{"id":250643,"date":"2017-12-19T18:10:31","date_gmt":"2017-12-19T20:10:31","guid":{"rendered":"http:\/\/revistapesquisa.fapesp.br\/?p=250643\/"},"modified":"2018-03-28T17:09:49","modified_gmt":"2018-03-28T20:09:49","slug":"astrophysics-in-the-bathtub","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/astrophysics-in-the-bathtub\/","title":{"rendered":"Astrophysics in the bathtub"},"content":{"rendered":"
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Silke Weinfurtner \/ Nottingham University<\/span><\/a> Vortex produced by the drain in the center of the tank, during the experiment that detected superradianceSilke Weinfurtner \/ Nottingham University<\/span><\/p><\/div>\n

Waves that propagate on the surface of water become a little higher as they cross the region surrounding a whirlpool created by the open drain of a tank. Their size is amplified because they receive some of the rotational energy from the whirlpool, an effect called superradiance. The existence of this effect was first confirmed in an experiment conducted in 2016 by an international group of researchers led by German physicist Silke Weinfurtner of the University of Nottingham in the United Kingdom. In her laboratory, Silke and her colleagues\u2014among them Brazilian physicist Maur\u00edcio Richartz\u2014produced this phenomenon using a glass tank and water containing a green fluorescent dye. The test was filmed with a 3D camera, which allowed the researchers to detect the increase in the height of the waves caused by superradiance. The effect is small, but it attracted the attention of the physicists because it simulates what is thought to occur with light near a rotating black hole. These results are described in an article published on June 12, 2017 in the journal Nature Physics<\/em>.<\/p>\n

“The theory behind superradiance is very well known, but no one had observed the phenomenon experimentally,” says Richartz, a professor at the Federal University of the ABC. He helped plan and carry out the experiment and says that, under the conditions in which the test was conducted, waves on the surface of the water can be described by equations of motion almost identical to those of light waves propagating near a black hole. As the equations are practically the same, the confirmation that superradiance occurs in waves formed in water represents the first concrete evidence that this phenomenon, although difficult to detect, must exist in the vicinity of black holes, as predicted by the theory. Until recently, theoretical studies have suggested that black-hole superradiance would cause a magnification of electromagnetic and gravitational waves too small to be observed by astronomers. In an article published this year in the journal Physical Review D<\/em>, physicist Jo\u00e3o Rosa, of the University of Aveiro, Portugal, suggests that superradiance could be amplified in the vicinity of pairs of black holes and neutron stars. Signs of the phenomenon could then be detectable by the Square Kilometer Array (SKA) radio telescope, whose antennas will be installed in South Africa and Australia, and by the Interferometric Gravitational Wave Observatory (LIGO) in the United States.<\/p>\n