Vera Rubin Observatory’s first image reveals hidden structure leading up to the Milky Way trailing behind nearby galaxies — Space Photo of the Week

Chile’s Vera C. Rubin Observatory is already helping astronomers discover remarkable things even before serious scientific activity begins. The observatory’s first images, released in June, included deep views of the Virgo cluster, the closest and best-studied galaxy cluster. Then, in the lower right of the image, eagle-eyed astronomers witnessed something unexpected – a razor-thin stream of stars arcing away from one of the cluster’s galaxies.

The barred spiral galaxy Messier 61 (M61, also known as NGC 4303) is well known and has been studied for decades. But only Rubin’s unique sensitivity to objects with low surface brightness was able to reveal this newly discovered star stream.

This stream spans approximately 50 kiloparsecs (about 163,000 light years), which is comparable to the diameter of the Milky Way galaxy. As such, its length is longer than most known star streams in the Milky Way, most of which are only tens of thousands of light-years.

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The faint breadcrumb trail the length of the galaxy is thought to consist of the remains of a dwarf galaxy that was torn apart by M61’s gravity. This breakup may also have catalyzed the starbursts (massive increases in new star formation) that began in M61 about 10 million years ago.

This feature is reminiscent of the Sagittarius Stream. The Sagittarius Stream is a long, looping structure that encircles the Milky Way and whose stars originate from the Sagittarius Dwarf Elliptical Galaxy, the scientists wrote in a research report uploaded to the preprint server arXiv on October 28.

The Sagittarius Dwarf Elliptical Galaxy, a satellite galaxy of the Milky Way, is thought to have formed a new star spiral arm within the Milky Way. All this suggests that most large galaxies may form by consuming other smaller galaxies around them.

“It is noteworthy that this flow has existed unnoticed for a long time around the Messier galaxy,” the authors write in their study. “We hope that future Rubin data will reveal a treasure trove of substructures around other galaxies.”

Rubin is about to embark on a 10-year space-time heritage research mission. This mission will create a high-resolution time-lapse record of the universe.

For more sublime space images, check out this week’s space photo archive.