Black Holes

It took a long journey for scientists to prove that black holes exist. John Mitchell was the first person to come up with the idea that a black hole could exists in 1783, he developed the theory of black holes when he accepted Newton's theory that light consists of small material particles, called photons. He wondered how the movement of these light particles is impacted by the gravitational pull of the star they are escaping. He referred to them as "dark stars", however he doubted that such objects could exist and after publishing his information, he abandoned further research on the subject.

Mitchell’s research was further enhanced by Pierre Simon Laplace in 1795. Using Newton's Theory of gravity, Laplace calculated that if an object was compressed into a small enough radius, then the escape velocity of that object would be faster than the speed of light.

Then all this research took a turn of events as Einstein himself wrongly thought that black holes would not form, because he held that the angular momentum of collapsing particles would stabilize their motion at some radius. This led the general relativity community to dismiss all results to the contrary for many years, and black holes were considered nothing more than abstract mathematical concepts.

But in 1915, Einstein's theory of general relativity predicted the existence of black holes, which ended up proving his previous statement wrong. And then in 1967 John Wheeler, an American theoretical physicist, applied the term "black hole" to these collapsed objects.

Now I'll get to the point and explain how black holes are created. To keep it as simple and straightforward as possible, we can say that black holes are created when a massive star dies.But I would like to go into a bit more detail because a one line definition isn't enough!

A common type of black hole is produced by certain dying stars. A star which has a mass greater than approximately 20 times the mass of our Sun may produce a black hole at the end of its life.

In the normal life of a star there is a constant tug of war between gravity pulling in and pressure pushing out. Nuclear reactions in the core of the star produce enough energy and pressure to push outward. For most of a star’s life, gravity and pressure balance each other exactly, and so the star is stable. However, when a star runs out of nuclear fuel, gravity gets the upper hand and the material in the core is compressed even further. The bigger the core of the star causes the greater the force of gravity that compresses the material, making it collapse under its own weight.

For small stars, when the nuclear fuel is exhausted and there are no more nuclear reactions to fight gravity, the repulsive forces among electrons within the star eventually create enough pressure to halt further gravitational collapse. The star then cools and dies peacefully. This type of star is called a "white dwarf."

When a very massive star exhausts its nuclear fuel it explodes as a supernova. The outer parts of the star are expelled violently into space, while the core completely collapses under its own weight. If the core remaining after the supernova is very massive (more than 2.5 times the mass of the Sun), no known repulsive force inside a star can push back hard enough to prevent gravity from completely collapsing the core into a black hole.