Intergalactic star

An intergalactic star is a star in the space between galaxies, no longer gravitationally bound to any galaxy. Such stars can be isolated or belong to diffuse populations around galaxy groups and clusters.

Tidal stripping: The removal of stars or gas from a galaxy by another object's gravitational forces. Gravitational encounters can pull stars out of their host galaxies and into intergalactic space.
Galaxy cluster: A gravitationally bound system containing many galaxies, hot gas, and dark matter. Clusters provide the dense gravitational environment in which large intergalactic star populations accumulate.
Virgo Cluster: A nearby galaxy cluster in the constellation Virgo, containing thousands of galaxies. Its planetary nebulae and diffuse light reveal stars between member galaxies.
Intracluster light fraction: The proportion of a galaxy cluster's total starlight found outside its member galaxies. This fraction estimates how much stellar material has been displaced into the cluster.
Galaxy merger: The collision and eventual combination of two or more galaxies under gravity. Mergers can fling stars onto orbits that leave the resulting galaxy.
Tidal tail: An elongated stream of stars and gas drawn from a galaxy by gravitational interaction. Tidal tails are visible structures through which stars can be dispersed beyond their former galaxy.
Fornax Cluster: A nearby, relatively compact galaxy cluster in the constellation Fornax. Its intracluster light offers a well-studied example of stars outside individual galaxies.
Planetary nebula luminosity function: The distribution of planetary nebula brightnesses, used to estimate distances to nearby galaxies. The bright end helps locate intracluster planetary nebulae and map their parent stars.
Ram-pressure stripping: The removal of a galaxy's gas as it moves through the hot plasma of a galaxy cluster. It strips gas rather than stars, clarifying which cluster process can liberate intergalactic stars.
Hypervelocity star: A star moving fast enough to escape the gravitational potential of its galaxy. Some become intergalactic, but their defining feature is exceptional speed rather than location.

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Astronomical objectRelated: Such stars challenge the assumption that stars belong to visible galactic structures.