Why do suns run out of fuel

[Malagabob333]

Am i right in thinking suns including ours are in fact nuclear fusion.If so why do they run out of fuel.Nuclear fusion in power stations produce more fuel in the process?So isnt it infinite.

[LazyGun]

It is a fusion reaction, corect.
No, it isn't infinite.
Essentially, the sun converts Hydrogen to Helium, giving off energy in the process.It does this at a rate of approx 5 million tons per second, and even taking that figure into consideration, it is estimated that the sun has a good few billion years to go yet.

[fo3nix]

There's no such thing as infinity.

Energy can never be created, nor destroyed. It has to come from somewhere, and it gets converted into something else.

After it's used up all its energy, it's dead.

[R1Geezer]

The nuclear power stations are fission not fusion, different ball game.

[jake-the-peg]

When you split certain heavy elements energy is released, this is called fission.

When you join certain light elements you get energy too this is fusion.

If you think about it you'll see that as we use heavier and heavier elements in fusion reaction we eventually get to a point where we cannot generate energy with fusion - the reaction is essentially endothermic.

You can see this energy in this graph

http://www.impcas.ac.cn/usr/wjx/zhonglz/jiangz uo/prc/binding.gif

at the top is Iron. this just so happens to be the cut off point.

When stars run out of hydrogen they start to use the helium that they have created etc. etc.

But when they get to Iron there's no more energy to be had. All the energy that kept those massive gravitational forces at bay is gone and the star collapses in on itself with such force that you get a supernova and every conceivable element is created.

With the exception of hydrogen, pretty much every element in your house, your computer, even in you was created in such a supernova