Effects of Self-Interaction and of an Ideal Gas in Binary Mergers of Bosonic Dark Matter Cores

Abstract

We study binary mergers of dark matter cores in the Bose-Einstein condensate (BECDM) model. We include two scenarios: scalar self-interaction and the presence of a gravitationally coupled ideal gas. Using 3D simulations of the Gross-Pitaevskii-Poisson and Schrödinger-Poisson-Euler systems, we analyze the properties of the resulting remnants. We find that the final core-mass ratio reaches a stable average value after the merger. Repulsive self-interaction increases the mass of the final solitonic core, while attractive interaction enhances mass loss. In mergers involving an ideal gas, namely of fermion-boson stars, a stable solitonic core always forms in the bosonic component, even when the gas dominates, whereas the gas itself does not form a compact core. We explain these results using energy scalings and find that without self-interaction, equilibrium cores follow $E\propto -M^3$, which leads to an almost universal merger fraction. Self-interaction changes this scaling, because repulsive $g$ moves the system toward a milder $E\propto -M^2$ scaling and increases mass retention, while attractive $g$ strengthens binding and favors mass ejection. In the case of interaction with an ideal gas, this component only modifies the gravitational background and does not change the intrinsic scaling of the bosonic part. These results show that the merger outcome is not universal but controlled by the interaction strength, while solitonic BECDM cores remain robust across diverse environments including gas.

12 pages, 7 figures, contains corrections suggested by referees, submitted to Physical Review D

References in corpus (16)

• Ultralight scalars as cosmological dark matter
• Cosmic Structure as the Quantum Interference of a Coherent Dark Wave
• The impact of ultra-light axion self-interactions on the large scale structure of the Universe
• Scalar Field Dark Matter: non-spherical collapse and late time behavior
• Scalar Field Dark Matter: head-on interaction between two structures
• Cosmological evolution of a complex scalar field with repulsive or attractive self-interaction
• Cosmological Structure Formation and Soliton Phase Transition in Fuzzy Dark Matter with Axion Self-Interactions
• Deep zoom-in simulation of a fuzzy dark matter galactic halo
• Modifying PyUltraLight to model scalar dark matter with self-interactions
• The Effect of Boundary Conditions on Structure Formation in Fuzzy Dark Matter
• Bracketing the soliton-halo relation of ultralight dark matter
• Stationary solutions of the Schrödinger-Poisson-Euler system and their stability
• Fermion-Boson Stars as Attractors in Fuzzy Dark Matter and Ideal Gas Dynamics
• Construction and evolution of equilibrium configurations of the Schrödinger-Poisson system in the Madelung frame
• Single and merger soliton dynamics in scalar field dark matter with and without self-interactions
• Construction of ground state solutions of the Gross-Pitaevskii-Poisson system using genetic algorithms