Effective galactic dark matter: first order general relativistic corrections

Abstract

Stationary, axisymmetric, dust sourced solutions of Einstein's equations have been proposed as fully general relativistic models for disc galaxies. These models introduce a novel physical element, i.e., a non-negligible dragging vortex emerging from a full consideration of the essential self-interaction of matter and geometry in general relativity, which might demand a profound recalibration of the inferred amount of dark matter in disc galaxies. Within this framework, we identify the correct observables for redshift-inferred rotation curves of distant galaxies, correcting previously overlooked mistakes in the literature. We find that the presence of the dragging vortex introduces non-negligible corrective terms for the matter density required to maintain a stable physical system. We present the first estimate of the dragging speed which is required to explain a non-negligible fraction of dark matter in disc galaxies. In particular, we show that a sub-relativistic dragging velocity of tens of kilometers per second in the neighbourhood of the Sun is sufficient to reduce the need of dark matter by 50% in the Milky Way. Finally, we find that the presence of such a dragging vortex also returns a net contribution to the strong gravitational lensing generated by the galaxy. Thus, we show that the considered class of general relativistic galaxy models, is not only physically viable, but suggests the need for recalibration of the estimated dark matter content in disc galaxies, with far reaching consequences for astrophysics and cosmology.