Abstract
If dark matter is composed of massive bosons, a Bose–Einstein condensation process must have occurred during the cosmological evolution. Therefore galactic dark matter may be in a form of a condensate, characterized by a strong self-interaction. We consider the effects of rotation on the Bose–Einstein condensate dark matter halos, and we investigate how rotation might influence their astrophysical properties. In order to describe the condensate we use the Gross–Pitaevskii equation, and the Thomas–Fermi approximation, which predicts a polytropic equation of state with polytropic index n=1. By assuming a rigid body rotation for the halo, with the use of the hydrodynamic representation of the Gross–Pitaevskii equation we obtain the basic equation describing the density distribution of the rotating condensate. We obtain the general solutions for the condensed dark matter density, and we derive the general representations for the mass distribution, boundary (radius), potential energy, velocity dispersion, tangential velocity and for the logarithmic density and velocity slopes, respectively. Explicit expressions for the radius, mass, and tangential velocity are obtained in the first order of approximation, under the assumption of slow rotation. In order to compare our results with the observations we fit the theoretical expressions of the tangential velocity of massive test particles moving in rotating Bose–Einstein condensate dark halos with the data of 12 dwarf galaxies and the Milky Way, respectively.
Highlights
The assumption of the existence of dark matter (DM) is one of the cornerstones of present day cosmology and astrophysics [1,2,3,4,5]
Various other astrophysical and cosmological observations have provided evidence for the existence of dark matter, like, for example, the recent determination of the cosmological parameters from the Planck satellite observations of the cosmic background radiation [10]. These observations have shown that dark matter cannot be explained by baryonic matter only, confirming the standard cold dark matter ( CDM) cosmological paradigm
To determine the coefficients A2l in the first order of approximation, we will write down the solution for the gravitational potential, and use the fact that it is continuous at the boundary of the dark matter halo
Summary
The assumption of the existence of dark matter (DM) is one of the cornerstones of present day cosmology and astrophysics [1,2,3,4,5]. In [81] the presence of vortices in a self-gravitating BEC dark halo, consisting of ultra-low mass scalar bosons was investigated, and it was pointed out that rotation of the dark matter imprints a background phase gradient on the condensate, which induces a harmonic trap potential for vortices. The question if and when vortices are energetically favored was considered, and it was found that vortices form as long as the self-interaction is strong enough It is the goal of the present paper to study the properties of the BEC dark matter halos in the presence of rotation. A comparison of our results with the observations is performed by fitting the theoretical expressions of the tangential velocity of massive test particles moving in rotating Bose–Einstein condensate dark halos with the data of 12 dwarf galaxies and of the Milky Way galaxy, respectively.
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