Observational features of massive boson stars with thin disk accretion

TL;DR

This study models massive boson stars with scalar fields, simulates their observable appearance with thin disk accretion, and compares their features to black holes to identify potential observational signatures.

Contribution

It introduces new numerical solutions for massive boson stars with self-interaction and analyzes their observational features using ray-tracing, aiding in distinguishing them from black holes.

Findings

Boson stars exhibit multiple light rings and dark centers in disk images.

Light rings can deform into horseshoe or crescent shapes with observer position.

Polarized images reveal spacetime and disk magnetic field properties.

Abstract

In this paper, based on the action of a complex scalar field minimally coupled to a gravitational field, we numerically obtain a series of massive boson star solutions in a spherically symmetric background with a quartic-order self-interaction potential. Then, considering a thin accretion flow with a certain four-velocity, we further investigate the observable appearance of the boson star using the ray-tracing method and stereographic projection technique. As a horizonless compact object, the boson star's thin disk images clearly exhibit multiple light rings and a dark central region, with up to five bright rings. As the observer's position changes, the light rings of some boson stars deform into a symmetrical "horseshoe" or "crescent" shape. When the emitted profile varies, the images may display distinct observational signatures of a "Central Emission Region". Meanwhile, it shows that the corresponding polarized images not only reveal the spacetime features of boson stars but also reflect the properties of the accretion disk and its magnetic field structure. By comparing with black hole, we find that both the polarized signatures and thin disk images can effectively provide a possible basis for distinguishing boson stars from black holes. However, within the current resolution limits of the Event Horizon Telescope (EHT), boson stars may still closely mimic the appearance of black holes, making them challenging to distinguish at this stage.