Figure 1. Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). Dark matter can explain the 'flat' appearance of the velocity curve out to a large radius. Dark matter - Wikipedia

From

The Galaxies and the Dark Matter

José Luís Pereira Rebelo Fernandes

International Journal of Physics. 2021, 9(1), 36-41 doi:10.12691/ijp-9-1-4