Stars - Summary from the part of a Nebula to becoming a Main Sequence Star

So far we have discussed the following about the life span of stars.

1. All stars start their life at some part of a nebula (a nebula is a giant cloud of gases and dust particles, it can be as big as trillion Suns).

A Nebula

2.  This part of the nebula starts to collapse towards a central point due to the gravity. 
3. Once the particles start to rush towards the central core they collide with each other more often (which is known as increase in collision frequency). 
4. Due to increased collision frequency this mass starts to heat up and towards the core there is higher collision frequency so does higher temperatures at the core. 
5. Also due to higher collision frequency higher heat is generated, as a result the mass starts to spin faster which is known as angular momentum. 
6. Gravity still winning against two forces working against it; first the thermal (heat) energy created due to the collisions, push outwards and second the angular momentum of the whole mass (spinning) tends to push outward. At this stage the spinning disc of mass is known as a Proto Star. 

A Proto Star

7. Gravity still pushing the whole mass inwards until the core got so hot and the atoms are so dense at the core that Nuclear Fusion of the Hydrogen Gas Starts. Huge huge energy is released as a result and this energy also works against the gravity. Energy from the fusion is so tremendous that it balance out the contracting Gravitational force. As a result star stops contracting any further. It is called the equilibrium phase and the star is known as main sequence star. 
8. Brown Dwarfs: These very low mass proto-stars which are not large enough to start the hydrogen fusion so never become a shining star in equilibrium phase. Brown dwarfs are not big enough to become a star and not small enough to become a planet. 

A Brown Dwarf

A star which enters the equilibrium phase is known as the Main Sequence Phase. As soon as the fusion starts to take over the gravity that creates a shortage of hydrogen atoms as a result the fusion energy comes down to equilibrium. As soon as Gravity starts to take over, there are more collisions and more hydrogen atoms at the centre as a result more energy is generated from fusion and higher gravity is stabilized towards equilibrium. What an Automatic Thermostat?    

Equilibrium phase is the young age of the star. Our Sun is in equilibrium phase right now.   

The next question is, how long a star stays in the equilibrium phase? 

It all depends upon the initial mass of the star which started to collapse. For a larger mass, once the fusion starts it burns out it’s fuel (the hydrogen gas) very fast and have a shorter life span. The low mass stars have the longest life spans as they burn hydrogen at a very slow rate. 

Next post we will discuss what happens to the stars once all the hydrogen in it burned out? What will happen to The Sun once all its hydrogen will be used up?

Following are the links to my previous posts on The Story of a Star

https://steemit.com/science/@mathworksheets/story-of-a-star-in-the-womb-of-a-nebula

https://steemit.com/science/@mathworksheets/a-star-story-forming-the-protostar

https://steemit.com/science/@mathworksheets/story-of-a-star-a-brown-dwarf

 The story of a star still continues.......