Gary sent in the link https://www.sciencealert.com/physicists-have-just-revived-a-previously-debunked-alternative-theory-of-gravity … the theory does away with dark matter, a problem that has vexed physicists for some time. Modified Newtonian Dynamics MOND, was first aired in 1987 by Mordechai Milgrom. Since then dark matter has become a problem for mainstream physicists. Some scientists appear to have gone back to Milgrom as a means of doing away with something that can’t be seen and is entirely theoretical in concept. Dark matter is not required if you calculate the gravitational forces experienced by stars in a different manner from how Newtonian made the calculation. The research is published in the Monthly Notices of the Royal Astronomical Society.