There's no atmosphere in space... so how does a big hydrogen ball keep burning?
Of course, if we insist, most of us would explain that the Sun is not actually in the sky. No bird will accidentally fly in and become a crispy chicken sandwich. Instead, it is in space, approximately 91 million kilometers from us. The Earth is orbiting the Sun, and so are the other planets in our solar system.
But there's a riddle here. When most of us learn about fire, we are taught to need three components: heat, a fuel source, and oxygen. Remove these three factors, and the fire dies out. (That's why you can smother a fire—you take the oxygen out of it.
However, the air is not present in space. Once you leave the Earth's atmosphere, you don't have any oxygen, unless you take it with you.
How is the sun on fire? If it's a large ball of hydrogen, where's the oxygen to keep it on fire?
As a matter of fact, the sun doesn't burn like our campfires. Here's the way this works.
Combustion, Fission, or Fusion?
When we're talking about something that burns, we're usually talking about something called combustion.
Combustion is a chemical reaction in which a fuel interacts with an oxidant, forming new bonds and giving off energy.
Once you add enough heat in a circumstance with a fuel and oxidant present. weak bonds of the oxidant are broken and stronger bonds are formed with the fuel, leading to energy release.
This reaction can become self-sustaining, in other words, fire can develop as long as all the ingredients are present. But get one of the three feet off the stool, and it collapses. Run out of oxidant, fuel, or heat? Fire is going off.
But there are other kinds of reactions that unleash energy.
The next reaction is called fission, which happens when a big atom separates. The most famous example is the fission of uranium atoms in early nuclear bombs.
Large atoms, like uranium or plutonium, are unstable. When they are hit by a little particle, like a piece of the atom, they break. This small mini-blast gives off energy but also sends out more fragments. These fragments can strike other uranium atoms, breaking them down into more pieces, in turn, causing an energy-releasing chain reaction.
Finally, we have fusion. Fusion is the opposite of fission; it's the process of mixing smaller atoms to create a bigger atom. This also leads to a release of energy - and also to the creation of a heavier element!
You can smash two hydrogen atoms, for example, and form a helium atom. Smashing helium atoms together, and at the same time, we have heavier elements. This process continues, though as each atom grows, it becomes more difficult to force it to continue the fusion reaction.
So, our three different methods of fire:
- Combustion releases energy when atoms are broken up.
- Fission liberates energy when you separate a large atom into pieces.
- Fusion releases energy when we combine small atoms into one bigger and heavier atom.
The Sun is a fusion bomb that has been flaring up for more than 9 billion years.
Of these three forms of energy production, what fire explains the Sun?
The answer is fusion! Our Sun started as a giant ball of hydrogen, created when the universe was younger. As this massive ball of hydrogen gathered, gravity pulled the atoms closer and closer until they began to fuse. which unleashed energy in space around the forming star.
Remember that fusion requires no oxygen to trigger the reaction. It just needs enough power to force individual atoms to fuse.
The immense heat and pressure in the heart of the Sun act as the forge which fuels the current reaction.
But while our Sun needs no oxygen, this response still needs fuel.
This is where the enormous hydrogen cloud kicks in. the Sun is literally made of the fuel it burns, in a huge and continuous fusion reaction, to pump the incredible levels of energy. that warm up all the planets and make life possible on Earth.
But what happens when the Sun doesn't have enough hydrogen?
Alternative Fuels, Solar Edition
Fortunately for us, a fusion response does not only work with hydrogen. Other components may also be used as fuel, assuming good conditions.
Right now our Sun is burning hydrogen—an enormous amount, about 600 million tonnes of hydrogen per second. This hydrogen becomes helium.
As the hydrogen supply declines, the Sun will begin to use helium in its fusion response. This will slightly shrink the Sun, but will get hotter - and as more energy is produced by the fusion of helium than hydrogen, it will produce more energy.
(These are likely to kill our planet. Over the next four and eight billion years. the increasing intensity of the energy produced by the sun will cook the Earth. boiling our oceans and burning only bare, carbonized rocks.)
As more and more hydrogen is converted into helium, the denser helium accumulates at the core of the Sun, pumping more and more energy as it compresses.
Eventually, this will fuse with even heavier elements, like carbon, while the sun's outer layers. always made of remaining hydrogen, is going to extend to swallow Mercury and approach Venus.
Eventually, this outer layer will fly off as it consumes itself, spreading through the entire solar system as it escapes. An incredibly dense core will be left behind, barely more than half the original mass of the Sun, amidst the burnt remnants of our solar system.
This fusion reaction will ultimately destroy our Sun and the whole solar system. but that won't happen for billions of years, so we don't need to worry too much!
When we talk about Sun Burn (if we are not talking about radiation-induced skin injuries), we are talking about a reaction that releases energy. But unlike earthly reactions to ignite something, the Sun does not need oxygen or another oxidant to burn.
Instead, while our fires on Earth have just released energy in the bonds between atoms, the fire of the Sun releases energy from the atoms themselves. It's a gigantic fusion reactor that fuses hydrogen into helium to create energy.
We still use combustion on Earth because it is difficult to generate conditions similar to those found in the Sun to conduct our own fusion reactions. However, perhaps one day soon we may have our own tiny Sun-like fusion reactions that will produce power for us.
In the meantime, we can fuel the giant fusion reactor in our skies—through solar panels.
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