Black Hole, Event Horizon, and Singularity.

What is Black Hole?

Black Hole is formed when an extremely massive star collapses under the force of gravity. Gravitational force is so strong near a black hole that even light cannot come out of it. Black Hole is invisible because no light gets out of it which is quite amazing. Black Holes were predicted by Einstein’s Theory of General Relativity. When a star dies, all of its stuff concentrates to a small space. If there is no light emitting out of the black hole, then how can it be observed. Scientists are quite intelligent. They always search a way, and when there is no way, they make a new one.

How are Black Holes formed?

The survival of a star depends on the balance between gravitational pull and
nuclear explosions. Force of gravity pulls the matter of a star inside while
explosions pushes it outward. When a massive star runs out of fuel, there is an
imbalance created between the two forces. Gravitational pull attracts all the
stuff of a star to a smaller and smaller space which results in the formation
of a black hole
.

Singularity in a nutshell

American Physicist Kip Thorne describes singularity as “The point where all laws of physics break down”.

Gravitational singularity is a one-dimensional point at the center of a black hole where huge mass is concentrated in a very small space. Gravity and density become infinite which causes a rupture in the fabric of space-time. Even the General Theory of Relativity breaks down at this point. If an object enters into a black hole and approached singularity, it would be stretched and squeezed like spaghetti due to a large difference in the force of gravity on different parts. This hypothetical process is named “spaghettification” which is quite funny. General Theory of relativity has many implications. Suppose there are two persons. One of them is a safe and sound observer while the other one is trying to sacrifice his life for the sake of science. Now when the person getting nearer and nearer to the black hole, the observer would see the person slows down till it reaches the event horizon where everything stops and would never fall to a black hole.

What is an Event Horizon

The event horizon is the edge or a boundary of a black hole which is related to the object’s escape velocity. Now escape velocity is that velocity required to escape or get out of a planet’s or star’s gravitational field. A gravitational field is a space where the force of gravity attracts everything under its influence. When an object approaches a black hole, more and more velocity is required to escape its gravity. Event Horizon is a limit or a threshold for escape velocity. If an object is on the outer side of the event horizon, escape velocity is less than the speed of light but unfortunately, if an object crossing it, it would need velocity more than the speed of light which is impossible. That object would be lost forever. Avi Loeb of Harvard University says that “The event horizon is the prison wall — one can get in but never get out.”

Size and Density of a Black Hole

Blackhole can be small as well as large. The smallest black hole can be the size of an atom and it is believed that these kinds of black holes formed at the time of big bang when the universe came into being. A large black hole can have any size. If there is a black hole having a mass equal to the sun, its diameter would be 6 kilometers or 3.7 miles. The largest black holes are called supermassive black holes. It is believed that every galaxy is having a supermassive black hole at their center around which all the planets and stars are revolving. “Sagittarius A*” is the supermassive black hole in our galaxy called Milky Way.

Density is defined as mass divided by volume. In a black hole, there is huge mass concentrated in extremely small space so density approaches infinity.

Can We See a Black Hole

No, we cannot see a black hole because no light can get out of it. A black hole is invisible. From outside, we can only observe the mass, charge and angular momentum of a black hole. These three properties completely describe a black hole.

What Happens if a Person Enters a Black Hole?

When someone gets to know about a black hole and its weird properties, a natural question pops up in mind and that is, what would happen to a person or an object if it enters into a black hole. This question can be answered using an optimistic and pessimistic approach.

Using the pessimistic approach, the gravitational field near the black hole is tremendously large. When a person crosses the event horizon, there are no possibilities for the person to come back. A black hole stretch squeezes and eventually destroys everything approaching its center or singularity which is quite terrifying. The possibility of this event makes the black hole a nightmare for the astronomers and space explorers.

Science fiction and movies mostly portray an optimistic approach. A black hole can be a potential gateway to new dimensions that we do not know. Different thought experiments are carried out clarifying misconceptions regarding black holes. Black holes can make hyperspace travel possible. Hyperspace is an extradimensional space in which a person can travel faster than real space. All these are seemingly science fiction concepts but we should not forget what the great Physicist and Cosmologist Stephen Hawking said: “Today’s science fictions are tomorrow’s science facts.” We must hope for a better future.