A method for evaluating models that use galaxy rotation curves to derive the density profiles

Abstract

There are some approaches, either based on General Relativity (GR) or modified gravity, that use galaxy rotation curves to derive the matter density of the corresponding galaxy, and this procedure would either indicate a partial or a complete elimination of dark matter in galaxies. Here we review these approaches, clarify the difficulties on this inverted procedure, present a method for evaluating them, and use it to test two specific approaches that are based on GR: the Cooperstock-Tieu (CT) and the Balasin-Grumiller (BG) approaches. Using this new method, we find that neither of the tested approaches can satisfactorily fit the observational data without dark matter. The CT approach results can be significantly improved if some dark matter is considered, while for the BG approach no usual dark matter halo can improve its results.

Testing gravity with wide binary stars like α Centauri

“…The currently prevailing cosmological paradigm (ΛCDM, Ostriker & Steinhardt 1995) is based on the assumption that General Relativity governs the dynamics of astrophysical systems. This can be well approximated by Newtonian gravity in the non-relativistic regime, covering for instance planetary motions in the Solar System and galactic rotation curves (Rowland 2015;de Almeida et al 2016). While the former can be well described by Newtonian gravity, this is not the case for the latter (e.g.…”

Brazilian Community Report on Dark Matter

“…At linear perturbative level, the assumptions considered include dark matter as a dissipative component due to a viscosity coefficient [102], with a velocity dispersion on the evolution of its perturbations [103], or with warmness represented by a reduced relativistic gas [104,105] Considering the dark matter profile, also the importance of the halo asphericity was stressed by [106]. Uncertainties on the overall dark matter density are also explored in the models beyond the ΛCDM [97,[107][108][109][110]. It has been noticed that one might indeed have deviations from the cold dark matter abundance inferred by Planck in models where dark matter and dark energy are coupled [111,112] On the particle physics side, several plausible new dark matter models have been proposed going from WIMPs [113], axions [33,114] to non-thermal dark matter [115], where the latter has an exciting connection with the IceCube data.…”

From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity

“…Despite these impressive successes, it is less clear whether GR can be extrapolated to the non-relativistic motions in the outskirts of galaxies and galaxy clusters. Wherever the relativistic corrections contribute insignificantly to the velocities in these systems, we will use the term 'Newtonian gravity' rather than GR because the two give very similar results for well-understood mathematical reasons (Rowland 2015;de Almeida et al 2016). The unexpectedly high velocity dispersion of galaxies relative to each other in the Coma Cluster could be the first evidence for a breakdown of Newtonian gravity (and thus GR; Zwicky 1933Zwicky , 1937, or it could indicate missing mass, though a combination of the two should not be lightly discarded.…”