BEC vortices as an observational signature of ultra-light bosonic dark matter

TL;DR

This study demonstrates, via numerical solutions of the Gross-Pitaevskii-Poisson equations, that rotating ultra-light bosonic dark matter halos develop a lattice of vortices that carry angular momentum and produce characteristic underdensity structures. It provides analytical TF-based baselines and a detailed simulation pipeline to evolve rotating ULDM cores, linking vortex properties to halo parameters such as mass and rotation rate. The authors propose gravitational lensing as an observational handle, showing that aligned vortices can induce regularly spaced brightness anomalies in lensed images, with detectability depending on vortex size and instrumental PSF. The work highlights a concrete, testable signature of BEC-ULDM and outlines a path for distinguishing vortex-induced lensing effects from subhalo overdensities, offering a practical route to probe the quantum nature of dark matter.

Abstract

Ultra-light bosonic dark matter (ULDM) is an interesting and promising dark matter candidate. While the wave-like nature of ULDM has been widely studied in the literature, we explore another distinctive feature of ULDM as Bose-Einstein Condensate (BEC) in this paper: the emergence of vortices in a rotating BEC-ULDM halos. Using numerical solution of the GPP equation, we demonstrate that a lattice of vortices ,underdensity columns that carry angular momentum, naturally forms in a ULDM halo under conditions similar to those of the Milky Way. Furthermore, we study the gravitational lensing by these vortices as a possible observational signature of BEC-ULDM. If the vortices are large enough and the halo's rotational axis align with the line of sight, regularly separated brightness anomalies can be produced, providing strong evidence for BEC-ULDM.

Figures (14)

• Figure 1: Comparison of the soliton density profile with (dashed line) and without(solid line) rotation. For the rotating case, we show the normalized density profile along the $x$ axis. The non-rotating density profile can be described by the TF approximation from Eq. \ref{['eq:TF']}. A vortex shows up as a local under-density region in the rotating soliton.
• Figure 2: Geometry of a gravitational lens system: $D_l, D_s, D_{ls}$ are the (angular diameter) distances from the observer to lens, observer to source, and lens to source, respectively. $\vec{\beta}$ and $\vec{\theta}$ are the angular positions of the source and image, respectively, relative to the line joining the observer and the center of the lens.
• Figure 3: Column density profile for a BEC halo with $\Omega = 3.51$ deg/Myr. The top (bottom) panel shows the top (side) view with the $z$-axis as the rotational axis.
• Figure 4: 3D illustration of the simulated result in Fig. \ref{['fig:omega45']}. Top, side, and vortex-only views are shown from top to bottom.
• Figure 5: Same as Fig. \ref{['fig:omega45']}, but for $\Omega = 0 \text{ deg/Myr}$ (top), $1.17 \text{ deg/Myr}$ (middle), and $1.95 \text{ deg/Myr}$ (bottom), respectively. The vortices in the upper right quadrant are outlined with dashed circles to guide the eyes..