What’s a stellar stream?

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Stellar streams are created when stars are pulled from one galaxy by another. They are long, thin filaments of stars created by tidal forces. Most are too faint and distant to study, but a dozen have been named. The Arcturus stream is a remnant of a dwarf galaxy devoured by the Milky Way, and the Magellanic stream connects the Small and Large Magellanic Clouds. The Monoceros Ring is a ring-shaped stellar stream created when the Milky Way engulfed the Dog Major Dwarf Galaxy.

A stellar stream is created when the stars of one galaxy are pulled from their home galaxy by another. Stellar stream is a long, thin filament of stars produced by the stretching action of tidal forces. Only a dozen stellar streams have been named or studied in detail. As a phenomenon that only occurs on a galactic scale, most stellar streams are too faint and too distant to be studied in depth.

The most familiar stellar stream and one of the first to be confirmed as such is the Arcturus stream, located just 37 light-years away, containing the star Arcturus. The Arcturus stream is a remnant of a dwarf galaxy devoured by the Milky Way long ago. Over its lifetime, the Milky Way likely consumed dozens or even hundreds of smaller dwarf galaxies and continues to do so today. We even observe star clusters that look like the remains of the cores of devoured galaxies, such as the Omega Centauri star cluster. We know these are former galactic nuclei and not conventional open clusters because open clusters consist of stars that form around the same time, while a galactic core contains stars of widely varying ages.

One of the most studied stellar streams is the Magellanic stream, a stellar bridge connecting two of the closest galaxies to the Milky Way, the Small Magellanic Cloud and the Large Magellanic Cloud. Since the Magellanic Clouds are among the closest galaxies to ours, only 150,000 light-years away, we can observe individual stars in the “clouds” and their parallax, allowing us to build a 3D map of the galaxies and their interposed stellar flux .

Just as planets like Saturn cause dust to form in rings around them, some galaxies tear other dust apart and form them into rings as well. A ring-shaped stellar stream is the Monoceros Ring, created when the Milky Way engulfs a dwarf galaxy, the Dog Major Dwarf Galaxy, about 100 times smaller than itself.




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