1-C will evolve into. They found that both will evolve to be more massive than the largest known galaxy cluster in our local Universe, the Coma Cluster.
Moreover, they determined that COSMOS-z3.1-A is something even rarer than a protocluster, which is already quite rare. It is a proto-supercluster, or the ancestor of a ‘cluster of clusters’ of galaxies. Having been observed when the Universe was only 2.1 billion years old, this is the earliest, most distant proto-supercluster ever found [2], and it boasts an impressive mass 5000 times that of the Milky Way Galaxy. “COSMOS-z3.1-A represents the most extreme, most overdense regions of the Universe,” says Ramakrishnan. “We think there should be fewer than one such object for every 10,000 galaxy clusters!”
From their detailed 3D maps, the team concludes that these ancient protoclusters are very clumpy and irregular, and that they lie at the intersections of multiple cosmic web filaments. This is the first time scientists have directly observed such features in the distant Universe, and the observations agree with scientists’ expectations of how matter is distributed throughout the cosmos.
Current models suggest that structure formation proceeds in a 'bottom-up' manner, with smaller structures forming first and merging together to give rise to larger ones. It is likely that the clumpy substructure seen in the 3D maps is evidence of this bottom-up growth. The clumps will collapse together as the protoclusters evolve, giving rise to clusters similar to what we see in the local Universe, which are much rounder in shape.
With its wide area and depth, ODIN is well-positioned to uncover more of these massive cosmic structures in the distant Universe. “The 3D reconstruction methodology presented in this work will be a vital component of these efforts, enabling us to clearly distinguish the cores and outskirts of the protoclusters, as well as cosmic filaments feeding into them,” says Ramakrishnan.
The team looks forward to more discoveries in the next decade as NSF–DOE Vera C. Rubin Observatory conducts its groundbreaking Legacy Survey of Space and Time (LSST). By imaging the entire Southern Hemisphere sky every few nights, Rubin will create a rich dataset that will complement ODIN’s deep imaging of the overlapping region of sky. Together, the data will create a deep view of the nearby and distant Universe, allowing scientists to study galaxy cluster evolution across cosmic time.
Notes
[1] COSMOS is the designated name for the field where these structures were found, and z3.1 refers to their redshift, which is related to the number of years the light from the object has traveled to reach us. The COSMOS field is especially valuable to astronomers because it looks away from the crowded plane of our Milky Way and has been studied by many of the world’s leading telescopes.
[2] Another proto-supercluster, named Hyperion, has been identified in other studies. COSMOS-z3.1-A is identified at an even earlier time.
More information
This research was presented in a paper titled “ODIN: Characterizing the Three-dimensional Structure of Two Protocluster Complexes at z = 3.1” appearing in The Astrophysical Journal. DOI: 10.3847/1538-4357/ae8091
The team is composed of V. Ramakrishnan (Purdue University, USA), A. Ortiz (Purdue University, USA), B. Moon (Korea Astronomy and Space Science Institute [KASI], Republic of Korea), E. Jun (KASI, Republic of Korea), D. Schlegel (Lawrence Berkeley National Laboratory [Berkeley], USA), K. Lee (Purdue University, USA), J. N. Aguilar (Berkeley, USA), M. C. Artale (Universidad Andres Bello, Chile), D. Brooks (University College London, UK), M. C. Cerdosino (CONICET-UNC/Universidad Nacional de Córdoba, Argentina), R. Ciardullo (Pennsylvania State University, USA), T. Claybaugh (KASI, Republic of Korea), A. Cuceu (KASI, Republic of Korea), A. de la Macorra (Universidad Nacional Autónoma de México, México), A. Dey (NSF NOIRLab, USA), N. M. Firestone (Rutgers, USA), A. Font-Ribera (The Barcelona Institute of Science and Technology, Spain), J. E. Forero-Romero (Universidad de los Andes, Colombia), E. Gawiser (Rutgers, USA), E. Gaztañaga (Institute of Space Sciences/Institut d’Estudis Espacials de Catalunya, Spain/University of Portsmouth, UK), C. Gronwall (The Pennsylvania State University, USA), L. Guaita (Universidad Andres Bello, Chile), G. Gutierrez (Fermi National Accelerator Laboratory, USA), S. Hong (KASI, Republic of Korea), H. S. Hwang (Seoul National University [SNU], Republic of Korea), S. H. Im (SNU, Republic of Korea), P. T. Iribarren (Universidad Central de Chile, Chile), W. Jeong (KASI, Republic of Korea), D. Joyce (NSF NOIRLab, USA), A. Kumar (Universidad Andres Bello, Chile), C. Lamman (The Ohio State University, USA), M. Landriau (Berkeley, USA), S. Lee (SNU, Republic of Korea), J. Lee (Korea Institute for Advanced Study/KASI/SNU, Republic of Korea), A. Meisner (NSF NOIRLab, USA), R. Miquel (Institució Catalana de Recerca i Estudis Avançats/The Barcelona Institute of Science and Technology, Spain), J. Moustakas (Siena University, USA), S. Nadathur (University of Portsmouth, UK), G. Nagaraj (Laboratoire d’Astrophysique, Switzerland), J. Nantais (Universidad Andres Bello, Chile), N. Padilla (CONICET-UNC, Argentina), C. Park (Korea Institute for Advanced Study, Republic of Korea), W. Percival (University of Waterloo/Perimeter Institute for Theoretical Physics, CAN), F. Prada (Instituto de Astrofisíca de Andalucía, Spain), I. Pérez-Ràfols (Universitat Politècnica de Catalunya, Spain), G. Rossi (Sejong University, Republic of Korea), E. Sanchez (CIEMAT, Spain), J. H. Silber (Berkeley, USA), H. Song (Chungnam National University, Republic of Korea), D. Sprayberry (NSF NOIRLab, USA), G. Tarlé (University of Michigan, USA), F. Valdes (NSF NOIRLab, USA), Y. Yang (KASI, Republic of Korea), A. Zabludoff (University of Arizona, USA), and H. Zou (Chinese Academy of Sciences, China).
NSF NOIRLab, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona.
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The Dark Energy Camera (DECam) was designed specifically for the Dark Energy Survey (DES). It was funded by the U.S. Department of Energy (DOE) and was built and tested at DOE's Fermilab.
DESI is supported by the U.S. Department of Energy’s Office of High Energy Physics; the U.S. National Science Foundation, Division of Astronomical Sciences under contract to NSF NOIRLab; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico; the Ministry of Economy of Spain; and DESI member institutions. The DESI scientists are honored to be permitted to conduct astronomical research on I’oligam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation.
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Links
- Read the paper: ODIN: Characterizing the Three-dimensional Structure of Two Protocluster Complexes at z = 3.1
- Explore the 3D maps of multiple protoclusters
- Rutgers press release
- Purdue press release
- Photos of the Víctor M. Blanco 4-meter Telescope
- Videos of the Víctor M. Blanco 4-meter Telescope
- Images of DECam
- Images taken with DECam
- Images of DESI
- Videos of DESI
- Images of Nicholas U. Mayall 4-meter Telescope
- Videos of Nicholas U. Mayall 4-meter Telescope
- Check out other NOIRLab Science Releases
Contacts
Vandana Ramakrishnan
Purdue University
Email: ramakr18@purdue.edu
Josie Fenske
Public Information Officer
NSF NOIRLab
Email: josie.fenske@noirlab.edu
About the Release
| Release No.: | noirlab2622 |
| Facility: | Gemini South, NSF Nicholas U. Mayall 4-meter Telescope, NSF Víctor M. Blanco 4-meter Telescope |
| Instruments: | DECam, DESI, GMOS-S |
Facts Only
* The discovered structure is the ancestor to a ‘cluster-of-clusters’ of galaxies.
* Its mass is 5000 times that of the Milky Way.
* The discovery was made by an international team of astronomers.
* Data relied on the ODIN survey using the Dark Energy Camera on the Víctor M. Blanco 4-meter Telescope in Chile.
* The study aimed to understand the growth and evolution of galaxy clusters and their connection to the cosmic web.
* The team identified 150 distant protoclusters formed when the Universe was 1–3 billion years old.
* Two specific clusters focused on were COSMOS-z3.1-A and COSMOS-z3.1-C.
* Follow-up observations used spectrographs, including DESI, GMOS, and DEIMOS, to determine 3D positions.
* The team found that the structures are clumpy, irregular, and lie at intersections of cosmic web filaments.
* The evolved clusters will be more massive than the Coma Cluster.
Executive Summary
An international team of astronomers discovered the most distant progenitor to a galaxy supercluster, one with a mass 5000 times that of the Milky Way, located in one of the densest regions of the cosmic web. The research utilized data from the ODIN survey conducted with the Dark Energy Camera on the Víctor M. Blanco 4-meter Telescope in Chile. The study focused on finding ancient galaxy cluster progenitors to understand how modern clusters evolved and their connection to the larger cosmic web.
The team identified 150 distant protoclusters formed when the Universe was approximately 1–3 billion years old, narrowing their focus to COSMOS-z3.1-A and COSMOS-z3.1-C due to an overdensity of galaxies. To map these structures in three dimensions, the team used follow-up observations with spectrographs, primarily the Dark Energy Spectroscopic Instrument (DESI), supplemented by data from Gemini and Keck telescopes. The resulting 3D maps indicate that these ancient structures are clumpy and irregular, situated at the intersections of cosmic web filaments.
The study suggests that these protoclusters will evolve into structures more massive than the Coma Cluster and that they represent extreme, overdense regions of the Universe. The findings support the "bottom-up" model of structure formation, where smaller clumps merge to form larger clusters. Future efforts involve using data from the Vera C. Rubin Observatory to further map these cosmic structures and understand their evolution across cosmic time.
Full Take
The presentation of these ancient proto-superclusters as highly clumpy, filamentary structures directly supports the theoretical expectation of 'bottom-up' structure formation. The finding that COSMOS-z3.1-A is an extreme proto-supercluster, possessing a mass 5000 times that of the Milky Way at $z \approx 2.1$ billion years old, challenges simpler models of structure growth by emphasizing the role of concentrated overdensities already existing in the early Universe. The subsequent realization that these features lie at intersections of cosmic web filaments reinforces the geometry of the large-scale structure as predicted by cosmological models.
The methodology heavily relies on combining multi-wavelength data (ODIN imaging and redshift-based spectroscopy) to build 3D maps, which is a significant advance in mapping the evolving cosmic web structure compared to previous 2D surveys. The implication is that the seeds for the most massive local structures are embedded within these complex, clumpy progenitors, suggesting that the inhomogeneity of the early Universe is directly imprinted on the distribution of matter we see today. This shifts focus from just measuring cluster masses to understanding the physical process by which gravitational instability organizes dark matter into this filamentary web before it collapses into mature clusters.
What assumptions are baked into assuming a "bottom-up" growth? Does the observation of these highly irregular, clumpy structures not imply that structure formation is more stochastic or fractal than smooth, hierarchical accretion suggests? Furthermore, if there should be fewer than one such proto-supercluster for every 10,000 galaxy clusters, how does this specific finding constrain the parameters governing the initial density fluctuations in the very early Universe? What observational strategies are needed to test whether these observed filamentary intersections are purely a consequence of gravity or reflect some deeper underlying physical principle regarding dark matter distribution?
Sentinel — Human
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