A black hole is an astronomical object so densely massive that anything falling into it, including light, cannot escape its gravity.
Karl Schwarzschild
Proved the existence of black holes by solving Einstein's equation
https://ru.wikipedia.org/wiki/%D0%A7%D1%91%D1%80%D0%BD%D0%B0%D1%8F_%D0%B4%D1%8B%D1%80%D0%B0#:~:text=%D0%98%D0%B7%D0%BE%D0%B1%D1%80%D0%B5%D1%82%D0%B0%D1%82%D0%B5%D0%BB%D1%8C%20%D1%82%D0%B5%D1%80%D0%BC%D0%B8%D0%BD%D0%B0%20%D0%B4%D0%BE%D1%81%D1%82%D0%BE%D0%B2%D0%B5%D1%80%D0%BD%D0%BE%20%D0%BD%D0%B5%D0%B8%D0%B7%D0%B2%D0%B5%D1%81%D1%82%D0%B5%D0%BD%2C%20%D0%BD%D0%BE,%D0%B8%D0%B7%D0%B2%D0%B5%D1%81%D1%82%D0%BD%D0%BE%D0%B5%20%D0%B8%20%D0%BD%D0%B5%D0%B8%D0%B7%D0%B2%D0%B5%D1%81%D1%82%D0%BD%D0%BE%D0%B5%C2%BB%20(%D0%B0%D0%BD%D0%B3%D0%BB.