Part of what makes fusion such a promising source of energy is the fact that deuterium is easily extracted from ordinary seawater. Tokamaks are often also called 'artificial suns' due to the fact these doughnut-shaped machines replicate processes that occur in the sun. ![]() The devices designated with the task of doing this here on Earth - nuclear fusion reactors - are called tokamaks. ![]() Humanity can't bring the cores of stars down to Earth, so the next best thing is replicating the dense gas of plasma found at the heart of the sun. Bringing nuclear fusion power down to Earth This material from these dead stars becomes the building blocks of the next generation of stars, the planets, and everything around us, including our own human bodies.Īdditionally, shockwaves from the compressing iron core - which will eventually birth a neutron star or even a black hole - hit gas shed by the supernova triggering further nuclear fusion creating elements heavier than iron and radioactive materials as well as blasting out x-rays and gamma-rays. This triggers a supernova that flings the elements the star has forged during its lifetime out into the universe. When all nuclear fusion ceases, the star undergoes a final and catastrophic gravitational collapse. This is because iron is an extremely stable element and stars aren't massive enough to trigger its fusion. This progression of nuclear fusions ends even for the most massive stars when iron dominates the stellar core. As this continues, the star develops an onion-like structure with lighter elements fusing in its outer layers and subsequently heavier elements being created towards the core.Ī close-up of the sun depicting solar surface activity and the corona. When helium is exhausted, collapse occurs again triggering the fusion of even heavier elements. That means that when fusion ceases, so goes the outward pressure this results in the collapse of the star and the swelling and loss of its outer layers.įor stars more massive than the sun - which will end its life as a smoldering white dwarf - this gravitational collapse creates enough pressure to trigger the nuclear fusion of helium created by the main sequence lifetime in its core, fusing it to create carbon, neon and oxygen. The energy generated by fusion serves a vital purpose within stars, providing the outward pressure that balances the ball of plasma against the inward force of gravity. The NO cycle is similar but uses nitrogen-14 as a catalyst. Carbon-12 through proton capture goes through various stages until a helium atom is emitted and carbon-12 is recovered. The CN cycle begins with the nucleus of a carbon-12 atom using it as a catalyst - an element that speeds up a reaction but is unchanged at the end of it - for fusion. Instead, most of these stars' energy comes from the carbon-nitrogen-oxygen (CNO) cycle which requires the higher temperatures of more massive stars to get started. The PPI isn't the main fusion reaction in more massive stars than the sun, however. When and where do stars forge heavier elements? How does nuclear fusion forge the chemical elements?Īstronomers describe stars as containing hydrogen, helium and everything else (with elements heavier than helium described as 'metals' by astronomers) and these other elements also play a role in fusion. But, helium isn't the only chemical element being forged in the sun. This hydrogen-burning helium forging phase is what astrophysicists call the main sequence lifetime of a star. That equates to about 260 billion Joules, enough energy to power a 60-watt light bulb for about 100 years.īecause of its tremendous hydrogen content, the sun has maintained this fusion rate for around four and a half billion years and will continue to do so for a further four and a half billion years until the hydrogen in its center is exhausted. If four grams of hydrogen were converted to helium through this process, only 0.0028 grams would escape as energy. During this time the photons are undergoing a series of collisions, absorptions, and re-emissions, which 'downgrade' their energy to photons of visible light eventually radiated out by the photosphere.Įach occurrence of the PPI radiates about 0.0000000000044 Joules, which means - ignoring the other fusion process going on in the sun - our star has to complete this process about 9x10³⁷ (9 followed by 37 zeroes) times every second to maintain its luminosity! These photons will struggle to escape the star's dense interior, however - taking over 30,000 years to move from the core to the surface. While some of the energy is carried away as the kinetic energy of the daughter particle, the majority is carried by the two gamma-ray photons. ![]() (Image credit: Mark Garlick/Getty Images) Four protons (hydrogen nuclei) are combining on the left, releasing in the process two protons and two neutrons (a helium nucleus). An illustration of the process of nuclear fusion, specifically the creation of helium from hydrogen.
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