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Image source, POT
Visualization of a black hole made by NASA.
Although his own theories suggested their existence, even Albert Einstein himself thought that, in practice, they would be difficult to find.
Black holes, those centers of extreme gravity deep in the cosmos, have for years been one of the subjects that has generated the most headaches and uncertainties among astronomers.
This Tuesday, the Royal Academy of Sciences of Sweden decided to recognize through three authorities on the subject those who over the years have dedicated themselves to studying these strange entities that escape even the imagination.
British Roger Penrose, German Reinhard Genzel and American Andrea Ghez will be awarded the Nobel Prize in Physics in December for their findings on black holes.
Image source, fake images
The Nobel Prize in Physics was awarded to three scientists who have studied black holes.
“In the case of Genzel and Ghez, their contributions are that they managed to demonstrate through astronomical observations the existence of a supermassive black hole in the center of our galaxy,” he explains to BBC Mundo Eduard Larrañaga, theoretical physicist and professor at the National Observatory of Colombia.
“In the case of Penrose, although we understand that the Academy also awards him for the issue of black holes, his contribution to physics goes much further,” he adds.
According to the Colombian physicist, it was Penrose’s equations and theories that helped scientists more than half a century ago to understand that the black holes that Einstein’s theory of general relativity had foreseen were actually possible.
“Although the theory of general relativity dates back to 1916, until the 1950s the subject was not addressed much, because even Einstein himself thought that black holes were not going to be possible in nature because of their strange characteristics,” he recalls .
The Colombian physicist says that in the 1950s, some Einstein students began to do some calculations to explain how a star, when it died, could give rise to a black hole.
“However, the calculations that were made at that time were made assuming that the star was completely spherical, but it is an idealization of the problem, because in reality the stars are not like that,” says Larrañaga.
“What Penrose does is show that even stars that did not have a totally spherical behavior, but had perturbations, could undergo a collapse process that would lead to the formation of a black hole,” he adds.
Thus, he says, Penrose’s theory proved the possibility of the existence in nature of these elusive objects.
From left right: Roger Penrose, Reinhard Genzel, and Andrea Ghez.
According to the Colombian academic, Penrose also contributed to physics with notable developments on gravitation or cosmology, but his contribution to the study of black holes did not determine their origin.
The now British Nobel Prize winner considered that in some points of the universe and, especially in the center of black holes, there were certain “singularities” that, in some way, questioned all the laws of physics.
Years later, his theorem on singularities would be applied by his disciple, Stephen Hawking, to also understand the primeval moment of the Big Bang.
Singularity
According to Larrañaga, Penrose started from the understanding that there are certain points, or conditions of space-time, where physics stops working.
That is, where the laws that we believe to be universal do not apply.
“For example, a black hole. You know that a black hole is an object with enormous gravity. Why does it have enormous gravity? Because it has a lot of mass. And it turns out that this mass is concentrated in a very small region. All that. mass went to a point. So at that point gravity is infinite, density is infinite and many other physical quantities go to infinity, “he explains.
Image source, fake images
Black holes have such great gravity that they don’t even let light escape.
According to the scientist, when this happens, those “infinities” cannot be handled with the usual mathematics: “Any equation with infinities stops making sense,” he says.
This, he says, gives rise to these “singularities” in space-time.
“It is the point in the universe where the equations of physics stop working, for some reason. Usually it is because physical quantities like mass or density grow, they go towards infinity,” he says.
This is what happens, says the scientist, in the center of black holes.
There “all the mass is accumulated, so the density is infinite. At that point, the equations of the physics of general relativity do not work,” he points out.
According to Larrañaga, the singularity is then that central point of black holes where all the mass is concentrated.
“It is the heart, the core of the black hole, where the density is infinite and for that reason, the equations of physics do not work, because where the density appears, everything grows. Then the equations stop working,” he argues.
Image source, fake images
The researchers believe that only the direct collapse of matter can explain such large massive holes.
The Colombian physicist recalls that this approach was fundamental, because it helped to understand both black holes and cosmological processes such as the big Bang.
However, he explains that its complexity and what it implies for physics are such that many scientists question its existence.
“There are many physicists today who believe that singularities do not exist, because if we accept them, the laws of physics collapse there,” he says.
“So when we as physicists accept singularities we are accepting that physics has a limit“.
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