BIRTH OF BLACK HOLES

What are Black holes?  Where are Black holes?  How are they formed?
We all know Black holes are celestial bodies. The first thought occurring to most of us after hearing the word black hole is something “ huge”, “dangerous” and “difficult to explain”.Today, we shall try to unlock this celestial mystery in a simple way.

Ironically, to understand the functioning of the largest objects in the universe, we need to have a sound understanding about the working of its tiniest components.

ATOMS

Tiniest components of the universe are atoms and its subatomic particles. Atoms consist of protons, neutrons and electrons. This is what a conventional representation of an atom looks like.At the center of an atom is a nucleus which consists of protons and neutrons. Electrons revolve around the nucleus in different orbits. Protons and neutrons are 2000 times heavier than electrons.

Turns out , this simple representation of atom is not up to scale and hence it does not allow proper visualization. So how does an atom really look ?

As you can see, the nucleus is way too small and all the mass is concentrated at the nucleus because the electrons are too light.(Remember this point)

STARS

Stars, as we all know emit energy in the form of radiation. Where does this energy come from?

This energy is the output of reactions occurring inside stars. This reaction is nuclear fusion wherein, lighter nuclei fuse into heavier nuclei with the emission of energy. This energy radiates outwards whereas the gravitational force pulls the star inwards. The spherical shape of any star is the equilibrium position where the gravitational force cancels out the outward pressure due to nuclear fusion. With time, heavier elements formed due to nuclear fusion form the core of the star. As the star runs out of fuel, gravity can no longer hold the outer layers of lighter gases and they scatter in the space around (sometimes in a spectacular phenomenon called supernova).

From here, there are 3 possible outcomes.

1. White dwarf

2. Neutron star

3. Black hole

1   White dwarfs

As the fuel runs out, nuclear fusion stops and now the only force holding the core from collapsing under its on gravity is the electron degeneracy pressure. Now what really is electron degeneracy pressure. We all know that electrons revolve around the nucleus. In this context, gravitational force is trying to squeeze the electrons in the all the atoms. But, all electrons in an atom have individual identity (Pauli exclusion principle). They hate getting squeezed and being brought near each other. This creates a pressure and it is called electron degeneracy pressure. This state is possible only if the weight of the core is less than 1.4 times solar mass.

2.  Neutron Stars

If the mass of the core is greater than 1.4 times solar mass, then the electron degeneracy pressure can no longer hold the gravitational force which squeezes all the atoms.This forces the electrons in the core to fall into their respective nuclei wherein they fuse with protons to form neutrons.(see animation below). Now, this core consists only of neutrons. The neutron degeneracy pressure comes into effect here and it stops the core from collapsing further under its own gravity. The neutron degeneracy pressure, as the name suggests, is a phenomenon which occurs when neutrons are squeezed. This is quite similar to electron degeneracy pressure as explained above.

1.      Another important observation is, difference between the initial and final volumes in the above animation.
                                                    Density=Mass/Volume

      So,as volume decreases,density increases.This is exactly what is observed in a neutron star.A neutron star is so dense that a teaspoon of it would weigh a billion tonnes.

  

    Black holes

If the mass of the neutron star is more than 2-3 times solar mass, then even the neutron degeneracy pressure cannot withstand the immense gravitational force and the core collapses into a singularity (a point in space with infinite density.). The gravity around the singularity is enormous and it sucks in anything within its gravitational field of influence.There is a certain region around the singularity from where even light cannot escape. Since light does not come out of this region, we cannot see it. This region in space is called black hole.

The next obvious question is,"if we cannot see a black hole, then how do we know it is there?"

Scientists actually infer the presence of a black hole by observing the anomalous behaviors of other matter nearby.

Where are Black holes?
Black holes are found in the center of  most galaxies.Our galaxy,the milky way also has a super massive black hole at its center.

Are black holes dangerous?

Yes they are.Fortunately we do not have any black holes in the vicinity of our solar system.So we need not worry about getting sucked into some black hole.

Today, we tried to understand the birth of black holes.Many interesting phenomenon occur during the evolution of stars. Some of those include 'Red Super giants' , 'Supernovas', 'Pulsars' etc. But these phenomenon shall be discussed in detail some other time. That is all for now. Until next time. Adios!!