Hydrogen is the most abundant element in the universe. Out of all the matter visible in the cosmos, hydrogen comprises 73% of it. Helium comprises 25%, meaning every element other than hydrogen and helium comprises a mere 2% of the total visible matter in the universe. If hydrogen were not the most abundant element in the universe, the world we find ourselves in would look a lot different than it does.
Hydrogen is what makes the stars, and without it, no other elements would exist. This is because every other element is descended from hydrogen. Being the simplest element in the cosmos, perhaps it’s no surprise that hydrogen both came first and is so abundant. After the Big Bang some 13.8 billion years ago, energy condensed to form the first subatomic particles such as electrons and quarks. Soon after that, quarks came together in threes to form the first protons and neutrons. It was at this moment, only within the first minute of time, that hydrogen was born. Temperatures in the early universe were so high that for a very brief moment, hydrogen nuclei fused together to form small amounts of helium and lithium. However, every other element on the periodic table did not exist yet. In order for every other element to form, the stars needed to form first.
Stars come in a wide variety of sizes, colours, and masses, yet they all begin their lives in virtually the same way. A vast cloud of hydrogen gas clumps together, causing both temperatures and pressures to rise dramatically. As soon as temperature exceed ten-million degrees kelvin, hydrogen undergoes a process called nuclear fusion. Two protons may fuse together to form deuterium: a form of hydrogen composed of one proton and one neutron (upon fusing, one of the protons decays into a neutron). After the deuterium forms, it may fuse with another deuterium to form helium nuclei. This process of fusing atoms together generates a tremendous amount of energy. So long as nuclear fusion is occurring with the star’s core, it is defined as a main sequence star.
The energy generated from the core is so large that it counteracts the immense gravitational pull of the star, creating a state of equilibrium that maintains the star. So far we have only discussed how we end up with helium, yet the process of nuclear fusion doesn’t stop there. Through a series of events called the Triple Alpha Process, stars can eventually form carbon. During this process, two helium nuclei fuse together to form a beryllium nuclei. Further still, these beryllium nuclei can fuse to helium nuclei to form carbon. If it were not for the stars, carbon would not exist, and hence life itself could never hope to form. Image credit: NASA/ESA, Hubble
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