Pair creation in the vortex-driven magnetic fields of black holes

TL;DR

This work investigates how pair creation via the gamma+B -> e^{±}+B channel in vortex-driven black hole magnetospheres affects the escape of high-energy photons. Using a dipolar magnetic field and an attenuation framework, it derives a minimum escape energy $\epsilon_m$ that grows with distance from the BH, predicting strong suppression of GeV photons near $10R_g$ and TeV photons near $100R_g$ for typical supermassive BHs. For a broad BH mass range ($M=(10^6-10^9)M_\odot$) at $r=100R_g$, the threshold shifts from $\sim250$ GeV to $\sim250$ TeV, illustrating the mass dependence of the effect. The study also estimates the resulting $e^{\pm}$ pair density, possible relativistic outflows, and annihilation signatures, suggesting observable indicators (absent or suppressed high-energy flux and annihilation lines) that could reveal a vortex-driven magnetic field, with implications extending to ultra-high-energy particle limits via a Hillas-type bound of up to $\sim10^{27}$ eV.

Abstract

We study the effects of pair creation on the radiation emerging from black holes under the assumption that the magnetic fields are vortex driven. In particular, for a sufficiently broad range of supermassive black holes, we investigated the energies at which photons undergo decay under the influence of a strong magnetic field, producing electron-positron pairs. Depending on particular physical parameters, it has been shown that in certain scenarios high or very high energy emission generated by black holes will be strongly suppressed, thus, will be unable to escape a zone where radiation is generated. In particular, photons with energies exceeding $\sim 1$ GeV will never leave the magnetosphere if they are generated at the scale 10$R_g$ and the threshold is of the order of $1$ TeV, if the emission is produced at $\sim 100\; R_g$. Analysing the process versus the black hole mass, assuming the region $100\; R_g$, it has been shown that for the considered lowest mass, the photons with energies $250$ GeV will never leave the black hole and for the considered highest mass the corresponding value is $\sim 250$ TeV.

Figures (1)

• Figure 1: On the left pannel we plot the radial dependence of $\epsilon_m$. The set of parameters is $M = 4\times 10^6 M_{\odot}$, $r_0\simeq 10R_g$, $\theta = 90^0$. On the right pannel we show the graph of $\epsilon_m (M)$. The set of parameters is the same as in Fig. 1a, except $r = 100 R_g$ and $M = (10^6-10^9)\times M_{\odot}$