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How Does The Sun Burn Without Oxygen?
Does The Sun Really Burn?
The quick answer to this question is that no, the sun does not burn. At least not as we understand burning in our day to day lives. We are all familiar with fire and commonly use it for a variety of purposes, but no one on earth uses the type of "fire" that the sun uses to produce the light and heat we all depend on.
There is indeed a reaction taking place in the heart of our sun (and in all other stars as well) and it is one that produces vast amounts of heat and light but it is not fire. What we see and feel when we light a campfire or a gas range is a chemical reaction between oxygen and other chemical compounds or elements. The reaction going on in the sun is fusion - a nuclear reaction that we are only recently beginning to control.
What Is Fire?
This is a chemical reaction that uses the element oxygen to oxidize other elements. Most commonly we burn organic compounds, those that contain carbon, and the result is the production of carbon dioxide and water. In these cases the element oxygen has combined with the carbon and hydrogen in the compounds being burned to form the new compounds, but no new elements have been formed.
It is important to understand that the basic building blocks of the elements have remained unchanged, that although the combination of carbon and oxygen has produced carbon dioxide there is still both carbon and oxygen in that compound. The action of combing the two elements has released energy in the form of both light and heat, just as the sun does, but the elements remain intact and unchanged.
Such fire can burn slowly and evenly, as in the case of charcoal briquets, or rapidly and violently as in the case of dynamite or gasoline. However quickly it burns, though, it is still a chemical reaction and the energy released is quite limited as a result.
What Is Solar Fusion?
The sun "burns" with a fusion "fire", but what does that mean? We've already looked at the chemical reaction between oxygen and other elements or chemical compounds that produces light and heat, but fusion is much different.
Remember the alchemists of hundreds of years ago? Whose goal was to change common iron to gold? They had discovered basic chemistry, where one compound could be changed into another, but inside the individual elements nothing had changed. They still had the original elements, although the different combinations of elements produced different compounds. They needed a nuclear reaction, not a chemical one, to changed one element (iron) into another (gold).
The fusion that we see in our sun is the result of just such a nuclear reaction; four hydrogen atoms (an element) combining to form one helium atom (another basic element). There is no hydrogen left; no compound that still contains that element. It has all become helium through a nuclear reaction and the resulting energy release is huge when compared to a chemical fire. The actual process is more complicated, with several intermediate steps, but it comes down to the fact that hydrogen is changed into helium and lots of energy.
It is not easy to maintain this massive solar furnace, to keep it "burning". It requires incredible temperatures and pressures to convince hydrogen to fuse into helium; the sun accomplishes it through the sheer power of the gravity that its massive size produces.
Humanity has learned to produce a fusion reaction, but only an uncontrolled one in the form of a bomb - the hydrogen bomb uses fusion in the same basic manner that the sun does. One day we will perhaps learn to control the reaction used in the furnace of the universe - a lofty goal but one we could certainly profit from. Unlimited energy without pollution or waste products is something we very definitely need with our insatiable appetite for more and more energy.
The sun is composed primarily of hydrogen and the fusion product of helium, but consumes some 600 million tons of hydrogen each second. This consumption of 600 million tons produces only 596 tons of helium; the leftover 4 million tons of mass shows up as energy just as Einstein predicted with his famous formula of E=MC^2. Energy = mass times the speed of light squared; that's a lot of energy when 4 million tons are converted each second!
One day the sun will run out of hydrogen, but even that will not stop the fusion reaction; it is possible to fuse heavier elements, including helium, into ever heavier and heavier elements. The end is reached only when the suns core is turned into carbon - as carbon cannot be compressed further fusion will stop. When that time comes our sun will die, slowly cool and the solar system will go cold forever, but the process of a star dying is long and drawn out and won't even begin for another 5 billion years.
So, you see, there is really no mystery as to how the sun can burn without oxygen because it doesn't really "burn" at all. What we call "fire" in the sun is, instead, a very powerful and complex nuclear reaction that has nothing to do with oxygen or even the chemical reaction we term "burning".
© 2012 Dan Harmon