Just what is this stuff we call Hawking radiation? Back in the 1990s, Stephen Hawking showed that black holes can emit tiny particles of radiation, which cause them to lose mass over time, gradually winking out of existence. It's the result of virtual particle pairs popping out of the quantum vacuum near a black hole.
Normally these virtual particles would collide and annihilate into energy, but sometimes one of the pair gets sucked into the black hole, resulting in an apparent violation of energy conservation. The mass of the black hole must decrease slightly as a result to counter this effect and ensure that energy is still conserved.
From the viewpoint of an outside observer - i.e., us - it would look like the black hole was giving off a steady stream of radiation.
How fast it evaporates depends on the black hole's size: the smaller it is, the faster it evaporates. Ergo, for those who might be worried, even in the event that the Large Hadron Collider in Switzerland really does produce mini black holes, they would be roughly the size of an electron, and would evaporate in mere fractions of a second. They would not gobble up the universe, no matter how many frivolous lawsuits are filed claiming the contrary.
Oh, but scientists can't be 100% certain of that, the fear mongers still claim, because they have yet to observe bona fide Hawking radiation in the actual universe. That's where the analogue black holes come in: these arise from lab experiments that use sound or light waves, for example, to imitate the physical properties of the event horizon, the point of no return for any object unfortunate enough to cross that invisible line.
In recent years, physicists in various labs scattered around the globe have become very adept at mimicking the signature behavior of black holes - at least from a mathematical standpoint - in various ways. For instance, Ulf Leonhardt and the gang at the University of St. Andrew's in the United Kingdom have created analogue black holes using laser pulses and optical fibers. And William Unruh has worked with scientists at the University of British Columbia to create a water-wave version of an event horizon.
The Italian team, headed by Francesco Belgiorno, used ultrashort, very intense pulses of infrared laser light focused onto a piece of glass, trillions of times more intense than sunlight. This boosted the refractive index of the glass - the property that determines how quickly light can move through a material - slowing down the light and acting as a high barrier that photons are unable to surmount. It acts just like the event horizon of a black hole.
According to New Scientist, here's what they did next:
To see if this lab-made event horizon was producing any Hawking radiation, the researchers placed a light detector next to the glass, perpendicular to the laser beam to avoid being swamped by its light. Some of the photons they detected were due to the infrared laser interacting with defects in the glass: this generates light at known wavelengths, for example between 600 and 700 nanometres.
Personally, I'm a fan of such research. Recreating simplified analogues for huge cosmic systems on a tabletop is inherently cool. And it's true that scientists can learn a great deal about black holes by studying these sorts of models.
If the Italian team's findings are borne out by eagle-eyed colleagues conducting subsequent experiments - especially if those experiments can detect whether or not the pairs of photons that get separated are entangled - this would be an exciting experimental confirmation of one of Hawking's most famous theoretical predictions.
But observing Hawking radiation emitting from an actual black hole? That would be priceless.
Images: Hawking radiation (NASA), Stephen Hawking (AP)