Direct detection of black holes via electromagnetic radiation

Abstract

Many black hole (BH) candidates exist, ranging from supermassive ($\sim10^{6}$--$10^{10}$ M$_{\odot}$) to stellar masses ($\sim 1$--$100$ M$_{\odot}$), all of them identified by indirect processes. Although there are no known candidate BHs with sub-stellar masses, these might have been produced in the primordial Universe. BHs emit radiation composed of photons, gravitons and, later in their lifes, massive particles. We explored the detection of such BHs with present day masses from $10^{-22}$ M$_{\odot}$ to $10^{-11}$ M$_{\odot}$. We determined the maximum distances ($d$) at which the current best detectors should be placed in order to identify such isolated BHs. Broadly, we conclude that in the visible and ultraviolet BHs can be directly detected at $d\lesssim 10^7$ m while in the X-ray band the distances might reach $\sim10^8$ m (of the order of the Earth-Moon distance) and in the $\gamma$-ray band BHs might even be detected from as far as $\sim 0.1$ pc. Since these results give us realistic hopes of directly detecting BHs, we suggest the scrutiny of current and future space mission data to reach this goal.