What is black hole:
Black holes are monsters in space. Simply, black hole is a massive concentration of matter. They are some kind of massive celestial objects and due to their special properties they are so unique in space. That means, no objects can replace a black hole. These are some places in this universe in where gravity is so strong that nothing can escape through it nor even light. This happens because, at a certain time (I will explain later) all matters are squeezed and collapsed to a certain point known as “Singularity“.
Types of black hole:
There are two types of black holes. one is Stellar mass black hole and the other is Supermassive black hole.
Stellar mass black hole:
Stellar mass black holes are those which are formed by collapsing massive or large stars during the end of their lives. When the fuels of stars are about to end, that means the nuclear fusion of the star is about to stop, then they cannot control their own gravity and collapse to a certain point. However, there is a theory about forming a black hole from a star which was proposed by Indian scientist Subrahmanyam Chandrasekhar. According to this theory,” A cold star of more than about one and a half times the mass of sun would not be able to support its own gravity.” In easy words, when a white dwarf dies at the end of its life, if its mass is greater than the limit then it will collapse itself and will form neutron star or black hole.
Supermassive black hole:
Supermassive black holes are those, which are formed in the center of a galaxy. In each and every galaxy, there is a supermassive black hole. Such types of black holes are formed by feeding different stars, galaxies and different gases present in the space. Our milky way galaxy also has a supermassive black in its center which name is “Sagittarius A*” and its weight is 4 million solar masses. That means, this supermassive black hole is almost equal to 4000000 suns. Our nearest supermassive black hole is “Andromeda” which weight is almost equal to 100 million solar masses, that is 100000000 suns. By observing these black holes’ positions, it was predicted that the two supermassive black holes will collide after some billion of years. That will cause the most powerful collision of black holes and create a new supermassive black hole.
What could become black holes:
Hypothetically, all objects could become black holes. That is, if we compress a large object to a certain point, its density will infinitely increase, so mass will also increase with the increase of density, but volume will decrease. this is a famous equation which is given as
where “ρ” is the density, “m” is the mass and “v” is the volume of that object. This equation clearly explains that density is directly proportional to the mass of the body. That is if, mass increases, then density also increases, but in this case volume decreases. That is why, when the volume of a large body decreases to almost zero, then density of the body becomes infinite.
ρ= ∞, when v→0
Hence, a black hole is formed. At zero volume, the object will be collapsed to a certain point which is called as “Singularity“. For example, if the Mount Everest is compressed to zero volume, it will become a black hole. Then it will suck everything near it. But, fortunately there is no way to compress the whole Mount Everest. But it can happen with the stars. Because, stars are too hot and they are the source of energy and they have larger “Schwarzschild Radius” ( The physical size of the black holes are measured with a special unit which is called Schwarzschild Radius) . After dying, they cannot hold their own gravity which results compression of the stars. At last they become black holes.
What will happen when we fall in a black hole:
After falling in a black hole we will be doomed. That means, we will lost in space.
There is a point which is known as “Event Horizon“. This is that point from where, after crossing this, no one can get back out. This is exactly like a “Waterfall“, in where after crossing a certain point no one can go back reverse. In case of black hole, this point is called “Event Horizon“. If you cross this point you will be thrown to nothingness. No one exactly knows where you will go. Maybe you will disappear forever by violating all laws of physics or you will appear in another universe or multiverse.
Near a black hole, the gravity is so strong that an observer will see something strange and unusual thing when you fall in a black hole. He would not see you directly suck into the black hole. Instead of this, he will see you approach the event horizon slowly. After reaching the event horizon, light coming from you will be increasingly “redshifted” until you disappear into nothingness. That means, he will never see you suck into the black hole, instead of this he will see you disappearing near the black hole. But at that point we will never be alive. Our body will be stretched infinitely and we will be looked like noodles. Scientists do not actually call it stretching, they call it “Spaghettification“. In this point our journey will be end.
Does a black hole affect time:
The gravitational field of every object warps space time. Space time is nothing but a 4th dimensional network of 3 dimensional space and an addition dimension called time. This space time warps with the mass of the body. That is, greater the mass of the body, warping will be more. That means, time depends on the mass of the body. According to the general theory of relativity, time slows down near gravitational field. In the closest area of the black hole, it warps space time such that time slows down here. That is why, black hole is considered as “natural time machine“. Because, if you are in a spaceship orbiting around the black hole, you will move slower in time compared to earth, which will result travel to future. So, the answer of the question is,”Yes. Black holes affect time.”
Is earth in danger range of black hole:
Even though a black hole can destroy everything in its path, but our earth is not in danger zone of any black hole. Our closest supermassive black hole is in the center of our galaxy which is too far away from us. So, we do not need to worry about it. We are in very safe range from any black hole.