Declining rotation curves of galaxies as a test of gravitational theory

Hosein Haghi, Amir Ebadati Bazkiaei, Akram Hasani Zonoozi, Pavel Kroupa

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)


Unlike Newtonian dynamics which is linear and obeys the strong equivalence principle, in any non-linear 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 per cent of the sample galaxies in Milgromian dynamics fits by decreasing the velocity in the outer part of the RCs. We compare the implied external field with the gravitational field for non-negligible nearby sources of each individual galaxy and find that in many cases it is compatible with the EFE within the uncertainties. We therefore argue that in the framework of Milgromian dynamics, one can constrain the gravitational field induced from the environment of galaxies using their RCs. We finally show that taking into account the EFE yields more realistic values for the stellar mass-to-light ratio in terms of stellar population synthesis than the ones implied without the EFE.
Original languageEnglish
Pages (from-to)4172–4187
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date11 Apr 2016
Publication statusPublished - 1 Jun 2016
Externally publishedYes

Bibliographical note

Erratum: author name 'Pavel Kroupa' misspelled as 'Pavel Roupa'; corrected 13 June 2017.


  • methods: numerical
  • galaxies: kinematics and dynamics


Dive into the research topics of 'Declining rotation curves of galaxies as a test of gravitational theory'. Together they form a unique fingerprint.

Cite this