A newly published paper in The Astrophysical Journal talks about the possibility of using a high-powered laser to scan for black holes by detecting the concentric rings of light that would be reflected. The authors of the paper say this technique is similar to detection of MACHOS (massive compact halo objects; possible repositories of dark matter) and could provide the first direct observations of black holes close to our solar system.

 

 

ABSTRACT

Shine a flashlight on a black hole, and one is greeted with the return of a series of concentric rings of light. For a point source of light, and for perfect alignment of the lens, source, and observer, the rings are of infinite brightness (in the limit of geometric optics). In this manner, distant black holes can be revealed through their reflection of light from the Sun. Such retro-MACHO events involve photons leaving the Sun, making a :pi: rotation about the black hole, and then returning to be detected at the Earth. Our calculations show that although the light return is quite small, it may nonetheless be detectable for stellar-mass black holes at the edge of our solar system. For example, all (unobscured) black holes of mass M or greater will be observable to a limiting magnitude m, at a distance given by 0.02 pc * [10^(m-30)/2.5(M/10M_sun)²]^1/3. Retro-MACHOs offer a way to directlyimage the presence of black holes and would be a stunning confirmation of strong-field general relativity.

-Holz & Wheeler, Retro-MACHOs: [pi] in the Sky? The Astrophysical Journal, 578:330-334, 2002 October 10 ©2002.

Sounds good, but it would take years waiting for the light to get there and return.

Not that long, it's just looking right at the edge of our solar system.