Ultra-diffuse galaxies (UDGs) are unique to galactic clusters. They demonstrate a mechanism (rotating galactic space), which first by its absence and later by its development, simply and completely describes all phases of their formation and development within clusters. Galactic spatial rotation normally enables galactic gravity to hold high–speed stars in stable orbits within their local rotating space (without dark matter). UDGs developed in galactic clusters or other galactic groups where their orbits, through space, stymied early development of galactic spatial rotation, in some galaxies. This stymied rotation prevented its use, by pre-UDGs, to enable gravitational capture of their primordial stars and gases. And these stars and gases subsequently spiraled away, from impacted galaxies, in a whirlwind of high-speed mass. This whirlwind eventually pulled space into fast and broad rotation behind it. And this fast, new rotation not only enabled stable orbits (within local rotating space) for the small fraction of fast remaining stars, but also contributed extra speed to their orbits. These ultra diffuse, fast stars comprise recently discovered, UDGs. And some of the stars and gases, that the UDGs lost, eventually join into rich populations of globular clusters, which surround UDGs.

Ultra-diffuse galaxies, space, rotating space, galaxies, dark matter, galactic clusters, Coma