The Keen-Eyed Vera Rubin Observatory Has Discovered a Massive Stellar Stream

The Vera Rubin Observatory found a stellar stream coming from the M61 galaxy, a spiral galaxy in the Virgo Cluster. It extends for about 50 kpc, or 163,000 light years. The face-on image of M61 comes from the PHANGS (Physics at High Angular resolution in Nearby GalaxieS) survey. Credit: Romanowsky et al. 2025, RNAAS

The Vera Rubin Observatory (VRO) hasn’t yet begun its much-anticipated Legacy Survey of Space and Time. But it saw its first light in June 2025, when it captured its Virgo First Look images as part of commissioning its main camera. Those images are a sample of how the observatory will perform the LSST and feature the Virgo Cluster of galaxies.

While the galaxies in the Virgo Cluster have been well-studied, the powerful VRO has revealed new, previously unseen details. Astronomers have detected an enormous stellar stream emanating from one of the cluster’s galaxies, Messier 61 (NGC 4303.)

The discovery is in a new research letter titled “A stellar stream around the spiral galaxy Messier 61 in Rubin First Look imaging.” It’ll be published in the Research Notes of the American Astronomical Society, and the lead author is Aaron Romanowsky from the Department of Physics & Astronomy at San Jose State University. It is currently available on the arXiv preprint server.

The authors explain that among all the new detail revealed in the VRO images, a new stellar stream stands out. “One dramatic novelty is a long, narrow stellar stream extending Northward from the MW-like galaxy M61,” they write.

These types of streams are usually the remnants of a dwarf galaxy or a globular cluster that’s been torn apart by the larger galaxy’s tidal forces. The orbit stretches the stars into a stream. There are many known streams in the Milky Way, and they’re mostly tens of thousands of light years in length. But the newly-discovered stream at M61 dwarfs those ones: it’s about 163,000 light years long.

(Source: phys.org)