Jets and gamma-ray emission from isolated accreting black holes

Abstract

The large number of isolated black holes (IBHs) in the Galaxy, estimated to be 10^8, implies a very high density of 10^-4 pc^-3 and an average distance between IBHs of 10 pc. Our study shows that the magnetic flux, accumulated on the horizon of an IBH because of accretion of interstellar matter, allows the Blandford-Znajeck mechanism to be activated. Thus, electron-positron jets can be launched. We have performed 2D numerical modelling which allowed the jet power to be estimated. Their inferred properties make such jets a feasible electron accelerator which, in molecular clouds, allows electron energy to be boosted up to 1 PeV. For the conditions expected in molecular clouds the radiative cooling time should be comparable to the escape time. Thus these sources can contribute both to the population of unidentified point-like sources and to the local cosmic ray (CR) electron spectrum. The impact of the generated electron CRs depends on the diffusion rate inside molecular clouds (MCs). If the diffusion regime in a MC is similar to Galactic diffusion, the produced electrons should rapidly escape the cloud and contribute to the Galactic CR population at very high energies >100 TeV. However, due to the modest jet luminosity (at the level of 10^35 erg s^-1) and low filling factor of MC, these sources cannot make a significant contribution to the spectrum of cosmic ray electrons at lower energies. On the other hand, if the diffusion within MCs operates at a rate close to the Bohm limit, the CR electrons escaping from the source should be confined in the cloud, significantly contributing to the local density of CRs. The IC emission of these locally-generated CRs may explain the variety of gamma ray spectra detected from nearby MCs.Comment: 6 pages, accepted by MNRA

GW 150914-like black holes as Galactic high-energy sources

“…Therefore bright sources, i.e., massive BHs in dense ISM, are potential "PeVatrons" accelerating particles beyond PeV energy (Barkov et al 2012;Kotera & Silk 2016). We plot ε max on the upper horizontal axis in Figures 2 and 3.…”

X-ray detectability of accreting isolated black holes in our Galaxy

“…There have been many studies on the detectability of such accreting INSs (Ostriker et al 1970;Treves & Colpi 1991;Blaes & Madau 1993;Treves et al 2000;Perna et al 2003;Ikhsanov & Biermann 2007) and IBHs (Shvartsman 1971;Grindlay 1978;Carr 1979;McDowell 1985;Campana & Pardi 1993;Popov & Prokhorov 1998;Fujita et al 1998 Barkov et al 2012;Fender et al 2013;Ioka et al 2017;Matsumoto et al 2018). A number of observational searches have also been performed in the past for such accreting INSs and IBHs (Stocke et al 1995;Walter et al 1996;Wang 1997;Schwope et al 1999;Chisholm et al 2003;Muno et al 2006).…”

Radio emission from accreting isolated black holes in our galaxy

“…Blandford & Eichler 1987). The location of the termination shock corresponds to where the outflow's ram pressure balances the ISM inertia (Barkov et al 2012). Assuming the outflow is isotropic, its radius is…”

“…IBHs have thus mainly focused on accreting sources (Shvartsman 1971;McDowell 1985;Campana & Pardi 1993;Popov & Prokhorov 1998;Fujita et al 1998;Armitage & Natarajan 1999;Agol & Kamionkowski 2002;Maccarone 2005;Mii & Totani 2005;Barkov et al 2012;Fender et al 2013;Ioka et al 2017;Matsumoto et al 2018;Tsuna et al 2018). Although past searches using X-ray data have found candidates of accreting IBHs (Chisholm et al 2003;Muno et al 2006), no strong candidates are known at present.…”