Generally, what we understand as “black” is the experience of zero perceived light. No light reaches our eye and so we experience blackness. Something has the property of being black because it doesn’t reflect (visible) light. We may put it in a box of other crayons like black is just some other color — you know, sharing space with burnt umber and neon carrot — but black also makes up its own corner of materials science and, at the same time, astronomy Welcome to the quest for “perfect black,” one that researchers at the University of Michigan appear to be winning with a new “magic black cloth” capable of cloaking an object’s three-dimensional properties.
The material, detailed in a new paper in the Applied Physics Letters absorbs 99.9-percent of visible light. The stuff is actually a carpet of sorts, made up of carbon nanotubes: imagine kind of a fuzzy forest of carbon strands in super-miniature. A coating of this stuff is about half the thickness of a sheet of paper. It exactly matches the refractive index of air, meaning that light travels through the material at the same speed as it travels through air. So, no light is scattered when it hits the material or the object it’s coating. Of course, an object covered in the perfect black coating will still cast a shadow, but put up against a black background, it’s pretty much gone.
JAY GUO, UNIVERSITY OF MICHIGAN.
“It was inspired by the idea to ‘cloak’ an object,” Jay Guo, the paper’s principle investigator, tells Motherboard. “We want to produce a scheme to produce ‘invisibility’ that [would] apply to large area and over a wide range of electromagnetic waves.” The stuff has all sorts of possibilities, however, from uses in display screens to the inside of telescopes to solar heating. Since it absorbs all light, it stands to be extremely efficient in that last task: all of the energy it absorbs gets turned to heat.
The sort of carbon nanotubes used in Guo’s magic black cloth exist naturally as well. In fact, they’re the result of most any combustion process involving metal, and we’ve found them on Earth in oil wells, polar ice caps, and elsewhere (within soot). Which means it certainly exists in space, too. Imagine what it could be hiding there. Planets, galaxies, dark matter.
“Since deep space itself is a perfect dark background, if a planet or star were surrounded by a thick, sooty atmosphere of light-absorbing carbon nanomaterial gases, it would become invisible due to the same principle,” Guo says in a U of M press release. “It would become totally dark to our instruments that rely on the detection of electromagnetic waves. Could this explain some of the missing matter in the universe?”
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Reach this writer at michaelb@motherboard.tv.
