November 8, 2025
2 min reading
Rubin Observatory discovers surprise ‘tail’ on iconic galaxy
First image from the Vera C. Rubin Telescope reveals a previously unnoticed feature of the M61 galaxy that could explain its mysterious properties
The Galaxy M61 sports a long stellar stream, which was not previously spotted.
NSF-DOE Observatory Vera C. Rubin/NOIRLab/SLAC/AURA/A. Romanowski you are at
Just months after its long-awaited debut, the Vera C. Rubin Observatory is beginning to deliver on its promise to rewrite cosmic history. The observatory’s colossal camera, perched atop a mountain in Chile, has yet to begin its official scientific study. But just by scanning its first test image, astronomers discovered a surprise: a trail of light – called a stellar stream – extending from a well-known galaxy, suggesting that the galaxy once tore apart a much smaller one.
“This is the first stellar flux detected from Rubin,” explains Sarah Pearson, an astrophysicist at the University of Copenhagen. “And this is just a precursor to the many, many features we’ll find like this.” The authors reported their findings in the American Astronomical Society Research Notes.
A tail that tells stories
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The galaxy, named Messier 61, was first spotted in 1779 in the Virgo galaxy cluster and has attracted the attention of astronomers ever since. Hosting a multitude of supernovae and producing new stars at a surprisingly high rate, Messier 61 is what is known as an explosion galaxy due to its rich stellar activity.
Astronomers have used powerful telescopes, including the James Webb Space Telescope and the Hubble Space Telescope, to unravel the structure of the galaxy. But “despite all these intense studies, no one had ever found this stellar stream,” explains Aaron Romanowsky, an astronomer at San Jose State University in California and author of the study.
After examining Rubin’s first image, captured by the world’s largest digital camera ever, the team filtered out excess light to reveal the galaxy’s stellar stream. The star trail measures 55 kiloparsecs or 180,000 light years, making it one of the longest streams discovered. It likely came from a dwarf galaxy that was torn apart by Messier 61’s gravity. Such an interaction could have stimulated star formation in Messier 61 and could begin to explain some of the galaxy’s anomalies, the authors note.
Rubin’s first image captures ten million galaxies, and it’s just an appetizer for observations to come. Over the next decade, Rubin will capture light from 20 billion galaxies, more than any other observatory so far.
“Every galaxy is expected to be surrounded by these currents. It’s a fundamental part of how galaxies are created,” says Romanowsky. “We just need to look weaker, and that’s the hope with Rubin.”
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