Satellite galaxy

A galaxy gravitationally bound to and orbiting a more massive host galaxy. Its stars, gas, and dark matter can be altered by the host’s gravity and environment.

Dynamical friction: A drag-like effect that transfers orbital energy and angular momentum from a massive body to its surroundings. It can draw a satellite inward as its motion stirs the host’s dark matter and stars.
Host galaxy: A larger galaxy whose gravitational influence binds smaller orbiting galaxies. A satellite’s status and environment are defined relative to its host.
Large Magellanic Cloud: The largest satellite galaxy of the Milky Way, containing several billion stars. It is a massive, gas-rich satellite whose orbit and interaction with the Milky Way are actively studied.
Isolated galaxy: A galaxy with no nearby massive companion exerting a strong gravitational influence. Unlike a satellite, it evolves without orbiting a larger galaxy at close range.
Tidal stripping: The removal of matter from an astronomical body by differences in gravitational force across it. The host’s tidal field can peel stars and dark matter from an orbiting satellite.
Dark matter halo: A gravitationally bound distribution of dark matter surrounding a galaxy or galaxy cluster. The host halo supplies much of the gravitational well that keeps satellites in orbit.
Small Magellanic Cloud: A dwarf irregular galaxy orbiting the Milky Way and interacting with the Large Magellanic Cloud. Its ongoing interaction with another satellite demonstrates that satellites can form bound pairs.
Central galaxy: The dominant galaxy near the center of a dark matter halo. The central galaxy anchors the host system, while satellites orbit within it.
Ram-pressure stripping: The removal of gas from a moving galaxy by pressure exerted by surrounding hot gas. A satellite crossing its host’s hot halo can lose the gas needed to form stars.
Galaxy group: A gravitationally bound collection of galaxies smaller than a galaxy cluster. Groups provide common settings where galaxies orbit a dominant host.

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