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

Abstract

The first direct detections of gravitational waves (GWs) from black hole (BH) mergers, GW150914, GW151226 and LVT151012, give a robust lower limit ∼ 70000 on the number of merged, highly-spinning BHs in our Galaxy. The total spin energy is comparable to all the kinetic energy of supernovae that ever happened in our Galaxy. The BHs release the spin energy to relativistic jets by accreting matter and magnetic fields from the interstellar medium (ISM). By considering the distributions of the ISM density, BH mass and velocity, we calculate the luminosity function of the BH jets, and find that they can potentially accelerate TeV-PeV cosmic-ray particles in our Galaxy with total power ∼ 10 37±3 erg s −1 as PeVatrons, positron factories and/or unidentified TeV gamma-ray sources. Additional ∼ 300 BH jet nebulae could be detectable by CTA (Cherenkov Telescope Array). We also argue that the accretion from the ISM can evaporate and blow away cold material around the BH, which has profound implications for some scenarios to predict electromagnetic counterparts to BH mergers.

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

“…We assume a power-law distribution for the number density for molecular clouds and cold H I in the range n 1 < n < n 2 with an index β, but assume a single density for the other three phases. The parameters H d and c s are the disc scale heights (Agol & Kamionkowski 2002) and effective sound speeds (Mii & Totani 2005;Ioka et al 2017) respectively. The filling fraction ξ of each phase obtained from our modelling depends on the location in the Galaxy (see Tsuna et al 2018 for details), and here the values of ξ at the Sun's location (r = 8.3 kpc) are shown.…”

“…where r is in kpc. The progenitor stars from the bulge are assumed to have a Maxwell-Boltzmann distribution with mean 130 km s −1 (Kunder et al 2012 Agol & Kamionkowski 2002;Ioka et al 2017;Tsuna et al 2018). The gas particle densities of the densest two phases, molecular clouds and cold H I, are assumed to obey a powerlaw of index 2.8 and 3.8 respectively, with a range of 10 2 cm −3 ≤ n ≤ 10 5 cm −3 and 10 cm −3 ≤ n ≤ 10 2 cm −3 respectively.…”

“…We assume an average particle mass of 2.72m p for molecular clouds and 1.36m p for atomic clouds. The effective sound speed of each phase, that includes the turbulent velocity which is important in cold phases, is set to c s = 3.7(n/100 cm −3 ) −0.35 km s −1 for molecular clouds (Mii & Totani 2005), c s = 150 km s −1 for the hottest H II phase, and 10 km s −1 for the other three phases (Ioka et al 2017).…”

“…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.…”