![]() In his earlier papers, Hawking had shown how relativity led to the singularity of a black hole, but then it was necessary to crack open the quantum chest to explain what was going on there.Īs Hawking would explain in the public version of his theory-formally incorrect for the sake of easier comprehension, as physicist Ethan Siegel explained-quantum theory suggests the continuous creation of virtual particle-antiparticle pairs that annihilate each other almost instantly. His genius was to combine two traditionally irreconcilable worlds, general relativity-the Einsteinian gravity used to explain the formation and evolution of black holes-and quantum mechanics, which describes the nature of the subatomic world. In 1974, a study by Hawking published in Nature shook the science of the time by proposing that black holes were not so black, nor did they grow endlessly as physicists, including himself, had previously assumed. The discoveries of Stephen Hawking shone light on the darkness of black holes, but at the same time raised questions. Thanks to this effect, the Event Horizon Telescope (EHT), an international collaboration of ground-based radio telescopes, succeeded on 10 April 2019 in providing humanity with the first image of a black hole, which occupies the centre of galaxy M87. Around that horizon the masses of dust and gas are so accelerated by the gigantic influx of gravity that they heat up and glow, emitting radiation and sometimes forming an accretion disc, which allows us to observe the shadow that the black hole itself casts on the luminous ring. Regardless of their size, they are all surrounded by an invisible boundary called the event horizon, the point of no return beyond which nothing can escape, not even light. ![]() At the other extreme, there are black holes even tinier than the stellar ones, micro-black holes formed in the early Universe. These are tiny compared to those that can store up to millions of solar masses, the supermassive ones that sit at the centre of many galaxies. These black holes are often called stellar black holes they originate after the death of a star whose internal gas pressure pushing outwards can no longer counteract the enormous force of gravity, which compresses its remaining matter until it collapses into a black hole a couple of dozen times the mass of the Sun. Lattice analogy of the deformation of spacetime caused by a planetary mass. Astrophysicists have been able to identify many such black holes by discovering cosmic objects orbiting around an apparent nothingness this gravitational pull reveals the presence of something that is otherwise completely invisible. Any object we place nearby will tend to fall towards the ball, so the gravitational effect of the black hole is felt in its surroundings. A black hole is a ball so heavy that it has at its centre a singularity, a region so infinitely dense that it collapses the bottomless trampoline. Space and time form a fabric that is curved by mass, like a trampoline. The existence of black holes stems from the theory of general relativity published by Albert Einstein in 1915, and the subsequent work of Robert Oppenheimer, Karl Schwarzschild, Subrahmanyan Chandrasekhar and others. It follows that we should have nothing to fear if the Sun were to be replaced by a black hole of the same mass-though our world would be much colder and darker, the planets would continue to orbit undisturbed because the mass of the black hole would be equivalent to that of the Sun. A black hole is not and does not create a vacuum, but quite the opposite it attracts through the effect of gravity, because the density of its mass is so enormous. ![]() In the mind of the public, black holes are often imagined as huge cosmic vacuum cleaners that suck up everything in their path, including light. The discoveries of Stephen Hawking (8 January 1942 – 14 April 2018) shone light on the darkness of these mysterious astronomical objects, but at the same time raised questions that will continue to trouble scientists for decades to come. His image has remained linked to the field that accounted for the bulk of his work-black holes. He was the last physicist whose unique profile transcended the boundaries of science to become, like Einstein, an icon of popular culture.
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