Declining rotation curves of galaxies as a test of gravitational theory

Understand

Unlike Newtonian dynamics which is linear and obeys the strong equivalence principle, in any nonlinear gravitation such as Milgromian dynamics (MOND), the strong version of the equivalence principle is violated and the gravitational dynamics of a system is influenced by the external gravitational field in which it is embedded.

• This so called External Field Effect (EFE) is one of the important implications of MOND and provides a special context to test Milgromian dynamics.
• Here, we study the rotation curves (RCs) of 18 spiral galaxies and find that their shapes constrain the EFE.
• We show that the EFE can successfully remedy the overestimation of rotation velocities in 80\% of the sample galaxies in Milgromian dynamics fits by decreasing the velocity in the outer part of the RCs.