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In: Planetary Science
The sun is a huge ball of mostly-hydrogen. If you’re in the middle of it you’re under incredible pressure, because there’s thousands of kilometers of hydrogen sitting on top of you. That pressure is so intense it can crush atoms together. Generally two atoms of hydrogen get mashed into each other and that produces a helium atom, and a massive amount of heat.
The sun is blazing hot because of the fusion heat being produced at its core. That heat works its way up out of the core toward the surface, and the glowing-hot surface radiates heat, light, ultraviolet, X-rays and gamma rays out into space. That radiation gets to Earth, fortunately our atmosphere soaks up most of the really deadly stuff, and what we get is mostly heat, visible light and a touch of UV.
The Sun is roughly 5 billion years old, and we think it has about 5 billion years left in it. Eventually it won’t have any more hydrogen in the high-pressure region, the fusion will stop and it’ll end up as a burnt-out remnant called a white dwarf.
At the most basic level, it’s a huge ball of hydrogen. It’s so massive that the gravity it creates is strong enough that the hydrogen nearer the middle is under such pressure that nuclear fusion occurs, and the hydrogen is fused into heavier elements. This releases huge amounts of radiation, including the heat we feel and the light we see.
the sun is mostly hydrogen, very very hot and extremely dense hydrogen, so hot in fact it’s not even a gas anymore it’s a plasma, just one big soup of electrons and protons
now plasma exists on earth too, lightning is a great example, but remember the sun’s temperature in the core is unimaginably hot, so this means that basically the hydrogen atoms are flying around so fast they can sometimes smash into each other so hard that despite protons being naturally repelled they can combine together and with a couple of electrons too to form helium
now you might reasonably expect that atoms smashing together takes a lot of energy, and it does, but once it happens it gives a lot more energy put than you initially put in, because of all kinds of weird reasons I don’t fully understand helium is lighter than 4 hydrogen atoms, and the difference in weight (technically mass) is converted to energy, a lot of energy
The sun started out as a large cloud of gas. Over time, gravity pulled that gas into a dense ball. As it did so, it began to heat up. Eventually the heat and pressure was so much that it started forcing hydrogen to fuse together into helium. This releases a lot of energy which counteracts the pull of gravity, so the sun settled into a stable size and shape, with its immense gravity balanced out by the constant release of energy from fusion.
A byproduct of this is all of the light the sun releases that eventually reaches earth.
Eventually, all of the hydrogen in the sun’s core will be converted into helium and the fusion process will stop. When this happens, there will be nothing counteracting gravity and the core will shrink. The hydrogen in a layer around the core will begin fusion causing the sun to expand into a red giant, possibly consuming the Earth in the process. This is estimated to happen in about 5 billion years.
After another billion years, this second layer of hydrogen will have been converted into helium, and this helium core will have built up enough heat and pressure to begin fusing into carbon. And basically a pattern emerges, with the core fusing into a heavier element until all of it is exhausted, then an outer layer around the core doing the same. Each time some of the suns outermost layers will shed, until it has expelled enough gas to create a planetary nebula, leaving a small core known as a white dwarf that will eventually fade until a black dwarf when it loses all of its energy.
I actually explained this to my twins when they were 5 and they got it!
The sun is made of hydrogen. Gravity squeezes it together. In the center it is so hot, and it is squeezed so hard, that 2 hydrogens are squeezed together and become a helium.
If you were to weigh the two hydrogens and the helium you get from them, you will find that the helium weighs a little bit less than the hydrogen you started with. Where did the extra weight go? Did the mass disappear? No! the missing mass is converted to energy. The heat and light that we see and feel is the energy.
There is a simple equation to tell you how much energy you get from squeezing 2 hydrogens into one helium, but that will have to wait until you learn multiplication.
The nucleus of an atom is governed by two forces: electromagnetism, which makes the positively charged protons want to fly away from each other; and, the strong nuclear force, which wants to hold protons and neutrons together. The strong force is…strong…but has a very short range, while the electromagnetic force does not have a limit to its range (although its strength drops off quickly with the square of the distance).
To create nuclei, then, you have to apply enough force to overcome the electromagnetic repulsion between protons to get them close enough for the strong force to grab them and bring them together. If you do that, energy is released (as long as the atom you make is lighter than iron – you *lose* energy this way if the atom is heavier than iron and gain energy if the atom splits instead). Forcing protons together this way takes a *lot* of force. In stars, this force comes from the gravity of all of its mass crushing inwards.
The mechanism for fusion is a little more complicated, involving quantum mechanics. Even the strong force isn’t strong enough to stick two protons together – neutrons are needed, since they have no electric charge and don’t repel the protons. Protons and electrons can sort of fuse into neutrons, and then neutrons can get stuck to protons, and *then* those heavier hydrogen nuclei made of a proton and one or two neutrons all together will fuse into helium. Buuuut that’s the more complicated version that isn’t super important right now. The important thing to know is that there’s a lot of stuff going on inside the Sun due to its gravity crushing all the particles together.
Energy is released as hydrogen (one proton and maybe a couple neutrons) fuses into helium (two protons and at least one, but probably at least two neutrons). That energy comes out as heat and photons. This energy pushes the atoms apart, holding them up against the crush of gravity. As fusion increases, more energy is created, which forces the atoms apart. That slows fusion down. When fusion slows down, there’s less energy and less pressure holding the atoms apart, so gravity crushes back inward. This cycle holds the Sun in equilibrium – gravity is balanced against the energy created by fusion. Stars *do* go through periods of increased or decreased activity, but overall it’s balanced.
The Sun actually puts out very little energy *per mass*. *You* create more energy per mass than the Sun. But, of course, the Sun has a *lot* of mass – 99.9% of the mass of the solar system is just in the Sun. Even a little bit of energy per mass is a *lot* of energy.
Despite being *really big*, the Sun has a finite amount of hydrogen to fuse into helium. Helium is heavier and more dense than hydrogen, so it sinks into the core and the Sun shrinks. This occurs over *billions* of years. Eventually, there won’t be enough hydrogen in the core for the Sun to fuse anymore. When this happens, there will still be enough energy and gravity to fuse hydrogen in huge, circulating currents of hydrogen and helium. With so much mass in the core, the energy from this fusion will cause the Sun to swell into a gas giant, much bigger than the Sun currently is. Eventually, the Sun will run out of hydrogen to fuse in these circulating currents, too, and fusion will stop. The Sun will contract into a white dwarf, which is only stays hot because of the heat left over from its lifetime. When *that* runs out, the Sun will become a black dwarf – a cold lump of mostly helium.
Stars with more mass have enough gravity to crush helium and cause it to fuse into heavier elements. Stars that are very massive will continue fusing heavier and heavier elements until they start fusing iron. As stated, fusing iron *takes* energy, rather than producing energy. This will cause the star to rapidly collapse, in a matter of minutes and with the outer layers of the star reaching relativistic speeds before impacting against the core. This sudden, massive impact creates a *nova*, and fuses the iron core into even more massive elements, which explode out into a nebula, which will eventually collapse from gravity into new stars and planets. The core remains as a neutron star. Even *more* massive stars don’t stop at neutron stars, collapsing into black holes.
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