SPACE — We all know that the universe contains a variety of elements, ranging from light gases such as helium, to heavy metals such as lead. But where do all those elements come from?
The journey of the elements of the universe began in the early moments of the Big Bang, when our universe was only a few seconds to minutes old. At that time, the entire cosmos was crammed into a volume millions of times smaller than today’s volume.
Due to its extremely high density, the average temperature of all matter in the universe is over one billion degrees, which is more than hot enough for nuclear reactions to occur. It is so hot that protons and neutrons cannot exist as stable entities. Instead, the universe is just a sea of fundamental particles, called quarks and gluons, churning around in a state of raw plasma.
But the universe will not last long. It expands, which means it also cools. Ultimately, quarks were able to bond to form the first protons and neutrons without being destroyed immediately. Protons are slightly lighter than neutrons, giving them an advantage in the early stages of producing these particles.
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When the universe was only a few minutes old, it was too cold to produce new protons and neutrons. So, those first few heavy particles are the only ones that will form in the universe (outside of rare high-energy interactions in the future).
By the time the heavy particles finally freeze, there are about six protons for every neutron. Neutrons themselves are unstable; they decompose with a half-life of about 880 seconds. Soon, some of the neutrons began to decay, while the rest began to bond with protons to form the first atomic nuclei.
Of all the light elements, helium-4, which consists of two protons and two neutrons, has the greatest binding energy. This means that it is the easiest to form and the most difficult to decompose. So almost all the helium at that time was used for helium-4 production.
From such calculations, cosmologists can estimate that the universe began with a mixture of about 75 percent hydrogen (which is just protons), 25 percent helium, and small amounts of lithium. They are what astronomers can observe.
The next stage in the emergence of these elements had to wait for the first generation of stars, which only began to shine hundreds of millions of years after the Big Bang. Stars generate power through nuclear fusion, converting hydrogen into helium. This process leaves little energy. But stars have so much hydrogen that they can burn for billions, or sometimes trillions of years.
Towards the end of their lives, stars like the sun turn to fused helium, turning it into carbon and oxygen before dying as planetary nebulae. That is why carbon and oxygen are so abundant in the universe.
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After hydrogen and helium, carbon and oxygen are the most commonly produced elements. Oxygen is also the most common element on Earth, although most of it binds with silicates to form the soil beneath our feet.
More massive stars, those with masses at least eight times the mass of the Sun, fuse heavier elements into their cores. Especially in their final weeks, days and even hours, the most massive stars in the universe produce nitrogen, neon, silicon, sulfur, magnesium, nickel, chromium and iron.
2023-10-23 11:20:00
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