Shape Shifting Light Dark Matter Solitons

Abstract

Dark matter consisting of a Bose-Einstein condensate (BEC) of ultralight particles forms solitons whose cored shape becomes increasingly cusped under the influence of a central point mass, such as a supermassive black hole. Here we present a unified analytic description of the resulting shape changes as a function of soliton mass fraction, spanning the hydrogenic to self-gravitating soliton limits. Solutions of the Schrödinger-Poisson equation are expressed as a sum of five Gaussians with numerically optimised coefficients, yielding closed-form expressions for soliton shape-dependent properties. Moreover, new mass-fraction-dependent scaling relations are used to approximate soliton size, density, and total mass directly in terms of observed stellar velocity dispersion and half-light radius. Applications to dwarf spheroidal (dSph) and ultra-faint dwarf (UFD) galaxies -- validated using a spherical-isotropic Jeans analysis -- show that the observed stellar density, velocity and enclosed mass are consistent either with dSph and UFD galaxies having different ultralight dark matter particle masses and no black holes, or with a single universal ultralight dark matter particle mass, requiring the presence of supermassive black holes in many UFD galaxies. These results, combined with a more detailed analysis of the radially resolved stellar velocity dispersions of Draco (dSph) and Segue~I (UFD), are found to be consistent with a universal ultralight dark matter particle mass of $m_0\approx 1.5\times 10^{-22}$\,eV/c${}^2$, to within a factor of~2. The results demonstrate the utility of soliton shape-shifting predictions in constraining dwarf galaxy dark matter profiles and revealing the possible presence of central black holes.

17 pages, 4 figures