Does the galaxy NGC1052-DF2 falsify Milgromian dynamics?

Abstract

A great challenge in current physics is to understand whether the observed internal dynamics of galaxies is due to dark matter or to a modification of the law of gravity. Recently, van Dokkum et al. reported that the ultra-diffuse dwarf galaxy NGC1052–DF2 lacks dark matter, and they claimed that this would — paradoxically — be problematic for modified gravity theories such as Milgromian dynamics (MOND). However, NGC1052–DF2 is not isolated, so a valid prediction of its internal dynamics in MOND cannot be made without properly accounting for the external gravitational fields from neighbouring galaxies. Including this external field effect, following Haghi et al., shows that NGC1052–DF2 is consistent with MOND.