  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.

Cosmology and Nongalactic Astrophysics;High Energy Astrophysical Phenomena