Black holes continue to present a large number of mysteries despite decades of research that sought to uncover more details about them. We know a lot about them in the present, but there is more to learn.
Black holes tend to form when major stars run out of fuel. The sheer pull of its own gravity will force the star to collapse, leading to the formation of an object that is very dense and generates a gravitational pull that is so intense that nothing can escape it, even light.
Theorizing their existence
In 1783, an English natural philosopher called John Mitchell theorized the existence of objects which are so massive that even light is captured and retained. The modern perspective on black holes was pioneered by Albert Einstein in his seminal work, The General Theory of Relativity.
Einstein argued that gravity is responsible for the curvature of space-time. In the absence of gravity, an object would follow a straight line, but gravity forces it to follow a curved path. This approach was proved by Karl Schwarzschild, who managed to solve the equations created by Einstein and theorized the existence of the event horizon, the region of a black hole from which light cannot escape.
Learning about their formation
More than five years ago, Roger Penrose and Stephen Hawking proved that black holes are real, and they form in the aftermath of a process that takes place as a sequence of clear and predictable steps. Some stars are meant to become black holes from the start.
The term black hole was popularized by the Physicists John Wheeler in 1967. A milestone event was represented by the discovery of Cygnus X-1, the first stellar-mass black hole. In the following decades, new tools allowed researchers to discover the existence of supermassive black holes, and further advances could grant access to even more information in the future.