Hubble Spots Two Galaxy Clusters in the Process of Merging

By Matthew Williams - June 28, 2026 10:53 PM UTC | Observing
This NASA Hubble Space Telescope image features a swarm of galaxies in the galaxy cluster called CL0016+1609 or MACS J0018.5+1626. Credit: NASA/ESA/STScI/H. Ebeling/D. Coe/G. Kober
This NASA Hubble Space Telescope image features a swarm of galaxies in the galaxy cluster called CL0016+1609 or MACS J0018.5+1626. Credit: NASA/ESA/STScI/H. Ebeling/D. Coe/G. Kober

The venerable Hubble Space Telescope continues to survey the cosmos and capture images of amazing astronomical events. One of its latest finds features a galaxy cluster known as CL0016+1609 (MACS J0018.5+1626) that is very bright at X-ray wavelengths. By combining Hubble's optical observations with data from the Chandra X-ray telescope, astronomers discovered that this cluster is actually two clusters that are merging along our line of sight.

CL0016+1609 is one of the most extensively studied galaxy clusters in X-ray and radio wavelengths. The research team responsible for the image requested observation time using Hubble's Advanced Camera for Surveys (ACS) to measure the distribution of dark matter in the cluster. Their goal was to improve our understanding of how the merger of CL0016+1609 contributes to the large-scale structure of the Universe.

While Hubble cannot directly image Dark Matter, this mysterious mass is discernible by Hubble's optical and infrared instruments through the gravitational lensing it exerts on visible matter in the cluster. Data from Hubble's Wide Field Camera 3, taken as part of the ongoing Reionization Lensing Cluster Survey (RELICS), is also included in the image. Hubble's first infrared images were taken as part of this program, which included 46 galaxy clusters.

The gravitational lenses formed by these clusters also allowed astronomers to view another 300 high-redshift candidate galaxies. In this image, a faint vertical arc of a more distant galaxy is visible to the left of the large elliptical galaxies in the center. A brighter and shorter arc is also visible just above and to the right of the same elliptical galaxies.

Further Reading: NASA

Matthew Williams

Matthew Williams

Matt Williams is a space journalist, science communicator, and author with several published titles and studies. His work is featured in The Ross 248 Project and Interstellar Travel edited by NASA alumni Les Johnson and Ken Roy. He also hosts the podcast series Stories from Space at ITSP Magazine. He lives in beautiful British Columbia with his wife and family. For more information, check out his website.