Dwarf galaxy

A galaxy with relatively few stars and low luminosity, often orbiting a larger galaxy or belonging to a galaxy group. Dwarf galaxies span a range of sizes, shapes, and gas content.

Stellar population: A group of stars described by shared properties such as age, chemical composition, or formation history. Differences in stellar ages and chemistry distinguish dwarf galaxy types and reveal their histories.
Tidal stripping: The removal of material from an astronomical object by another object's gravitational forces. A massive host can pull stars and dark matter from an orbiting dwarf.
Large Magellanic Cloud: A satellite galaxy of the Milky Way and the largest member of the Magellanic Clouds. Its active star formation and substantial size make it a nearby example of a dwarf irregular.
Ultra-diffuse galaxy: A galaxy with a large physical extent but very low surface brightness. Some ultra-diffuse galaxies are dwarf-like in stellar mass but unusually extended.
Missing satellites problem: The discrepancy between predicted and observed numbers of small satellite galaxies around large galaxies. The abundance of faint dwarfs tests predictions for small dark matter halos.
Dark matter halo: A gravitationally bound distribution of dark matter surrounding a galaxy or other cosmic structure. Its gravity can dominate a dwarf galaxy’s mass despite the galaxy’s few visible stars.
Ram-pressure stripping: The removal of gas from a galaxy as it moves through surrounding hot gas. This process can quench star formation in dwarfs inside galaxy groups and clusters.
Small Magellanic Cloud: A dwarf irregular galaxy orbiting the Milky Way. Its interaction with the Large Magellanic Cloud has shaped its gas and stellar structure.
Globular cluster: A dense, gravitationally bound collection of old stars orbiting a galaxy. Globular clusters can look like compact dwarfs, but generally lack dark-matter-dominated galaxy structure.
Too-big-to-fail problem: A mismatch between simulated massive subhalos and the central densities of observed satellite galaxies. Dwarf satellite dynamics challenge predictions for the most massive subhalos.

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