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If you look at images of the sun, it really does look like it is on fire: a giant burning ball that lights up the sky and space around it. However, on Earth, we do know that you need oxygen to create and maintain fire, but space is a vacuum that does not have that oxygen. So, a common question is, if there’s no oxygen in space, why is the sun on fire?
Well, the short answer is it is not on fire the same way as your fire in your campsite. It is not burning any wood or using oxygen, but instead it is powered by a completely different process. It is a system that does not need oxygen at all. Let’s dive deeper.
Fire Needs Oxygen — But the Sun Isn’t That Kind of Fire
On our planet, fire is generated using a chemical reaction called combustion, where oxygen comes into contact with a fuel like gasoline or wood. The reaction from this process would then release light and heat, which we often see with our naked eyes as flames. But if you remove the oxygen from this process, the fire would quickly go out.
The space, however, is a different environment from Earth. Between the planets, stars, and other celestial bodies, there is no thick air that could be full of gas with oxygen. Even if there are some stray dust or atoms of specific elements, the overall amount of oxygen would still be too little for us to breathe in.
So, if the sun were just a ball of gas on chemical fire, it probably would have gone out a long time ago, but it didn’t. It was because the energy of the sun comes from inside its core. In this location, there is a different type of process that is happening than that of a combustion process that often generates fire on Earth.
Read more: Science.Nasa
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How the Sun Really Makes Light and Heat: Nuclear Fusion
Our sun is made up of mostly hydrogen gas, with some helium and a hint of other elements. Inside its core, the temperature could reach upwards of 15 million °C or 27 million °F. Not only that, but the pressure is also enormous, so much that the hydrogen atoms are squeezed together, resulting in their fusion into helium. This process is called Nuclear Fusion.
So, instead of being a combustion process where oxygen is needed, it is a nuclear reaction between the nuclei of the atoms themselves. So, when four hydrogen nuclei collide and fuse into helium, a tiny bit of mass is lost. According to Dr. Albert Einstein’s famous equation, E = mc², the mass that was lost turned into energy.
This fusion between the nuclei is what is most likely powering the sun’s heat and energy. This reaction does not need oxygen; instead, it needs a massive amount of pressure and a hot temperature for the fusion to continue happening. Because of the sun’s gravity, the gases are being crushed inward, which keeps the core hot and dense, resulting in continuous nuclear fusion.
Author's Final Thoughts
Aside from not needing oxygen, the gas that is pressurized and heated is actually in a state of matter called plasma. So, the conditions for the process for the sun being hot are completely different than those of a fire on Earth. This hot plasma is also what makes it look like it is on fire, because it glows brightly. We see that glow as sunlight on the planet. But what it actually was is a byproduct of a nuclear fusion reaction of the sun.
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