Tie Jun Cui and Qiang Cheng at the Southeast University in Nanjing, China, have built a "black hole" for microwave frequencies. The device may soon be extended to trap visible light, leading to an entirely new way of harvesting solar energy to generate electricity.

The electromagnetic "black hole" is made of 60 annular strips of so-called "meta-materials", which has previously been used to make invisibility cloaks. Each strip takes the form of a circuit board etched with intricate structures whose characteristics change progressively from one strip to the next. The outer 40 strips make up the shell and the inner 20 strips make up the absorber.

The structure makes ectromagnetic radiation curve inwards in a way which is analogous to the curvature of space-time near a black hole. At the point where the shell meets the core, the "permittivity" of the ring matches that of the core, so that light is absorbed rather than reflected.

"When the incident electromagnetic wave hits the device, the wave will be trapped and guided in the shell region towards the core of the black hole, and will then be absorbed by the core," says Jun Cui. "The wave will not come out from the black hole." The core converts the absorbed radiation into heat.

The researchers believe that they will be able to demonstrate an optical version of their device before the end of 2009.

An optical "black hole" would suck it in light and direct it at a solar cell sitting at the core, eliminating the need for large mirrors.