  A great challenge in present-day physics is to understand whether the
observed internal dynamics of galaxies is due to dark matter matter or due 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 like Milgromian dynamics (MOND). However, NGC1052-DF2 is not isolated,
so that 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.
