Rubin telescope uncovers giant stellar stream hidden behind nearby galaxy

Rubin Telescope Uncovers Giant Stellar Stream (Image: Romanowsky et al. 2025/RNAAS)

The Rubin Observatory has revealed an enormous stellar stream today. The structure trails behind galaxy M61 across deep cosmic regions. It stretches roughly 163,000 light years in visible length. Astronomers say the feature rivals the Milky Way in scale.

Its discovery surprised teams expecting routine calibration observations instead.

The stream remained invisible using previous astronomical survey telescopes. Rubin’s new camera detects extremely faint light with remarkable precision. Its first-light image exposed the subtle glow from scattered stars. Researchers confirmed the structure was real following careful checks. They described the discovery as an encouraging early demonstration.

Scientists believe the stream formed after a dwarf galaxy collided. M61 likely tore the smaller system apart using tidal forces. That violent interaction produced long arcs of stars now drifting outward. The event also triggered intense star formation within M61. Models suggest this burst happened around ten million years ago.

Such streams act like fossils recording ancient galactic interactions. Studying them helps astronomers understand how galaxies steadily grow. The Milky Way hosts similar streams from earlier minor mergers. Discoveries like this strengthen evidence for that hierarchical picture. Researchers expect Rubin will reveal many more faint structures soon.

Rubin will begin its decade-long Legacy Survey very soon. This programme will map the entire southern sky repeatedly. It aims to create the deepest time-lapse map ever assembled. Astronomers anticipate numerous discoveries hidden in low-brightness regions. The early success suggests a powerful era of cosmic archaeology.