“Every star will someday run out of fuel in its core, bringing an end to its run as natural source of nuclear fusion in the Universe. While stars like our Sun will fuse hydrogen into helium and then – swelling into a red giant – helium into carbon, there are other, more massive stars which can achieve hot enough temperatures to further fuse carbon into even heavier elements. Under those intense conditions, the star will swell into a red supergiant, destined for an eventual supernova after around 100,000 years or so. And the brightest red supergiant in our entire night sky? That’s Betelgeuse, which could go supernova at any time.”
One of the most sobering cosmic truths is that every star in the Universe will someday run out of fuel and die. Once its core fuel is exhausted, all it can do is contract under its own gravitational pull, fusing heavier and heavier elements until it can go no further. Only the most massive stars, capable of continuing to fuse carbon (and even heavier elements) will ever create the Universe’s ultimate cataclysmic event: a Type II, or core collapse, supernova. Stars that are fusing carbon (and up) appear to us today as red supergiants, and the brightest red supergiant as seen from Earth is Betelgeuse. Sometime in the next 100,000 years or so, Betelgeuse will go supernova. When it does, it will emit incredible amounts of radiation, become intrinsically brighter than a billion suns and and be easily visible from Earth during the day. But that’s not all.
This process uses the helium in a star’s core. For a refresher on how helium is made, click HERE for a detailed explanation and HERE for a simpler version.
As stars fuse hydrogen into helium, they eventually run out of hydrogen in their core to fuse. When the core is 100% helium, the star begins to collapse, since the outward push from fusion (which balances the inward pull of gravity) is no longer active. The star’s collapse heats up the core until the helium begins to fuse. The helium begins fusing very rapidly, and we call this the helium flash. It’s quite literally a flash too - the star’s brightness rapidly increases. The heat from this reaction heats up the outer layers of the star, which are made of hydrogen, which then begin to undergo proton-proton fusion to create helium.
Below is the reaction that occurs, turning helium into carbon:
This is how Carbon is formed - two helium nuclei combine to form Beryllium, followed by a third Helium fusing with the Beryllium to create Carbon. It’s called the triple-alpha process because this process uses three Helium nuclei, which are also called alpha particles. This process also releases energy, since Carbon nuclei are more stable than Helium nuclei. Since energy is released, the inward pull of gravity is then counteracted by the outward push from fusion, so the star is stable again.
The moment you’ve all been waiting for!! So basically, stars create energy by fusing elements together in the very hot and very dense core - elements are literally smashed together to make new elements. The energy given off by fusion creates an outward force that counteracts the collapsing force of gravity, which allows stars to be (relatively) stable and stay round without collapsing or exploding. Stars start out fusing Hydrogen into Helium, and then move on to fuse heavier elements together when it runs out of Hydrogen. In order for fusion to take place, it must be very hot and very dense, which is why it mainly happens in stars.
As fusion occurs, a small part of the mass contained inside the fusing elements is turned into energy. Using the famous equation E=mc2, you can calculate how much energy is released during each reaction. However, I will not be calculating that for you guys (at least for now), and instead I’ll just stick to the basic reaction converting hydrogen into helium. There are three different proton-proton chains, and I will be including each one.
Notation review and conservation laws link (not up yet bc this isn’t published)
The foundation of the nuclear power that provides us with so much electricity is harnessing the energy that’s contained within atoms. In layman’s terms fission is the division of an atom into two and fusion is combining two into one.
Nuclear fission occurs when a large, unstable isotope is bombarded by a high speed neutron (it can be other high speed particles but normally it’s a neutron). The neutron collides with the target nucleus and splits it into two smaller isotopes releasing a lot of energy in the form of heat. 3 high speed neutrons are also produced that go on to collide with the nuclei of other isotopes thus continuing the reaction. The high speed electrons that are ejected by this process also initiate fission reactions. In most nuclear reactors Uranium-235 is the isotope they use, the energy resulting from fission is used to heat water which turns a turbine and that’s essentially how nuclear reactors produce electricity.
Fusion is what powers the sun and is unlikely to ever occur on earth because we have yet to find a way to contain such a massive amount of energy. The fusion between two nuclei with lower masses than Iron-56 generally releases energy while the fusion of nuclei heavier than iron requires energy. Our sun is currently fusing the nuclei of Deuterium and Tritium (Hydrogen-2 and Hydrogen-3) to form Helium isotopes which releases several times the amount of energy produced by fission. When all the Hydrogen isotopes are used up, the sun will start to fuse the nuclei of the Helium that’s there. Some stars (not our sun because it’s too small) will keep fusing nuclei together until eventually the core is made of solid iron at which point it will die, fire the matter it has spent it’s life creating across the galaxy and then what’s left over would be a neutron star. Larger stars have the energy to make isotopes heavier than iron and what’s left behind when these die is a black hole. So the carbon that makes up life as we know it first came into existence at the heart of a star like that. So for us to live, it meant a star had to die.
Moussa (1917-1952) was an accomplished Egyptian nuclear physicist. After
completing her studies at Cairo University, she became the first woman to hold
a PhD in atomic radiation, as well as the first woman to hold a university post
when she became an assistant professor there.
She worked hard to make nuclear technology available widely for its uses
in medicine, and her research led to the discovery of a way to break the atoms
of certain metals such as copper. She organized the Atomic Energy for Peace
Conference, which brought together scientists from all over the world.
Trinitite: this piece of green glass was produced by the heat of the very first atomic explosion. Trinitite is the name given to the fused sand from the Alamagordo NM fission bomb test on July 16, 1945- code named Trinity. The 20 kiloton explosion melted the top few centimeter think layer of the desert sand out to a radius of a kilometer. Still mildly radioactive (as seen with this vintage Civil Defense Geiger Counter) but safe to handle. A piece of physics history! ➡️ Follow the link in my profile for info and on where to get this and many more of the amazing items featured here on @physicsfun
Cherenkov radiation - faster than light in a meduim.
Vavilov-Cherenkov radiation is electromagnetic radiation emitted when a charged particle (in this case the electron) passes through an electrically polarizable medium at a speed greater than the phase velocity of light in that medium - in cherenkov radiation, electrons are emitted faster than than the speed light travels in water.
light travels through water at 0.75c (thats 75% the speed of light in a vacuum). Matter can be accelerated beyond this speed during nuclear reactions and in particle accelerators.
Cherenkov radiation is used in particle physics to identify types of particles. One could measure the velocity of an electrically charged elementary particle by the properties of the Cherenkov light it emits in a certain medium. If the momentum of the particle is measured independently, the mass of the particle can be computed by its momentum and velocity, and with this identify the particle.
The radiant blue glow of an underwater nuclear reactor is due to Cherenkov radiation. It is named after the Soviet scientist and Nobel Prize winner Pavel Alekseyevich Cherenkov, who discovered it in 1958 through experiment.
50 ktons of water, 3000 feet underground, almost 40m by 40m in size, build by thousands of 10 humans to detect almost massless particles (neutrinos). change type from one to another as they pass through earth to the other side of the planet. The universe does pretty interesting things!