The Vera C. Rubin Observatory's first deep image of the Virgo cluster revealed a razor-thin stellar stream trailing Messier 61 (M61 / NGC 4303), about 55 million light-years away. The stream stretches roughly 50 kiloparsecs (≈163,000 light-years), comparable to the Milky Way's diameter and longer than most known streams in our galaxy. Researchers say it likely represents a dwarf galaxy shredded by M61 — an event that may have triggered a starburst ~10 million years ago — and that Rubin's upcoming 10-year LSST will uncover many more such faint structures.
Vera Rubin Observatory’s First Image Reveals Milky Way–Length Stellar Stream Trailing Messier 61
The Vera C. Rubin Observatory's first deep image of the Virgo cluster revealed a razor-thin stellar stream trailing Messier 61 (M61 / NGC 4303), about 55 million light-years away. The stream stretches roughly 50 kiloparsecs (≈163,000 light-years), comparable to the Milky Way's diameter and longer than most known streams in our galaxy. Researchers say it likely represents a dwarf galaxy shredded by M61 — an event that may have triggered a starburst ~10 million years ago — and that Rubin's upcoming 10-year LSST will uncover many more such faint structures.
02:10 AM, 11/17/2025Science
Rubin Observatory's first deep image exposes an enormous, faint stream of stars
Quick facts:
Object: barred spiral Messier 61 (M61 / NGC 4303)
Distance: ~55 million light-years (Virgo)
Study posted: Oct. 28, 2025 (arXiv; submitted to Notes of the American Astronomical Society)
Even before beginning full science operations, the Vera C. Rubin Observatory in Chile has produced a striking discovery. Its initial deep image of the nearby Virgo cluster — released in June — contains a razor-thin, very low surface-brightness stream of stars visible in the image's lower-right, trailing from the well-known barred spiral galaxy Messier 61.
The stellar ribbon spans roughly 50 kiloparsecs (≈163,000 light-years), a length comparable to the diameter of the Milky Way and longer than most stellar streams seen inside our own galaxy, which typically measure a few tens of thousands of light-years. Rubin's unprecedented sensitivity to diffuse, faint light is what made this feature detectable for the first time.
Researchers interpret the trail as the disrupted remains of a dwarf galaxy torn apart by M61's gravity. That violent encounter may also have triggered a starburst in M61 — a surge of new star formation that appears to have begun about 10 million years ago. The structure is reminiscent of the Milky Way's Sagittarius Stream, whose stars originated in an accreted dwarf galaxy.
"It is remarkable that the stream went long unnoticed around a Messier galaxy," the authors wrote. "We expect a treasure trove of substructures to be unveiled around other galaxies with future Rubin data."
The study describing the feature was uploaded to arXiv on Oct. 28, 2025, and is slated for publication in Notes of the American Astronomical Society. Rubin will soon begin its 10-year Legacy Survey of Space and Time (LSST), which will create a high-definition, time-lapse record of the sky and is expected to reveal many more faint, previously hidden structures — transforming our view of how large galaxies grow by cannibalizing smaller companions.
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