Mini-hole made of metamaterials ensnares microwave light.
Physicists have created a black hole for light that can fit in your coat pocket. Their device, which measures just 22 centimetres across, can suck up microwave light and convert it into heat.
The hole is the latest clever device to use 'metamaterials', specially engineered materials that can bend light in unusual ways. Previously, scientists have used such metamaterials to build 'invisibility carpets' and super-clear lenses. This latest black hole was made by Qiang Chen and Tie Jun Cui of Southeast University in Nanjing, China, and is described in a paper on the preprint server ArXiv1.
Black holes are normally too massive to be carried around. The black hole at the centre of the Milky Way, for example, has a mass around 3.6 million times that of the Sun and warps the very space around it. Light that travels too close to it can become trapped forever.
The new meta-black hole also bends light, but in a very different way. Rather than relying on gravity, the black hole uses a series of metallic 'resonators' arranged in 60 concentric circles. The resonators affect the electric and magnetic fields of a passing light wave, causing it to bend towards the centre of the hole. It spirals closer and closer to the black hole's 'core' until it reaches the 20 innermost layers. Those layers are made of another set of resonators that convert light into heat. The result: what goes in cannot come out. "The light into the core is totally absorbed," Cui says.
"I am very impressed," says John Pendry, a theoretical physicist at Imperial College London. Pendry says that the black hole is yet the latest example of the many strange devices that can be built with metamaterials. But, he adds, it is not a perfect black-hole analogy. The enormous gravity of real black holes causes them to emit an eerie quantum glow, known as Hawking radiation. "The optical device reported in this paper has no internal source of energy and therefore cannot emit Hawking radiation," Pendry says.
Nevertheless, Cui says that the hole could prove useful. By the end of the year his team hopes to have a version of the device that will suck up light of optical frequencies. If it works, it could be used in applications such as solar cells.
Cheng, Q. & Cui, T. J. http://arxiv.org/abs/0910.2159v1 (2009).
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Brumfiel, G. Researchers create portable black hole. Nature (2009). https://doi.org/10.1038/news.2009.1007