The observation image of a soliton boson star illuminated by various accretions

TL;DR

This study uses ray-tracing simulations to analyze the observable optical signatures of solitonic boson stars under various accretion and illumination conditions, providing theoretical insights for distinguishing them from black holes.

Contribution

It introduces a detailed simulation framework for the optical appearance of soliton boson stars, exploring effects of coupling strength, inclination, and accretion models on observable signatures.

Findings

Images vary with coupling strength and inclination, showing direct, lensed, and nested ring features.

Photon orbits can be multiple, indicating complex lensing effects.

Redshift and Doppler effects dominate at different inclinations, affecting brightness and image morphology.

Abstract

In this paper, we explore the observable signatures of solitonic boson stars by employing ray-tracing simulations, with celestial spheres and thin accretion disks serving as illumination sources. By numerically fitting the metric form, we solve the geodesic equation for photons under the influence of the soliton potential, enabling us to simulate the optical appearance of the soliton boson star in two distinct regimes. In the weak coupling case (larger value of coupling parameter $\alpha$) with an initial scalar field $\psi_0$, the images on the screen predominantly show direct and lensed images, where $\psi_0$ and $\alpha$ modulate the image region size while the observation inclination $\theta$ controls morphological asymmetry. In the case of strong coupling (small value of $\alpha$), the images on the screen show a nested sub-annulus within the Einstein ring in the celestial model, whereas thin disk accretion models reveal higher-order lensing images indicative that photons are capable of orbiting the equatorial plane of the boson star multiple times. We also analyze how the effective potential and redshift factor depend on the correlation parameter. At low inclination($\theta<30^{\circ})$, the redshift is the dominant effect, the image is characterized by a dim central cavity enclosed by a bright ring. At high inclination ($\theta>60^{\circ})$, the Doppler effect becomes more pronounced, resulting in a substantial brightness disparity between the left and right sides of the optical image. These findings offer robust theoretical underpinnings for differentiating solitonic boson stars from black holes via high-resolution astronomical observations.