British scientists have recreated the conditions of a black hole using a giant bathtub and water dye

Scientists are unlocking the mysteries of black holes... in a giant bath tub at the University of Nottingham. A team from the Quantum Gravity Laboratory says they have successfully simulated the conditions around black holes and published the first statistical evidence of an effect known as super-radiance, whereby a wave hitting a rotating black hole can extract energy from it.

They built a specially designed 3 metre by 1.5 metre tub with a hole in the centre. Two thousand litres of water is pumped in a closed circuit to establish a spiralling draining flow, just like in a normal bathtub when the plug is removed. Small waves were then generated at varied frequencies to simulate the enigmatic ripples in space.

"Although we don't have a black hole, the surface waves behave as if there were a black hole in the system," explained researcher Sam Patrick. "That's enough to give rise to these interesting effects and we can then study these effects. So although we don't have a black hole we still get the same effects that occur around black holes."

Black holes are regions so dense with matter that the pulling force of gravity is so strong that not even photons of light can escape their gravitational pull. A black hole's gravitational point of no return is known as the event horizon. Studying them has largely been confined to the realm of theoretical physics.

Led by Dr. Silke Weinfurtner from the School of Mathematical Sciences, their primary experiment is based on the super-radiance theory: that any waves that enter the area just outside - but don't pass - the event horizon will be dragged round by the rotation and emerge the other side with more energy. In effect, extracting energy from the black hole and thus diminishing the black hole's pull.

Once the super-radiant scattering effect is created, a specially designed 3D air fluid interface sensor captures the data.

"A projector in the middle projects a pattern on the water. And then we have two cameras on the side that record this pattern," said researcher Théo Torres. "And by looking at this object from two different angles, exactly like our eyes, we can see in three dimensions."

Torres added that they observed how the wave pattern changed once it had passed the 'black hole' vortex in their system. "Basically it says that something happened. And then by analysing more carefully this scattering pattern we can see if the wave has extracted some energy from the vortex. So, basically the idea is that the wave after the vortex has more energy than the wave before," said Torres.

The team says this 'super-radiance' phenomenon has never been observed before.

"We showed that super-radiance does exist in our vortex flow. This was quite a big result for us because super-radiance is an effect that's been known about since around the 1970s but no one had ever actually demonstrated that it exists in these rotational systems from an experimental point of view," added Patrick.

The research, published in the journal Nature Physics, could lead to similar experiments that demonstrate black hole theories in a laboratory setting that had previously only been hypothesised.

Produced by Jasper Pickering. Special thanks to Leon Siciliano.

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