[ukmicky (OP)]

why does the fusion process in the sun continue for billions of years. why doesnt it just blow up in one big bang  

why isn't all the hydrogen accessible all at once

Michael

[Hadrian]

Is not the Sun is still in a process of nuclear fusion right now and that is why it hasn't exploded?




What you do speaks so loudly that I cannot hear what you say.

[ukmicky (OP)]

Yes it been an ongoing process for the last 4.5 billion or so years but why dosent  all the hydrogen get coverted  in to helium at the same time in one go. what holds back some of the hydrogen for later conversion why cant it all be converted together.

Is it because the fusion process only happens in a tiny area of the sun and the rest of the sun is just like a giant fuel tank full of hydrogen fuel waiting to be drawn in.
Only i would have thought a large proportion of the sun would be hot enough and be under enough presure for fusion to occur making the remainder containing future fuel small, if you get what i mean .

Michael

[another_someone]

OK, I will make a wild guess about this.

The only way that the sun can release energy is by radiation (and some cooling by the solar wind, and maybe neutrino radiation, carrying away energy).

Since most of the energy (the solar wind, and radiation) can only escape from the surface of the sun, thus most of the energy remains trapped deep within the Sun.

Since the energy remains trapped, it can power the endothermic reaction that reverses the fusion of hydrogen to helium – i.e. hydrogen fuses to make helium and releases energy, but this is counterbalanced by energy used to tear the helium apart into hydrogen again (i.,e. raw protons); and it is only where the energy can escape (i.e. near the surface) that the reaction cannot be reversed.

George

[neilep]

Doesn't it take many thousands of years for the radiation to finally escape from the Sun ?..It does, doesn't it ?

Men are the same as women, just inside out !

[Soul Surfer]

What happens is, as stars like the sun are forming they contract and heat up by simple adiabatic compression (just the same reason that awhen you compress the gas in your bicycle pump it gets hot.  The hottest part is right in the centre so that is where the energy generation starts under very high pressure and temperature.  The release of energy increases the temperature and hence the pressure causing the core to expand a bit and cool down so the reaction slows down.  This negative feedback process stabilises the reaction and stars remain very stable for quite a long time although the do tent to get slowly a bit brighter eventually when the core has ee substantially depeleted of hydrogen the process goes on the surface of a core of hot helium whigh starts to work its way outwards this eventually causes the reaction to speed up and the star gets brighter but funnily enough it doesn't get hotter it just gets bigger and cooler.

This java applet helps to show this

http://instruct1.cit.cornell.edu/courses/astro101/java/evolve/evolve.htm


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