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| First photo of a black hole |
Einstein’s general theory of relativity allows for the existence of objects with infinite density (singularities). There are two types:
1.
Black holes,
accumulations of matter in a null volume, either at the center of a galaxy, or
as the result of a supernova explosion.
2.
The universe, at its initial moment (the Big
Bang).
A star like the sun is in equilibrium because the gravitational attraction, which tends to make it contract, is equal to the expansion caused by the nuclear reactions taking place inside the star. When a star much larger than the sun exhausts its nuclear fuel (first hydrogen, then helium, then other elements), as there are no longer nuclear reactions to stop the contraction, the star implodes. When the implosion rebounds, the star throws large quantities of matter into space: a supernova explosion, which for some time makes the star brighter than a whole galaxy. But there is always a remainder of matter, which gives rise to a new type of object.
