FAST FACTS
What is it: Barred spiral galaxy Messier 61, also known as NGC 4303.
Where is it: 55 million light years away in the constellation Virgo.
When it was shared: October 28, 2025
Even before full-fledged scientific operations began, Vera K. Rubin Observatory in Chile has already helped astronomers find something remarkable. observatory first imagesrevealed in June, contained an in-depth look at Virgo Clusterthe closest and most studied cluster of galaxies. And in the lower right corner of the image, eagle-eyed astronomers saw something unexpected – a razor-thin stream of stars arcing away from one of the cluster galaxies.
The stream extends over about 50 kiloparsecs (about 163,000 light years), which is comparable to the diameter of our planet. Milky Way galaxy. This makes it longer than most famous stellar streams in our galaxy, whose length is only a few tens of thousands of light years.
The faint, galaxy-long trail is believed to consist of the remnants of a dwarf galaxy torn apart by M61's gravity. This decay could also have catalyzed star formation—a massive increase in the formation of new stars—that began in M61 about 10 million years ago.
The feature is reminiscent of the Sagittarius Stream, a long loop-like structure that surrounds the Milky Way and whose stars originated in the Sagittarius Dwarf Elliptical Galaxy, the scientists wrote in a study uploaded Oct. 28 to a preprint server. arXivto be published in the journal Notes of the American Astronomical Society.
The Sagittarius dwarf elliptical galaxy, a satellite of the Milky Way, is believed to have caused the formation of new spiral arms of stars within the Milky Way. All this suggests that most large galaxies can form by absorbing other, smaller galaxies around them.
“It is remarkable that the flow went undetected for a long time around the Messier Galaxy,” the authors write in the study. “We expect that with future Rubin data, a treasure trove of substructures will be discovered around other galaxies.”
Rubin is about to begin its 10-year Spacetime Legacy mission, during which it will create a high-definition time-lapse record of the universe.
More stunning space images can be found on our website. Archive of space photos of the week.
