Journal of Cosmology and Astroparticle Physics
ttps://doi.org/10.1088/1475-7516/2026/01/020
Hyeonmo Koo a and Jae-Weon Lee b
a Physics Department, University of Seoul, Seoul 02504, Korea
b Department of Electrical and Electronic Engineering, Jungwon University, 85 Munmuro, Goesan, Chungbuk 28024, Korea
E-mail: mike1919@uos.ac.kr, scikid@jwu.ac.kr
Abstract: We investigate the impact of repulsive self-interaction in ultralight dark matter
(ULDM) on dynamical friction in circular orbits in ULDM halos and its implications for the
Fornax dwarf spheroidal (dSph) galaxy’s globular clusters. Using the Gross-Pitaevskii-Poisson
equations, we derive the dynamical friction force considering soliton density profiles for both
non-interacting and strongly self-interacting ULDM. Our results show that self-interactions
reduce the dynamical friction effect further than both the non-interacting ULDM and standard
cold dark matter models. Furthermore, we derive the low Mach number approximation to
simplify the analysis in the subsonic motion, where the tangential component of dynamical
friction dominates. Applying these findings to the Fornax dSph, we calculate the infall
timescales of globular clusters, demonstrating that strong self-interaction can address the
timing problem more effectively. We constrain the parameter space for ULDM particle mass
and self-coupling constant, which are consistent with other constraints from astronomical
and cosmological observations.
Keywords: galaxy dynamics, dark matter theory, dwarfs galaxies
