Black holes are among the most strange and mysterious objects in the Universe.These strange and mysterious objects are found in the center of almost all the Galaxies. Let's know about black holes in detail.
What Is A Black Hole?
A black hole is the remnant of an old star, which dies by collapsing on itself due to gravity.The main part of the black hole is its singularity. A black hole's all mass is concentrated in a single point in space with zero volume and has infinite density. This part of black hole is known as singularity. This make the black holes the objects with most extreme and immense gravity.
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| Artistic Illustration Of A Black Hole |
Event Horizon
If you look at the black hole, you will be seeing at the event horizon. Event horizon is the boundary of the black hole. Once you have crossed the event horizon, there is no way out. The gravity is so strong that even light can't escape from it. The closer you get to the event horizon, stronger the gravity becomes and ultimately, you reach at the event horizon from where you can't return. Falling through the event horizon is a bit like going through a water fall. The more you get closer the harder it is for you return back and when you reach at the edge, there is no chance of returning back.
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| The Boundary Where Black Part Starts Is Event Horizon |
Seeing A Black Hole
If we want to see a black hole, we will not be able to see it because it doesn't reflect any light. The light going in the black hole would be concentrated in its singularity. In other words, light can't escape from it's gravity, so we will see a black sphere reflecting nothing. You will see clouds of dust and plasma orbiting a black sphere. So it's not actually possible to see a black hole.
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| First Image Of A Black Hole |
Time Near Black Holes
The behavior of time near black holes is very interesting. Due to Einstein's theory of general relativity, we know that gravity affects time. The stronger the gravity of an object the more slowly time passes near it. Object with massive gravity can slow down time. Since, a black hole has most extreme gravity, time passes differently near a black hole. If you were able to board on a spaceship and go near a black hole time will pass slowly for you as compared to a person living on earth. If you orbit a black hole for an hour and then return back to earth there have been decades passed here on earth and there will be just an hour passed for you. If a person is observing you near a black hole from earth through a telescope, he will see you extremely slowed down. It is such an astonishing fact.
How Is Black Hole Formed?
To know about, how Black Holes are formed,
we have to know how stars die. Black Holes are formed when a huge star
collapses on itself due to its gravity. A star is primarily composed of
Hydrogen, which in its core is converted into Helium by the process of nuclear
fusion. In nuclear fusion, energy is released in the form of radiation, which
acts against gravity and prevents the star’s core from collapsing. In this way
stars are kept stable. As time progresses, due to the heat and pressure inside
a star’s core heavier elements like, Lithium, Neon, Oxygen and Silicon are
formed. But after some billion years, the star’s core starts producing Iron. A
star cannot create elements heavier than Iron. The fusion process that create
Iron does not generate enough energy. The star keeps on creating Iron until it
reaches a critical amount. At this point, the balance between the radiation and
energy is suddenly broken. Now, the core of the star collapses and within a
fraction of a second, it implodes while feeding more mass into the core. At
this very moment, all the heavier elements in the Universe are created and the
star dies in a Supernova explosion. This produces either a Neutron star or if
the star is massive enough, the entire mass of the core collapses into a Black
Hole.
Schwarzschild Radius
Any object could be formed into a black hole if it is compressed to the Schwarzschild radius. It was named after German physicist "Karl Schwarzschild", who found the solution to the Einstein's equations of a massive star. For example: if we compress an object equal to the size of our Sun to just 3 kilometres or an object equal to the size of earth to just 9 mm, it will become a black hole.
Death Of A Black Hole
As powerful black holes are they will eventually evaporate through a process called Hawking radiation. First it was believed that black holes will remain forever in the universe until the discovery of Hawking radiation by Stephen Hawking. Hawking radiation is a process through which black holes will evaporate. To understand this process, first of all we have to look at empty space. Empty space is not really empty but filled with virtual particles popping into existence and instantly annihilating each other. When this happens at the edge of a black hole near its event horizon, one of the virtual particles will be drawn into a black hole and the other escapes from it becoming a real particle. So the black hole is loosing energy. This happens slowly at first but becomes larger as black hole becomes smaller and smaller. For a black hole equal to the size of our Sun, it will approximately take 10^67 years to evaporate and if the black hole is bigger it will approximately take 10^100 years to evaporate. It is a very slow process and until the last black hole evaporates nobody will be around to witness it.
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