Can lasers be caught in a waterfall

Black Hole, homemade

St. Andrews / Vienna - Scientists have been simulating the legendary black holes on computers for a long time. At a time when the disappearance of matter on the event horizon of a Black Hole has probably been directly observed for the first time, British physicists want to recreate these cosmic omnivores as real models. For this purpose, light is strongly slowed down by means of a laser and then trapped in liquids. According to the theory, black holes can be formed when stars of a certain size collapse. The density and attraction of this accumulation of mass are so high that anything that ever gets into the black hole is trapped in it forever. Even light can no longer escape due to the enormous gravity, so the hole is also invisible - just "black". Now the physicists have no hope of ever getting such a mass together in the laboratory, but the physicists working with Ulf Leonhardt from the University of St. Andrews (Great Britain) have come up with a trick to simulate the effects of a black hole. The researchers are particularly interested in the phenomenon of the black hole as a light trap. Leonhard wants to use liquids as such light suckers in the laboratory. For this, only the speed of the liquid has to be correspondingly high and that of the light very slow, Leonhard explains his experiments. It is like when a fish struggles against the suction of a waterfall: as long as the animal is faster than the flow of water, it can escape. But once the speed of the water exceeds the capabilities of the fish, it will inevitably fall over the waterfall. Since liquids cannot be accelerated to faster than light speeds, the researchers go the opposite way and simply slow down the light. For this purpose, strongly cooled steam from different atoms is irradiated with a first laser, which leads to a change of state of the steam. If a second laser beam is then passed through, this light moves very slowly, in the range of centimeters per second. If the steam is also accelerated to speeds above that of the laser beam, the whole thing is a light trap comparable to a black hole. (APA / red)