Spherical Boson Stars as Black Hole mimickers

We present spherically symmetric boson stars as black hole mimickers based on the power spectrum of a simple accretion disk model. The free parameters of the boson star are the mass of the boson and the fourth order self-interaction coefficient in the scalar field potential. We show that even if the mass of the boson is the only free parameter it is possible to find a configuration that mimics the power spectrum of the disk due to a black hole of the same mass. We also show that for each value of the self-interaction a single boson star configuration can mimic a black hole at very different astrophysical scales in terms of the mass of the object and the accretion rate. In order to show that it is possible to distinguish one of our mimickers from a black hole we also study the deflection of light.

💡 Research Summary

The paper investigates whether spherically symmetric boson stars can act as astrophysical mimickers of black holes by reproducing the power spectrum of a simple thin‑disk accretion model. Boson stars are described by a complex scalar field Φ with a potential V(Φ)=μ²|Φ|²+λ|Φ|⁴, where μ is the boson mass and λ is a quartic self‑interaction coupling. The authors solve the coupled Einstein–Klein‑Gordon (or Einstein–Klein‑Gordon‑Klein‑Gordon) equations numerically to obtain static, spherically symmetric configurations, mapping out the mass‑radius relation and stability curve for different (μ, λ) pairs.

The accretion disk model employed is the standard geometrically thin, optically thick disk (Novikov–Thorne type). The radiative efficiency η is set by the specific energy at the innermost stable circular orbit (ISCO): η=1−E_ISCO. For a non‑spinning Schwarzschild black hole, ISCO=6GM/c² and η≈0.057. By adjusting μ (and, when λ≠0, also λ) the authors tune the boson‑star spacetime so that its ISCO radius and corresponding E_ISCO match those of a black hole of the same total mass M. Consequently, the temperature profile T(r)∝