Axionlike dark-matter winds driven by galactic baryon redistribution

Abstract

We examine solutions of the hydrodynamic equations for dark matter (DM) modeled as a Bose-Einstein condensate (BEC) with axionlike interaction, forming a spherically symmetric halo in dwarf galaxies. Small perturbations and decoherence of the BEC DM arise from changes in the gravitational background induced by subgalactic baryonic processes. Focusing on the events in the central region of a galaxy, overlapping with the stable DM core, we consider three scenarios: (i) expansion of a gaseous shell mimicking stellar explosions, (ii) collapse of a shell modeling star formation, and (iii) contraction of a stellar cluster toward the galactic center, driven by dynamical friction within a gaseous shell. Numerical parameters are extracted from observational data for NGC 2366. Our results show central DM density increases of 0.01 percent and DM wind velocities of up to several meters per second. A greater increase in density is observed at lower wind speeds and vice versa. These results raise the question of whether minor DM variations significantly affect star formation. In analyzing the fate of the cumulative impact of baryonic processes, we turn to the quantum excitation model with a discrete spectrum in finite volume. In the inhomogeneous DM halo, including unstable phase, metastable excitations associated with false vacuum states decay over 32 million years. This induces the decay of the system's evolutionary operator. Meanwhile, the Beliaev damping, originating from the decay of stable quasiparticles, emerges in the next order of perturbation.

Figures (10)

• Figure 1: Interstellar gas distributions in NGC 2366. The blue curves envelope cluster contributions, colored in gray and red. Circles in panel (a) are the data from Oh08.
• Figure 2: Stellar distributions in NGC 2366. The blue curves envelope the cluster contributions, colored in gray and red. Circles in panel (a) are the data from Oh08.
• Figure 3: Top row: gravitational potential differences $\Delta\Phi_{\rm b}$ (blue and green) and potential variations $\delta\Phi_{\rm b}$ (red and orange). Panel (a): changes induced by narrowing the width $\ell$ at fixed position $\breve{\xi}$. Panel (b): changes caused by a small leftward shift of $\breve{\xi}$ at fixed $\ell$. Bottom row: corresponding forces $F$, given by $-\partial_\xi\Delta\Phi_{\rm b}$ and $-\partial_\xi\delta\Phi_{\rm b}$, displayed in the same colors as their associated potential changes.
• Figure 4: Equilibrium DM density $\eta$ and the squared speed of sound $c^2_s$.
• Figure 5: DM perturbation density $\delta\eta$ and velocity $v$ during the expansion of gas cluster-1.