Probing the detectability of electromagnetic signatures from Galactic isolated black holes

TL;DR

This paper investigates the potential electromagnetic signatures of isolated black holes in the Galaxy, modeling their accretion and outflows to assess detectability across multiple wavelengths and implications for dark matter.

Contribution

It presents a comprehensive model of electromagnetic emissions from IBHs considering accretion, outflows, and particle diffusion, highlighting their detectability and role in cosmic ray production.

Findings

Detectable mid-infrared and hard X-ray emission from IBHs in dense media.

Radio and millimeter emissions from outflow shocks could be observed.

IBHs may contribute up to 1% to Galactic cosmic rays at 1 PeV.

Abstract

Context: A large number of isolated black holes (IBHs) are expected to populate the Galaxy. However, only one has been confirmed by the analysis of a microlensing event, and no confirmed emission detection from an IBH has been reported so far. Aims: We analysed the detectability of electromagnetic signatures from IBHs moving in the Galaxy. Methods: We considered accretion from the interstellar medium onto an IBH and assumed the formation of an outflow. We modelled the accretion process and the interaction of the outflow with the surrounding medium on large scales, including mechanical feedback on the accretion process. Furthermore, we also calculated the emission from three different regions: the accretion region, the radiation from the outflow medium interaction structure, and the emission of relativistic particles that diffuse in the surrounding medium. Results: Multiwavelength emission associated with Galactic IBHs can be detected in systems moving through a very dense medium. Thermal emission from accretion could be observed in the mid infrared and in hard X rays with current and forthcoming observatories. Thermal and non thermal emission from the outflow medium shock could also be detected in the radio and millimetre ranges. Moreover, detection of the emission from particles diffusing in a dense medium could be feasible in gamma rays. Applying our model to the IBH associated with the gravitational microlensing event MOA2011BLG191 OGLE2011BLG0462, we inferred that radio and infrared detection of the IBH is plausible. Also, we derived that IBHs could be modest Galactic cosmic ray contributors, potentially reaching a 1% contribution at 1 PeV. Finally, by extending our model to primordial black holes, we conclude that efficient leptonic acceleration in their outflow medium interactions would rule them out as a major dark matter component.