'Wonders' question

[Robthevegetable]

One thing baffles me slightly. If a star is predominantly Hydrogen fusing into helium (until near the end of its life anyway), and then Helium into Carbon and Oxygen (because the Hydrogen fuel is spent) etc, etc. Then, the star eventually goes supernova and forms a nebula cloud of all the elements it produced during its life and death.

Now, if the star used all of its basic fuel (Hydrogen and Helium) during the 'first life', how can new stars form from the nebula cloud formed from the supernova? Although the cloud will have some Hydrogen present, how can there be enough to form new stars from the ashes of only a single star?

The good Prof. said that new stars will form from the nebula created from the supernova, but never went into any depth and I was wondering if anyone knows anything relating to this, or can point me in the right direction?

(Very long winded question... Sorry)

[Superewza]

I am also interested in the answer to this, and in the formation of nebulas such as Orion which form multiple stars - how can a nebula formed from the death of a single star create many, and while we're at it, how do they move away from each other? I don't suppose they stay relatively close to each other within the nebula.

[Robthevegetable]

I would've thought gravity will pull the multiple stars together when they form so close together... But then again I may be miles off!

[Nexus 6]

I think it may be that its a combination of the supernova and the ISM, the Interstellar Space Medium which is all the tiny particle's of gas and dust etc that are dispersed throughout the Universe

[Robthevegetable]

I did wonder that, but then I also wondered that surely the force of the supernova would expel almost all of the ISM (I had no idea that was what it was called) from the area the nebula would then inhabit.

[Stephen]

I've asked the Prof himself on Twitter to see if he will explain

Twitter

[Tim]

Great question

Just watched that episode, quite enjoyed it.

[Steve 1962]

I think the answer is that, because nuclear fusion only takes place in the core of a star (where the pressure and temperature are high enough) and very little fusion takes place in the outer layers of the star, there is still plenty of hydrogen left in the outer layers of the star when the core gives up the ghost.

This means that when the "smaller" star goes through its various red giant stages it blows off its outer layers of hydrogen into space and when larger stars go super nova all of the heavier elements enrich the hydrogen that's already been blown off.

I think this explains Brian Cox's point in episode 1 when he said that the age of the stars will evenually come to an end - i.e. all of the hydrogen floating around in the ISM is gradually used up by successive generations of stars.

....I think

Steve

[Nexus 6]

remember we are talking about things that may take billions of years to take shape but I know there are people on the forum with far better knowledge on such topics and hope one of them will give the correct details, my answer is just what I think may be how it works

[Superewza]

I think this explains Brian Cox's point in episode 1 when he said that the age of the stars will evenually come to an end - i.e. all of the hydrogen floating around in the ISM is gradually used up by successive generations of stars.

....I think

Steve

But if entropy says that complex things will inevitably become simpler things, then where does this fit in? Because hydrogen is the simplest atom going, and it will end up fusing into more complex atoms.

[Robthevegetable]

That makes sense as well... But, surely convection currents still exist in stars, meaning that the cooler surface layers will continually rotate with the hotter core (so as the hot material from the core comes to the surface (because heat rises), the cooler material near the surface replaces it), which should mean the use of Hydrogen in the star should be fairly extensive?

[Steve 1962]

But if entropy says that complex things will inevitably become simpler things, then where does this fit in? Because hydrogen is the simplest atom going, and it will end up fusing into more complex atoms.

The second law of thermodynamics doesn't state that complex things will inevitably become simple things - it states that ordered things will tend to become disordered. My understanding of this is that the initial uniform distribution of hydrogen in the universe immediately after the big bang (which had low entropy) has (and will continue to) become more "clumpy" and hydrogen will be gradually transformed into the 92 elements (i.e. it tends towards high entropy) in a progressively less and less organised pattern.

..I think (again)

Steve

[Steve 1962]

But, surely convection currents still exist in stars, meaning that the cooler surface layers will continually rotate with the hotter core (so as the hot material from the core comes to the surface (because heat rises), the cooler material near the surface replaces it), which should mean the use of Hydrogen in the star should be fairly extensive?

..getting out of my depth here.....I see what you're saying, but the heavier elements are formed in the deepest, hottest parts of the star, so wouldn't their increased density tend to damp down any tendency for them to convect upwards?

I tell you what I DO know - this is a heck of a lot more interesting than Gok Wan on TV!

Steve

[Robthevegetable]

Ah, I'd forgotten about that, but, then again, while the heavier elements in the core of the star may not convect upward, the heavier elements do not include Hydrogen...

Gok Who?

[Steve 1962]

but heavier elements are not Hydrogen...

So wouldn't the non fusing, cooler, lower pressure hydrogen "float" above the hotter, denser, fusing hydrogen / helium mix deeper down?

Steve

[Cunhaval]

Ah, I'd forgotten about that, but, then again, while the heavier elements in the core of the star may not convect upward, the heavier elements do not include Hydrogen...

Gok Who?

:D

[Robthevegetable]

Owwww, my brain!

[LukeSkywatcher]

I liked the pretty bubbles.

[zcapp96]

That makes sense as well... But, surely convection currents still exist in stars, meaning that the cooler surface layers will continually rotate with the hotter core (so as the hot material from the core comes to the surface (because heat rises), the cooler material near the surface replaces it), which should mean the use of Hydrogen in the star should be fairly extensive?

The analogy he used in the jail was a good one. Stars form layers and it is very difficult for material to transfer bewteen them. Hydrogen burning only (initially) takes place in the central one. Most of the star remains hydrogen and the outer layers will never become hot enough to start nuclear fusion.

Stars are incredably dense objects, it takes light 1000's of years to reach the surface so hydrogen atoms have no chance of migrating to the core!

[Nexus 6]

I tell you what I DO know - this is a heck of a lot more interesting than Gok Wan on TV!

Hi there is some good info here

Formation of the Universe

[Robthevegetable]

So wouldn't the non fusing, cooler, lower pressure hydrogen "float" above the hotter, denser, fusing hydrogen / helium mix deeper down?

Are we sure Prof. C isn't on this forum, I feel we need an expert!!

[Steve 1962]

:DYou started it!!!!

[Robthevegetable]

I like that I've got people thinking, although I think it's clear (without any disrespect) that none of us really know...

[LukeSkywatcher]

It's ALL very simple really.

You just need a degree in astrophysics.

[Nexus 6]

I like that I've got people thinking, although I think it's clear (without any disrespect) that none of us really know...

ye your probably right but thats what makes it all so interesting