Astronomers have discovered two giant galaxies from Earth trapped in a tug of war in the universe, 700 million light-years old. And for the first time in such a nearby galaxy, I saw a faint stream of stars being pulled from one side to the other.
Observations made on the Galaxy Cluster Abell 3667 revealed a faint, one million-year-old bridge of light on the star connecting two bright galaxies. Astronomers say the clusters are actually the result of two small clusters that began to fuse around a billion years ago, each with their own central galaxy. As these giants, and their satellite galaxies continue to fuse, the star bridges between them provide rare insight into the history of the cluster and the powerful gravity forces of play.
“This is the first time that this scale and size feature has been discovered in a local galaxy cluster,” said Ph.D. Anthony Engrat. The candidate at Brown University in Rhode Island said in a statement that he led a new paper explaining the observations. “It was a huge surprise to be able to image such a faint feature.”
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Bridges are made of light within clusters, or ICL, which is the diffuse glow from stars stripped from domestic galaxies by intense gravity. Englert and his team were able to detect this dim bridge by stacking 28 hours of observations over several years using the dark energy cameras from the Cerro Tololo Inter-American Observatory in Chile.
“It was just a happy coincidence that so many people have sabotaged Abell 3667 over the years, and we were able to stack all of those observations together,” Englert said in a statement.
At the top of the bridge is the lenticular (disk-shaped) Galaxy IC 4965, a small group of galaxies still falling in the cluster. At the bottom is Jo171. This is an impressive “jellyfish galaxy,” named after a long gas tendril from one side. When fused to the Abell 3667, Jo171 is stripped of gas and shuts down star formation in some of its ring-like structures, according to the statement.
Beyond visual aesthetics, Light Bridge also offers valuable probes of dark matter. This is an invisible material that is thought to account for about 80% of the universe’s mass. Light within clusters tends to track the same pathway as dark matter, and thus provides an indirect way to map its distribution, astronomers say.
“This distribution of light should reflect the distribution of dark matter, and therefore provides an indirect way to “see” dark matter,” Brown University co-author Ian del Antonio said in a statement.
The study highlights the types of discoveries that are expected to become routine soon with the Vera C. Rubin Observatory, which is scheduled to begin full operation later this year or early 2026. Rubin’s Legacy Survey of Space and Time (LSST) maps unprecedented details over a period of 10 years using the world’s largest digital camera.
“What we did is a little sliver of what Rubin can do,” Englert said in a statement. “It really intends to blow away widespread open research in ICL.”
This study is explained in a paper published on August 5th in the Astrophysical Journal.
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