Observing the Shadows of Stellar-Mass Black Holes with Binary Companions

TL;DR

This paper explores the theoretical observation of black hole shadows in binary systems with stellar companions, proposing that future very-long-baseline interferometry could detect these shadows despite current limitations.

Contribution

It is the first study to calculate and visualize the shadows of stellar-mass black holes illuminated by stellar companions, expanding the scope of black hole shadow observations.

Findings

Shadows depend on binary orbit configurations.

Detection requires telescopes with extremely high resolution.

Current telescopes are insufficient for observing these shadows.

Abstract

The observation of the shadows cast by the event horizon of black holes on the light emitted in its neighborhood is the target of current very-long-baseline-interferometric observations. When considering supermassive black holes, the light source is the black hole's accretion disk, and therefore, the observation of the shadow may reveal information about the black hole and the accretion flow. We here study the shadows cast by stellar-mass black holes that are illuminated not by an accretion disk but by a stellar companion in a wide binary orbit. We calculate the shadows produced in such a configuration for the first time and show snapshots of the time-dependent shadow "movie" that is generated. We also study the minimal criteria for detecting and resolving such shadows with very-long-baseline-interferometric observations. We find that one would need telescopes capable of resolving apparent magnitudes greater than $33$ with baselines larger than $10^{6}$ km. Therefore, although very-long-baseline-interferometric efforts such as the Event Horizon Telescope would not be able to detect these shadows, their detection is possible with future telescopes in the next few decades.