MOND (MOdified Newtonian Dynamics) models are popular among some scientist because they avoid one of the biggest problems in cosmology, dark matter. This misterious substance remains undetected although there is evidence from several observations that it must exist and in vast quantities. MOND models are able to explain some of these observations by modifying the laws of gravity. In particular, at cosmic distances MOND models propose that the gravitational acceleration does not decay as the inverse of the distance squared but at a smaller rate. This slower decay of the gravitational acceleration would effectively describe some of the observations without the need to invoke the existence of dark matter but it also has its own problems, like fine tunning of the parameters in the models. Together with some collaborators, we recently studied a particular galaxy behind the cluster MACS0416 that is gravitationally lensed (or bended) by another galaxy in the same cluster. We named this galaxy the Dragon Kick galaxy because it rejects the MOND hypothesis and confirms the pressence of a halo of dark matter around the lens galaxy. The Dragon Kick galaxy is shown above as a blue arc that is super-impossed on the legs of our would be Bruce Lee. Our results will be made public next week but basically we find that the lens galaxy (shown above as a yellowish edge-on galaxy emerging from the private region of our Bruce Lee) requires a halo around it that aligns perpendicularly with the lens galaxy in order to explain the shape of the lensed blue arc (the Dragon Kick galaxy) . The mass of this invisible halo (the dark matter) is larger than the mass of the lens galaxy and in agreement with what is expected from the standard model that assumes the existence of vast amounts of dark matter in the universe. More Dragon Kick galaxies are expected to be studied soon that could help in providing new clues about the nature of dark matter.
You can see the original paper here: http://arxiv.org/abs/1409.1578
cosmicspectator 