We call them black holes because their gravitational pull is so strong that even light is thought to be unable to escape it. Recently, however, Professors Ulf Leonhardt and Dr Germain Rousseaux have tested Stephen Hawking's theory: that these phenomena may not really be black after all.

Leonhardt and Rousseaux basically used a 30-meter-long water channel with a powerful pump on one end and a wave machine on the other to simulate a black hole's event horizon.

An event horizon is the place in the channel where the water begins to flow faster than the waves. The equivalent event horizon for a black hole would be the region where space seems to flow into the hole at the fastest speed.

Leonhardt and Rousseaux sent waves against the current, varying the water speed and the wavelength while filming the waves with video cameras. They wanted to see whether the waves show signs of particles and anti-particles, physics of black holes as theorized by Hawking.

The scientists reportedly observed traces of "anti-waves" of the water flowing in the channel. The flowing water didn't create anti-particles, though it may have created anti-waves whose movements ran counter to the movement of the regular waves.

Leonhardt and Rousseaux have acknowledged that their experiment doesn't completely agree with Hawking's theory. Thus, more research is needed to help them understand what happens at event horizons.