MOND is a modified theory of gravity. This study suggests that it works better than the theory of Dark Matter.
The MOND hypothesis says that Newton's force law must be tweaked at low acceleration -- 11 orders of magnitude lower than what we feel on the surface of Earth. Acceleration above that threshold is linearly proportional to the force of gravity -- as Newton's law says -- but below the threshold, no. At these tiny accelerations, the modified force law resolves the mass discrepancy.
"At stake now is whether the universe is predominantly made of an invisible substance that persistently eludes detection in the laboratory, or whether we are obliged to modify one of our most fundamental theories, the law of gravity," McGaugh continued.
The researchers tested MOND on quasi-spherical, very low-surface brightness galaxies that are satellites of Andromeda. In the cosmic scale, they are among the smallest galaxies, containing only a few hundred thousand stars. But with conventional gravity, they are inferred to contain huge amounts of dark matter.
"... we need to understand why MOND succeeds with these predictions. We don't even know how to make this prediction with dark matter."