Elementary Particles under the Lens of the Black Holes

where M is the black hole mass. Notwithstanding it took many decades before the scientific community accepted that black holes were physical solutions which could be indeed realized in nature. In 1939 we can still find A. Einstein stating in the conclusions of an article [1]: “the Schwarzschild singularities do not exist in the physical reality”. This was not what J. Oppenheimer and his student, H. Snyder, concluded in the same year [2], however, after analyzing the collapse of massive stars. In 1938, J. Oppenheimer and G. Volkoff found that neutron stars had a limit for its mass beyond which they should collapse [3]. In the year after, Oppenheimer and Snyder decided to analyze it in more detail. For technical reasons, they assumed some simplifications: spherical symmetry, constant density, no rotation and no shock waves with emission of matter or radiation. Under these conditions they concluded that the collapse would lead eventually to a black hole indeed, but there remained some unclear features to be understood. In contrast to the description made by observers at rest on the surface of the star who would witness a continuous collapse towards the singularity, asymptotic observers would see the star surface like “frozen” on the event horizon. These seemingly contradictory descriptions were only reconciled after D. Finkelstein found in 1958 a coordinate system which was able to cover smoothly the internal and external regions of the black hole [4]. This conceptual step in addition with more precise numerical simulations, which were possible thanks to a better comprehension of the nuclear structure, ended up to corroborate Oppenheimer and Snyder’s conclusion and bit most skepticism about the possible existence of black holes. J. Wheeler, in particular, evolved from criticizer to supporter of the black hole idea and in 1967 he introduced the denomination black hole to what was called collapsed star in the west and frozen star in the east. More than 40 years after the Schwarzschild solution was discovered, black holes were treated at least as a real possibility.