Polarization Images of Solitonic Boson Stars

TL;DR

This paper explores the polarization features of solitonic boson stars with accretion disks, revealing how polarization patterns relate to brightness, coupling strength, and scalar field, and proposing polarization as a distinguishing tool from black holes.

Contribution

It provides the first detailed analysis of polarization images of solitonic boson stars, highlighting their potential to differentiate these objects from black holes.

Findings

Polarization intensity correlates with optical brightness.

Coupling strength affects polarization distribution non-monotonically.

Polarization can penetrate the stellar interior, unlike in black holes.

Abstract

This study investigates the polarization characteristics of solitonic boson stars surrounded by a thin accretion disk. By comparing their polarization images with corresponding optical images, we find a positive correlation between the polarization intensity distribution in the polarization images and the brightness in the optical images. Consequently, the strongest polarization occurs at the location corresponding to the direct image. The influence of the coupling strength of the sixtic potential on the polarization intensity distribution is not monotonic, under strong coupling, the polarization will concentrated on the left side of the image as the coupling strength increases, whereas under weak coupling, it is more evenly distributed across the entire direct image as the coupling strength increases. Moreover, we find that as the initial scalar field increases, both the lensing image and photon ring become more prominent. However, the polarization intensity at these regions remains weak. Due to the absence of the event horizon in solitonic boson stars, the polarization vector can penetrate the stellar interior, unlike in black holes, where no polarization signals exist within the event horizon. Our numerical simulations clearly reveal this phenomenon, suggesting that polarization features may serve as an effective tool for distinguishing solitonic boson stars from black holes.