Multi-wavelength emission from magnetically arrested disks around isolated black holes

TL;DR

This paper explores how isolated black holes with magnetically arrested disks emit detectable optical and high-energy signals, proposing methods for their identification using current and future astronomical surveys.

Contribution

It introduces the emission mechanisms of IBHs with MADs and suggests observational strategies for detecting and distinguishing them from other compact objects.

Findings

IBHs with MADs emit optical thermal synchrotron signals.

Non-thermal electrons produce flat-spectrum X-ray to gamma-ray emission.

Gaia and eROSITA can identify IBH candidates within 1 kpc.

Abstract

We discuss the prospects for identifying nearest isolated black holes (IBHs) in our Galaxy. IBHs accreting gas from the interstellar medium (ISM) likely form magnetically arrested disks (MADs). We show that thermal electrons in the MADs emit optical signals through the thermal synchrotron process while non-thermal electrons accelerated via magnetic reconnections emit a flat-spectrum synchrotron radiation in the X-ray to MeV gamma-ray ranges. The Gaia catalog will include at most a thousand of IBHs within $\lesssim 1$ kpc that are distributed on and around the cooling sequence of white dwarfs (WDs) in the Hertzsprung-Russell diagram. These IBH candidates should also be detected by eROSITA, with which they can be distinguished from isolated WDs and neutron stars. Followup observations with hard X-ray and MeV gamma-ray satellites will be useful to unambiguously identify IBHs.