due to the fantastic weather outside and the few discussions about stars and blackholes which appeared here (more or less serious topics) ive decided to get the ball rolling with a few more or less serious discussions about similar topics
I keep the explainations simple as not everybody here has deep knowledge about this stuff
-> the sun
what keeps it burning?
the sun emits light... so it produces actually a large amount of energy that is responsible for life on earth and many other processes in the sol system
the amount of energy is extremly high -> 4.000.000.000.000.000.000.000.000.000 watts (the largest powerplant on earth would need 25.000.000.000 years to produce that amount of energy).... oh and ehmm the sun its constantly producing that amount of energy
possible ways to create energy are:
- burning some matter
- chemical processes
- gravitational contraction
- direct matter to energy conversion
- fission
- fusion
1. burning matter was an imagination that started to appear centuries ago
we could imagine that the sun is filled with wood, coal, oil, whatever and burn it (of course assuming that it has the same mass as the sun)
the sun would burn... it would emit the same amount of energy... and in just about a few ten thousand years (depending on what you burn) the lights go off because there is nothing left to burn anymore
ok... thats not an option (afterall sun is burning for quiet a long time already)
2. chemical processes are a pretty ineffective way to create energy
some of you might remember time in school when you did experiments with different substances... you have put them together and depending on what you took you either got an endotherm or exotherm reaction
the most energy efficient creation is to combine 2 hydrogen atoms with one oxygen atm... result is some water and some energy
just like i said this reaction is the most energy efficient but still very very ineffective (thats why i use fuel for my car)
ok taking the mass of the sun and assuming that the sun would have enough oxygen then this chemical reaction would let the sun glow for about 18.000 years
throwing away this assumption and using the real about of oxygen that the sun hold we could expect that the lights go off in just 30 years
3. gravimetrical contraction is something cool
thats because you can see it on earth too... when you go down into coal mine you will notice that its getting warmer down there
gravity causes that more and more mass gets compressed... preassure raises and with the preassure the heat raises too
side effect of heat is light emission and there we have our energy again
it has to be said that the sun has a very high mass and therefore an extreme gravity so the conditions for such heating is actually good
The sun could shine for about 30 million years this way.... pretty good actually
but not good enough considering the age of the sun (4,6 billion years)
4. direct matter to energy conversion is the most effective way to create energy (and actually the most complicated and most unlikly)
here we have energy creation in its purest form with 100% efficiency
explained short: it would rip atoms apart and create pure energy
the sun could burn this way for 100.000.000.000.000 years (which is MUCH longer than the universe does exist)
problem is that protons (the atoms core) are extremly stable and i believe that there is no natural force in the universe (except the big bang) which is able to do that -> but i might be wrong here
5. Fission happens daily on our nuclear reactors here on earth
You shoot with a neutron on a heavy atom and split it. That causes an exothermic reaction which releases a large scale of energy.
Actually a pretty effective way creating energy but there is a problem... it requires heavy atoms.
The sun does mainly contain light atoms (hydrogen or helium). So such a reaction is very unlikly.
Calculations about how long the sun would burn if it would consist of heavy atoms are possible but highly depend on the kind of heavy atom (after all there are differences between uranium, plutonium or other heavy elements). So the results vary.
6. Fusion is cool coz its actually the opposite of Fission
With fusion we would merge light elements with each other to create heavier elements
e.g. take 2 hydrogen protons, create enormous preasure and heat (caused by gravity) and the final out come will be 1 helium atom (more or less)
thats how the sun does work
it fulfills the 2 neccessary conditions... 1. high gravity due to the high mass and 2. light elements such as hydrogen
but where does the energy come from?
while merging the hydrogen atoms loose mass (best description i can give when keeping it simple)
e.g.
mass of a hydrogen proton = 1
so the mass of 2 hydrogen protons (needed to create helium) = 2
but the mass of the created helium would only be 1.99 instead of 2 (just an example)
the missing 0.01 are energy
just to get the picture about which amounts we are talking:
around six hundred million tons of hydrogen are converted into 596 million tons of helium in the Sun every second (the difference in mass is the amount of energy created)
The sun has been burning this way for 4.6 billion years and will do the same for another 5 billion years with nearly the same rate of energy output
What happens when there is no hydrogen left anymore?
ok lets see what ive remembered over the years 
the fusion of hydrogen was the only reason why the sun did not collapse during the past billions of years because fusion causes a preasure inside the sun which is a force working opposite to the gravity which would normally compress the sun to a singularity (in case there wouldnt be other forces preventing that in the end)
ok fusion works opposite to gravity but fusion has stopped now coz there is no hydrogen... so gravity will work and the sun will shrink now
the cool "feature" of gravity is that it creates preasure and heat again once the mass is compact enough
a 2nd cycle of fusion will start as the sun got that incredible hot that now helium atoms will merge
theoretically this procedure happens over and over again until iron is getting created but every new stage of fusion creates less energy but requires more heat
our sun is too small to create even more heat and continue the fusion
iron btw. is the ultimate border of fusion as further merging requires more enery than it would produce (it would be an endotherm reaction)
at that point fission becomes more effective but that would require (as explained above) the existence of more heavy elements.
well i explained that now in the most simple way i could... i hope it was not too much (yet)
oh and we are talking here about facts and not about mysterious planets which pass our solar system every 3600 years
