Twinkle twinkle dark star: Oscillating profiles from dark matter scalar solitons

TL;DR

This paper investigates oscillating scalar field configurations called oscillatons, exploring their potential observational signatures, especially their impact on accretion disk imaging and the possibility of detecting their 'twinkling' behavior with telescopes like the Event Horizon Telescope.

Contribution

It introduces the concept of oscillatons as time-dependent scalar field solutions and analyzes their observable effects on accretion disks and light deflection, proposing potential tests with current telescopes.

Findings

Stable oscillatory circular orbits exist within oscillatons.

Redshift oscillations produce a breathing-like image pattern.

Oscillation periods may be detectable by the Event Horizon Telescope.

Abstract

Real scalar fields, e.g. the axion, cannot condensate into stationary solitonic configurations to form star-like structures, eventually either dispersing or collapsing. However, by relaxing the stationarity condition on the metric, it has been shown that oscillatory solitonic solutions -- known as oscillatons -- exist. Oscillatons share several properties with boson stars, including comparable compactness and mass ranges. However, their time-dependent nature can lead to potentially discriminating observable signatures. In this work, we explore the observational properties of oscillatons. We find that stable oscillatory circular orbits exist, extending down to the center of the configuration, supporting the possibility of accretion disk structures within the star. We compute the deflection of light rays and verify that it is largely insensitive to the time dependence of the metric. Despite this, the oscillatory behavior of the redshift factor has a strong effect on the observed intensity profiles from accretion disks, producing a breathing-like image whose frequency depends on the mass of the scalar field. In fact, their oscillation period may lie within the observational windows of the Event Horizon Telescope for Sgr A$^{*}$ and M87$^{*}$, suggesting the possibility that this ``twinkling" behavior could be tested via near-horizon imaging of these objects.