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High-Velocity Cloud

(clouds in galactic halos)

A High-Velocity Cloud is a gas cloud within a Galactic Halo moving at a high velocity, e.g., Local Standard of Rest velocities in the 70-90 km/s range and with masses ranging up to millions of solar masses.

They're largely observed within the Milky Way, such as the Magellanic Stream, and in other nearby galaxies.