First Vera Rubin Observatory image reveals hidden structure as long as the Milky Way trailing behind a nearby galaxy — Space photo of the week

Features
By published

First-light images from the Vera C. Rubin Observatory have revealed a 163,000-light-year stream of stars emanating from the M61 galaxy, suggesting a violent past.

An image of a spiral galaxy on a splotchy black and white background with a stream of black material emerging from the galaxy
In its debut image, the Vera C. Rubin Observatory has revealed a vast stellar stream coming from the nearby galaxy M61. (Image credit: Romanowsky et al. 2025, RNAAS)
QUICK FACTS

What it is: Barred spiral galaxy Messier 61, AKA NGC 4303

Where it is: 55 million light-years away in the constellation Virgo

When it was shared: Oct. 28, 2025

Even before its full science operations have begun, the Vera C. Rubin Observatory in Chile has already helped astronomers find something remarkable. The observatory's first images, revealed in June, contained a deep view of the Virgo cluster, the closest and best-studied cluster of galaxies. And in the bottom-right of the image, eagle-eyed astronomers saw something unexpected — a razor-thin stream of stars arcing away from one of the cluster's galaxies.

The stream stretches roughly 50 kiloparsecs (about 163,000 light-years), which is comparable to the diameter of our Milky Way galaxy. That makes it longer than most known stellar streams in our galaxy, which are mostly only a few tens of thousands of light-years in length.

The faint, galaxy-length breadcrumb trail is thought to consist of the leftovers of a dwarf galaxy that was torn apart by M61's gravity. This breakup may also have been the catalyst for a starburst — a massive increase in new star formation — that began in M61 about 10 million years ago.

The feature is reminiscent of the Sagittarius Stream — a long, looping structure that encircles the Milky Way and whose stars originated in the Sagittarius Dwarf Elliptical Galaxy, scientists wrote in a study uploaded Oct. 28 to the pre-print server arXiv, which is due to be published in the journal Notes of the American Astronomical Society.

a figure showing different views of the stellar stream from M61

An image from the new paper showing a) galaxy M61 and its stellar stream, b) a zoomed-in view of the structure at the north end of the stream, and c) a view of the stream where it connects with the galaxy. (Image credit: Romanowsky et al. 2025, RNAAS)

A satellite galaxy of the Milky Way, the Sagittarius Dwarf Elliptical Galaxy is thought to have caused new spiral arms of stars to form within the Milky Way. All of this suggests that most large galaxies may form by consuming other, smaller galaxies around them.

"It is remarkable that the stream went long unnoticed around a Messier galaxy," the authors wrote in the study. "We expect a treasure trove of substructures to be unveiled around other galaxies with future Rubin data."

Rubin is about to embark on its 10-year Legacy Survey of Space and Time mission, during which it will create a high-definition time-lapse record of the universe.

For more sublime space images, check out our Space Photo of the Week archives.

Jamie Carter
Jamie Carter
Live Science contributor

Jamie Carter is a Cardiff, U.K.-based freelance science journalist and a regular contributor to Live Science. He is the author of A Stargazing Program For Beginners and co-author of The Eclipse Effect, and leads international stargazing and eclipse-chasing tours. His work appears regularly in Space.com, Forbes, New Scientist, BBC Sky at Night, Sky & Telescope, and other major science and astronomy publications. He is also the editor of WhenIsTheNextEclipse.com.

You must confirm your public display name before commenting

Please logout and then login again, you will then be prompted to enter your display name.