Dark matter is also believed to be what holds galaxies (and galactic clusters) together by enveloping them in what are called dark matter halos. https://en.m.w

Dark matter is also believed to be what holds galaxies (and galactic clusters) together by enveloping them in what are called dark matter halos. https://en.m.wikipedia.org/wiki/Dark_matter_halo https://en.m.wikipedia.org/wiki/Dark_matter_halo