Satellite galaxies of the Milky Way

Satellite galaxies of the Milky Way are galaxies gravitationally bound to and orbiting it. They range from tiny, faint dwarfs to the Large Magellanic Cloud.

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Large Magellanic Cloud: A dwarf irregular galaxy and the most massive satellite of the Milky Way. Its size and active star formation distinguish it from the faint dwarf satellites.
Dark matter halo: An extended distribution of dark matter surrounding a galaxy and contributing most of its gravitational mass. The Milky Way's halo supplies much of the gravity binding its satellites.
Lambda-CDM model: The cosmological model combining cold dark matter with a cosmological constant to describe the universe's evolution. It predicts that large galaxies form inside halos containing many smaller subhalos.
Ultra-faint dwarf galaxy: A very low-luminosity galaxy with few stars, typically found in the Milky Way's vicinity. New discoveries of these systems extend the satellite population into the faintest known regime.
Small Magellanic Cloud: A dwarf irregular galaxy that orbits the Milky Way alongside the Large Magellanic Cloud. Its interaction with the Large Magellanic Cloud has shaped both galaxies and surrounding gas.
Dynamical friction: A drag-like effect in which a massive body loses orbital energy through its gravitational wake in surrounding matter. It can cause massive satellites to spiral inward over time.
Hierarchical structure formation: The process by which small cosmic structures merge and accrete to build larger ones. The Milky Way's satellites are surviving remnants of this assembly process.
Too-big-to-fail problem: A mismatch between simulated massive dark matter subhalos and the observed central densities of bright satellite galaxies. The Milky Way's brightest dwarfs appear less dense than some simulations predict.
Sagittarius Dwarf Spheroidal Galaxy: A dwarf spheroidal galaxy currently being tidally disrupted by the Milky Way. Its stellar streams preserve evidence of a satellite being torn apart.
Tidal stripping: The removal of matter from an object by the differential gravitational pull of a larger body. The Milky Way strips stars and dark matter from satellites during close passages.