How Are Black Holes Created

As stars fascinate everyone. However, without a doubt the most fascinating thing about them has to be black holes. Black holes have become such a staple in astronomy today that even people who don’t know anything about space know about black holes. What exactly are black holes? How do they come to be? In simple terms, it is a star so massive that not even light can escape its gravity.

How a Star Becomes a Black Hole

Stars have life cycles. Depending on their starting mass, they could go two separate paths. However, the starting point of both paths begins with a massive accumulation of gas clouds. These gas clouds contain over 98% helium and hydrogen. The elements in gas clouds begin to gather together.

This starts a domino effect where the larger it becomes the more gas it will gather to itself. Soon, the gas cloud becomes so massive the gravity at its core becomes ever increasing. The force of gravity soon becomes so great that the atoms colliding with each other begin to cling to one another. Light elements change into heavier elements.  This is called nuclear fusion and it marks birth of a star.  The star will spend the majority of its life in this stage which is called the main sequence.

A typical life cycle of a star showing how stars can turn into black holes

Nuclear fusion can continue for millions of years inside a star.  Eventually, though, the amount of light elements such as hydrogen begins to fade.

Heavier elements such as iron start to appear. The star begins to expand. It begins to swell to over double its original size. It the star’s original mass isn’t that much relatively, it will become a red giant.

However, if the mass is great enough, it will become something called a super-giant. It will then spend approximately 10% of its life in this stage.

The star stays stable for a few more millions of years until the force of the gravity can no longer hold the star together. Eventually, the star dies. As the star dies, it explodes sending a burst of its outer layers. It is here that it becomes a planetary nebula. If the star is light, the star’s core will stay intact leaving it to being something called a white dwarf.  The white dwarf is mostly composed of carbon and oxygen.  The surface is still hot. As it cools, though, it becomes a theoretical black dwarf.

Something special happens when the star has a large amount of mass. As the star explodes due to its inability to stay stable, it becomes a supernova. As the star tries to explode, gravity forces all the elements trying to escape back in. The force of the gravity is so strong that not even light can escape it. This is the birth of a black hole.

The Theoretical Discovery of a Black Hole

While it was only recently that we actually discovered proof of black holes, the theory and thoughts for it existed as far back as 1783. John Michell, born 1724, was an English clergyman who was the first to be recognized as publishing the theorized existence of black holes. He wrote a letter Henry Cavendish of the Royal Society describing them. In it, he supposed that a star 500 times ours would collapse at such a rate the nothing could escape its gravity. Black holes would also go on to be described in the 1796 book “Exposition du systeme du Monde” written by Pierre-Simon LaPlace.  However, the subject wouldn’t be covered again until years later. The problem was that scientists couldn’t figure why sunlight, a weightless wave, could be affected by gravity.

In 1915, Einstein solved this problem with general relativity. He showed and proved that light could be affected by gravity. The proof came when a solar eclipse allowed scientists to visibly see the gravity of the sun changing the observed position of a star in 1919. Having proved that light can be affected by gravity; black holes had a more solid foundation on the road to discovery.

Black hole Swift J1644+57 discovered in May 2011. You can read more about this black hole here

Since 1916, the theory of black holes evolved. During that same year, Karl Schwarzschild applied Einstein’s theory of relativity to characterize a black hole. In his work, he described a radius of a sphere called a Schwarzschild radius. If all the mass were to be compressed within that sphere, the velocity needed to leave the gravity of that sphere would equal the speed of light.  In simpler terms, he described the size needed for a sun to collapse into for it to become a black hole.

A still larger problem existed. How could you find a black hole?  After all, if not even light could escape its gravity, you couldn’t just find it in a telescope. There had to be other ways to prove that it existed by actually finding one. It wasn’t until a man named Stephen Hawking came along and showed how you could find a black hole with something called Hawking radiation.

It was theorized that black holes had something called an event horizon. This would essentially be the point in which would separate the material that went into the black hole and material that didn’t. It was already shown how particles appear into existence. These particles split into a particle and anti-particle. If this happens at the edge of the event horizon, then one particle would fall into the black hole and the other would be thrown out into space. By looking for this radiation, you could find the existence of black holes.  In 1970, scientists found an object in space that couldn’t be detected with light but was found to be emitting x-rays.  It was large enough that it was found to have a body orbiting around it. However, it had a mass larger than that of a neutron star. In 1994, it was shown how black holes were found to be at the center of some galaxies by the Hubble Telescope. Hubble had shown that there were large objects with large amounts of mass orbiting the center.

Until next time!

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