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.
There are two main forces that give a star its size – the atomic fusion that pushes out from the center, and gravity that pulls everything in towards the center. There are also two main parts of a star, the dense inner core (where the fusion happens) and the less dense upper layers
For most of a star’s life, atomic fusion happens at a relatively constant rate, so the size is pretty stable. But when it starts running out of hydrogen, the primary fuel for fusion, gravity starts winning and the core becomes compressed. The compression of the core generates heat (proportionally more than fusion, in which a lot of energy goes into light instead), which causes the upper layers to expand.
So this first stage of death causes it to get larger, but only in terms of diameter – it grows by becoming less dense.
Eventually, the dying core becomes so compressed and hot that the helium (output of hydrogen fusion) can itself undergo fusion, creating carbon. Eventually, the star burns through the helium as well and the now-mostly-carbon core starts to compress under its own gravity.
Here there’s a splitting point.
If a star has enough mass, there can be enough force from gravity to cause the carbon to fuse. There are a couple more cycles of fusion and gravity compression until the core is iron. Iron is a kind of stopping point – for any atom smaller than iron, fusion releases more energy than it consumes, allowing the reaction to be self-sustaining. But fusion of iron (and larger atoms) costs more energy than it releases. Once the core is mostly iron, there is a final gravity compression that becomes so dense that the structure of individual atoms collapses causing a supernova.
If a star doesn’t have enough mass at any of the gravity compression points to trigger the next round of fusion, the core slowly cools down and the upper layers float away and become a nebula
A star is essentially a very long lasting explosion in space, so they are experiencing 2 forces essentially – the outwards push of the explosion making the start want to “blow up” and an inwards pull due to gravity. Those two forces will form a balance that makes the star a certain size – the outer edge of the star is trying to “blow away” but getting pulled back towards the center of the start by gravity.
Forget the devouring stars and stuff part, that’s not really applicable here.
What happens is that as stars age, they are changing their fuel source and it’s a bit complicated because many different things *can happen*. Think of it this way, a star burning fuel is like 2 kids left alone in the kitchen. They’ll begin with the candy & chocolate, high energy “easy” food, then maybe they’ll switch to bread, still high energy but less desirable, then they start getting desperate and target the lesser foods, fruit, vegetables, etc. S*ometimes* something special happens, one kid is double checking the cabinets and drawers maybe discovers a hidden cookie or something during the fruits and veggie stage while the other is stuck eating radishes.
In the star once the “candy” is done, the star stars switching the “bread”, this is less energy for the star so the gravity part is still strong, but the outward explosion is less strong so the star starts to shrink. Since the color of the star is related to the energy it’ll also start changing colors as well. So the star (kid 1) is actually shrinking inside because it has less explosion, BUT then the outer part of the star (kid 2) discovers some cookies in some high up cabinets. It’s a bad metaphor I guess, but what is happening is the “inside” of the star is shrinking but the “outside” of the star eats the cookie and gets energy and starts expanding again. You get a funky star with a dense inner part (eating vegetables) but a really large and spread out outer part (that’s eating the cookie).
If the star didn’t have the cookie it just gets smaller and smaller (meaning denser) and becomes a dwarf. If the star has enough cookies it’s gets bigger and bigger and turns into a giant.
Eventually the cookies all get eaten too and the star has very little explosion left and the gravity pulls it back down inside. T[he result is basically like this experiment](https://www.youtube.com/watch?v=2UHS883_P60) the star collapses down super quickly and then blows back out super quickly. That’s a supernova.
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