5 Aug 2025-------------- Noirlab 2524

 

Cerro Tololo publishes spectacular image of a colossal galaxy cluster

The incredible detail achieved in the image provides key information about the past of galaxy clusters and anticipates the kinds of discoveries that will be possible with the new Vera C. Rubin Observatory.

 

A galaxy cluster in the midst of merging was captured in this detailed image obtained after 28 hours of observation by the U.S. Department of Energy's 570-megapixel Dark Energy Camera on the National Science Foundation's 4-meter Victor M. Blanco Telescope at Cerro Tololo, Chile. The image is a preview of the possibilities for unraveling the secrets of intracluster light that will be provided by the DOE-NSF Vera C. Rubin Observatory's Space-Time Legacy Survey.

Galaxy clusters are among the largest structures in the Universe, composed of hundreds of thousands of galaxies that have been gravitationally bound together over billions of years. Astrophysicists have long sought to understand the formation of these imposing figures because their history not only provides insight into how the Universe formed, but also provides some clues about the properties of dark matter , an invisible material that neither emits nor reflects light and that astronomers have found in high concentrations around galaxy clusters.

One of the clues astronomers look for to understand the history of a galaxy cluster is intracluster light —the faint glow emitted by stars that have been ripped from their home galaxies by the immense gravity of a forming galaxy cluster. These stars provide evidence of past galaxy interactions, but unfortunately, most telescopes and their cameras have a hard time capturing them.

The faint intracluster light of the galaxy cluster Abell 3667 shines brightly in this image from the U.S. Department of Energy’s 570-megapixel Dark Energy Camera ( DECam ) on the National Science Foundation’s Victor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory ( CTIO ), a program of NSF’s NOIRLab in Chile. Abell 3667 is more than 700 million light-years away. Most of the diffuse sources in this image are very distant galaxies, not foreground stars in our Galaxy.

Within Abell 3667, two smaller galaxy clusters are actively merging, as shown by the bright, yellowish bridge of stars that spans the center of this image. This junction connects the cores of the two galaxy clusters, which are known as the brighter galaxy cluster , and forms from the material stripped off the galaxies as they merge to form one massive conglomerate.

This brightly colored image is not only packed with distant galaxies, but faint foreground features are also illuminated by the long exposure time. Cirrus clouds in the Milky Way, or integrated flux nebulae , are faint, diffuse clouds of interstellar dust that can be seen as faint blue threads crisscrossing the image. These cirrus clouds are patches of dust illuminated by the combined light of stars in our Galaxy. They appear as diffuse, filamentary structures that can cover large areas of the sky.

This photograph, created from a total of 28 hours of observations, is the deepest image ever obtained of Abell 3667. Such a long exposure is necessary to detect the faint, diffuse glow of cirrus clouds, which normally only accounts for a few percent of the night sky brightness, as well as the even fainter intra-cluster light.

The way scientists study intracluster light will soon be revolutionized by the launch of the NSF–DOE Vera C. Rubin Observatory , a massive new science facility jointly funded by the National Science Foundation and the Department of Energy's Office of Science , which is expected to launch the Legacy Survey of Space-Time ( LSST ) project later this year .

Using the largest digital camera ever created, Rubin will image the entire southern night sky every night for 10 years. With the treasure trove of data the LSST survey will provide, there will be millions of high-resolution images of galaxy clusters. These images can be stacked to create ultra-long-exposure masterpieces, capable of revealing the intracluster light of a galaxy cluster.

The DECam image of Abell 3667 serves as a preview of what Rubin will be able to capture in LSST's eighth year, but instead of a single image of an individual galaxy cluster, Rubin will be able to capture this level of depth across the entire southern sky. Scientists hope that future studies of intracluster light using Rubin data will reveal new features and allow for more detailed studies of stellar populations with these characteristics.

 

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(B) Image of Abell 3667 with tags

(C) Excerpts From DECam's Deep View of Abell 3667