Stars: The complete story

[Ganymede12]

I know the basics of star birth, life and death but there are many gaps/errors in my knowledge. I going to say what I know. Can you fill the gaps for me?

In a nebula, a disturbance, such as a supernova, will cause some areas of the nebula to become denser than others. Under the influence of gravity, the knots of dust and gas will contract and the pressure will heat the particles and trigger fusion.

Question: How does heat cause fusion to start?

Question: When and how does a proto star become a main sequence star?

Question: At this early stage, what causes stars to be different sizes and colours?

Slowly, over millions of years, the star will fuse elements, the fusion balances against gravity keeping the star stable. The fusion starts with Hydrogen and fusing up to Helium and continuing up to iron. As the stars move up the elements they change in size and colour.

When the star fuses the core to become denser and gravity over powers fusion so the core collapses and the star sheds its outer layers.

Question: Is a supernova just a violent dorm of the shedding of the stars outer layers?

Question: Are these outer layers still part of the star or are they already nebulae?

The dense core either Becomes a white dwarf or, if its large enough, a black hole.

Question: How does a white dwarf die? Does it just fade or does something else happen?

Question: How do Magnetars, Pulsars and brown dwarfs fit into the story?

Question: What is the difference between a Nova and a supernova in terms of how they are triggered?

So, where have I gone wrong, what have I missed and what are the answers to my questions?

Thanks in advanced!

[JulianO]

I know the basics of star birth, life and death but there are many gaps/errors in my knowledge. I going to say what I know. Can you fill the gaps for me?

In a nebula, a disturbance, such as a supernova, will cause some areas of the nebula to become denser than others. Under the influence of gravity, the knots of dust and gas will contract and the pressure will heat the particles and trigger fusion.

Question: How does heat cause fusion to start?

It makes the nuclei move faster, and if they are going fast enough they overcome the electrical repulsion, sufficient to get close enough for the strong and weak nuclear forces to do their stuff - which is about the width of a nucleus. The Jeans equation governs whether a cloud of gas will collapse or not - and exactly how it collapses and into how many stars is he subject of much simulation.

Question: When and how does a proto star become a main sequence star?

When it stars fusing hydrogen.

Question: At this early stage, what causes stars to be different sizes and colours?

Depends how much stuff collapsed to form the star. Bigger stars burn faster and hotter smaller ones slower. So generally its the size that gives the colour - but a secondary effect is what its made up of (metals in the lingo).

Slowly, over millions of years, the star will fuse elements, the fusion balances against gravity keeping the star stable. The fusion starts with Hydrogen and fusing up to Helium and continuing up to iron. As the stars move up the elements they change in size and colour.

When the star fuses the core to become denser and gravity over powers fusion so the core collapses and the star sheds its outer layers.

Question: Is a supernova just a violent dorm of the shedding of the stars outer layers?

No - its more related to the sudden collapse of the shell of stuff to the centre. Its not fully understood exactly how all the details work - but it seems to collapse into the centre and "bounce" out in an explosion.

Question: Are these outer layers still part of the star or are they already nebulae?

No - they're expelled as winds. With various speeds - for supernova nearly the speed of light.

The dense core either Becomes a white dwarf or, if its large enough, a black hole.

Question: How does a white dwarf die? Does it just fade or does something else happen?

Yes - in the words of the song, if fades away and radiates - eventually becoming a black dwarf - but it takes billions of years so none have done it yet. There is neutron star between the two too.

Question: How do Magnetars, Pulsars and brown dwarfs fit into the story?

Brown dwarfs are very tiny stars, barely fusing - a bit like very large Jupiters. Pulsars are neutron stars - remnants between white dwarfs and black holes. Magnetars are neutron stars with a very intense magnetic field.

Question: What is the difference between a Nova and a supernova in terms of how they are triggered?

A nova is a brightening of a star, generally just getting brighter but continuing to be a star. A supernova is the explosion of a star meaning its end.

So, where have I gone wrong, what have I missed and what are the answers to my questions?

Thanks in advanced!

Hope some of that helps

[Ganymede12]

Thanks a lot! That has cleared up lots!

It makes the nuclei move faster, and if they are going fast enough they overcome the electrical repulsion, sufficient to get close enough for the strong and weak nuclear forces to do their stuff - which is about the width of a nucleus. The Jeans equation governs whether a cloud of gas will collapse or not - and exactly how it collapses and into how many stars is he subject of much simulation.

I don't quite understand this bit though. What is "electrical repulsion"?

[JulianO]

I don't quite understand this bit though. What is "electrical repulsion"?

Fusion is the coming together of two hydrogen nuclei, or protons. Protons are positively charged, so everything else being equal they will try and move away from each other. It's like pushing two magnetic N poles together - they try and repel. So as a proton comes close to another one, their natural impulse is to avoid each other, as there is a repulsive force between them.

However like magnets, if you push them together hard enough, which in a star means racing towards each other so fast that the electrical repulsion is overcome, they can fuse. There is actually some quantum mechanics that helps the process along, or stars like our sun wouldn't shine at such low temperatures...

[Ganymede12]

Fusion is the coming together of two hydrogen nuclei, or protons. Protons are positively charged, so everything else being equal they will try and move away from each other. It's like pushing two magnetic N poles together - they try and repel. So as a proton comes close to another one, their natural impulse is to avoid each other, as there is a repulsive force between them.

However like magnets, if you push them together hard enough, which in a star means racing towards each other so fast that the electrical repulsion is overcome, they can fuse. There is actually some quantum mechanics that helps the process along, or stars like our sun wouldn't shine at such low temperatures...

Thank you once again! I thing I have most of the picture now, thanks for the knowledge!