What happens after a star die?

Hello everyone! Welcome back to AstroMe. In my previous post, we learned about the black hole and their formation. If you haven't checked it, click on this link- What is black hole and its formation

Did you know? There are certain conditions required for black hole formation. In this post, we will dive deep into this topic. C’mon, let’s jump into the black hole and know more!

In my previous post, we saw that a black hole is formed when a star dies. That is when a star runs out of fuel. So, what happens after the star dies?

When stars die, depending on their mass, they turn into one of the following:

·         Neutron star

·         White dwarf

·         Black hole 

            Ok! Now let’s see how this happens.

           

Fig 2.2

Subrahmanyan Chandrasekhar

In 1928, Subrahmanyan Chandrasekhar (Indian-American astrophysicist and Mathematician) researched what should be the mass of a star to withstand its own gravity after the fuels are used up.

He found that when a star contracts, the particles come closer and colloid with each other. When this happens, the particles tend to move in various velocities resulting in the expansion of the star. So for a star to remain constant there should be a balance between gravitational force and repulsion force.

Repulsion is nothing but a re­pul­sive force that even­tu­ally stops the atoms from get­ting together caused by the Pauli Exclusion Principle (states that two electrons in the same atom can have identical values).

 Subrahmanyan after long research found that when the star gets sufficiently dense, the repulsion caused by the exclusion principle is always less than the attraction of gravity in the star.

Take a look at the figure below, it depicts how the repulsion and gravitational force gets balanced.

Let’s see what is Chandrasekhar limit? Subrahmanyan calculated that a cold star of more than about one and a half times the mass of the sun would not be able to support itself against its own gravity this is known as the Chandrasekhar limit.

Depending on this limit, the stars turn themselves into white dwarfs or neutron stars, or black holes. Now let’s see what should be the Chandrasekhar limit for each category:

White dwarf

A star that has a mass less than   1.4 times the mass of the sun will turn into a white dwarf.

Characteristics of white dwarf:

·         low luminosity

·         Mass on the order of that of the Sun

·         Radius comparable to that of Earth.

 Sirius B is the first white dwarf discovered. It is part of the Sirius system it is also the brightest star in the night sky. There is a possibility of our sun also turning into a white dwarf. 

                         

Sirius B(Credit: NASA)

Neutron star

 If the star mass is exactly the Chandrasekhar limit it turns into a neutron star.

Characteristics of Neutron star:

·         high gravitational energy. Hence, very dangerous.

·         have a surface temperature of around 600000 K

·         it is  very hot & dense

Neutron star

Black hole:

If the star's mass is above the Chandrasekhar limit then that is when it turns into a black hole. 

For detailed information on black holes, check out What is black hole and its formation

Note: Mass of the sun is 1.989×10^30 kg.

Uff! I know that’s a lot to take in. But am pretty sure this information would have been mind-blowing to you. See you in my next post on another interesting space topic.