Why stars getting bigger, devouring planets and many other celestial objects that orbiting itself? And why collapses on itself after getting big
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There are two primary forces that govern almost everything about the start:
1. **Gravity.** Stars are massive objects that have a lot of gravity and this gravity wants to try and pull all of the star material into its middle.
2. **Fusion.** As the material gets compressed it heats up. When it heats up enough, it ignites nuclear fusion. This releases energy and creates a force that counteracts gravity.
The size of the star is determined by the balancing the inward pull of gravity by the outward push of nuclear fusion.
Stars start out as a cloud of dust. No fusion, all gravity. Gravity pulls it together and heats it up, when nuclear fusion starts (of hydrogen) it stops getting smaller.
When all of its fuel (hydrogen) is consumed, nuclear fusion stops so the only force left is gravity making it smaller again. It gets smaller and hotter until the next stage of nuclear fusion begins (helium).
Each successive stage of nuclear fusion creates *a lot* more energy than the previous, so the star is pushed out a lot larger than it was during the previous stage. This is why, when our sun consumes all of its hydrogen, it will get smaller and hotter until it starts fusing helium, and then balloon up, consuming Mercury, Venus, and most likely Earth.
This process repeats until one of several things happens:
* It reaches a point where there isn’t enough gravity to start the next phase of fusion, at which point the star shrinks as much as gravity will allow and then just cool down over billions of years.
* It continues over successive phases of fusion till it reaches iron which does not fuse. The gravitational force of such stars is so strong that it basically causes the star to explode in a super nova.
* If the core from a nova is massive enough, the gravity is so strong that it’ll squish the very atoms into pure neutrons and it’ll become a neutron star.
* If it is even more massive, it’ll continue collapsing until it becomes a black hole.
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