Spherical collapse of fuzzy dark matter

Abstract

It has been postulated that Fuzzy Dark Matter (FDM) could be a viable alternative to Cold Dark Matter (CDM). FDM is comprised of ultralight bosons which exist as a Bose-Einstein condensate. Due to the very low mass of FDM, the de Broglie wavelength of these bosons are of the order of kpc and the quantum effects manifest at those scales. Hence, unlike CDM, FDM experiences quantum pressure along with gravitational attraction. In this work, we investigate the gravitational collapse of a spherically symmetric FDM overdensity. We assume a power law density profile for an overdense region of FDM and derive an expression for the temporal evolution of a spherical shell in the non-interacting limit and use it to derive an expression for average overdensity contained in the spherical shell in an Einstein--de Sitter universe. Further, we numerically extend the analysis to the case of interacting bosons. Finally, we discuss the virialization of such an overdense region of non-interacting FDM and derive an expression for overdensity in the linear and the full theory. We compare our results with those obtained in the case of CDM and conclude with a discussion of the results.