Stellar stream

A stellar stream is an elongated structure of stars pulled from a star cluster or dwarf galaxy by gravity, often tracing the disrupted system’s orbit.

Tidal stripping: The removal of matter from an astronomical body by differential gravitational forces. A galaxy’s changing gravitational pull removes stars from a cluster or dwarf galaxy.
Sagittarius Stream: A vast trail of stars torn from the Sagittarius Dwarf Spheroidal Galaxy by the Milky Way. It is a prominent example of a stream still associated with a disrupting dwarf galaxy.
Galactic archaeology: The reconstruction of a galaxy’s formation history from the properties and motions of its stars. A stream retains chemical and orbital evidence about the system that was disrupted.
Stellar association: A loose grouping of young stars that share a birthplace but are not gravitationally bound. Unlike a stream, it is generally a young stellar grouping rather than tidal debris.
Tidal radius: The distance from an orbiting body within which its gravity can retain material against a larger body's tides. Stars beyond this boundary can escape their progenitor and join its stream.
GD-1: A narrow stellar stream in the Milky Way’s halo, identified in surveys of old stars. Its thin structure makes gaps and perturbations especially useful to study.
Galactic halo: The extended region surrounding a galaxy, containing stars, globular clusters, and dark matter. Many stellar streams orbit through the Milky Way’s halo.
Tidal tail: An elongated feature of stars and gas pulled from a galaxy during a gravitational interaction. The term often describes debris from interacting galaxies, while stellar stream commonly denotes a narrower stellar structure.
Orbital mechanics: The study of the motion of bodies under gravitational forces. Escaped stars spread along paths governed by their progenitor’s orbit.
Palomar 5: A low-mass globular cluster in the Milky Way with long tidal tails. Its tails show stars escaping a cluster to form a stream.

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