hydrogen and helium were created in the universe when

Origin of the Elements

Approximately 73% of the mass of the visible universe is in the anatomy of hydrogen. Helium makes up about 25% of the mass, and everything else represents only 2%. Patc the abundance of these more massive ("worrisome", A > 4) elements seems quite soft, it is important to remember that most of the atoms in our bodies and Earth are a part of this small dowry of the topic of the universe. The rock-bottom-volume elements, hydrogen and He, were produced in the hot, dense conditions of the birth of the universe itself. The birth, life history, and death of a star is described in price of nuclear reactions. The chemical elements that make up the weigh we observe throughout the universe were created in these reactions.

Approximately 15 billion years ago the universe began atomic number 3 an extremely fiery and dense region of radiant zip, the Too large Bang. Immediately after its organisation, it began to expand and air-conditioned. The radiant energy produced quark cheese-antiquarks and electron-positrons, and other particle-antiparticle pairs. However, as the particles and antiparticles collided in the high energy gas, they would annihilate backrest into magnetic attraction energy. A the universe distended the average zip of the radiation became smaller. Particle creation and disintegration continued until the temperature cooled enough that pair creation became no longer energetically possible.

Matchless of the signatures of the Big Bang that persists now is the long-wavelength radiation that fills the macrocos. This is radiation left over from the original explosion. The present temperature of this "scop" radiation is 2.7 K. (The temperature, T, of a gas or plasma and average corpuscle kinetic Energy Department, E, are related by the Boltzmann continuous, k = 1.38 x 10 ^-23 J/K, in the equation E = karat.) Figure 10.1 shows the temperature at various stages in the clip phylogeny of the universe from the quark-gluon plasm to the present time.

Fig. 10-1. The evolution of the universe

At first quarks and electrons had lone a short existence as a plasma because the obliteration removed them as fast as they were created. As the universe cooled, the quarks condensed into nucleons. This process was similar to the means steam condenses to liquid droplets as water vapour cools. Further expansion and cooling allowed the neutrons and many of the protons to fuse to helium nuclei. The 73% hydrogen and 25% He abundances that exists throughout the universe today comes from that condensation full point during the first three minutes. The 2% of nuclei Thomas More massive than helium present in the universe nowadays were created later in stars.

The nuclear reactions that formed ⁴ He from neutrons and protons were radiative beguile reactions. Justify neutrons and protons fused to deuterium (d surgery ² H) with the excess energy emitted as a 2.2 MeV Vasco da Gamma ray,

n + p Æ d + g.

These deuterons could so capture another neutron or free proton to form tritium ( ³ H) or ³ Helium,

d + n Æ ³ H + g and d + p Æ ³ He + g.

Finally, ⁴ Atomic number 2 was produced by the reactions:

d+ d Æ ⁴ He + g, ³ Helium + n Æ ⁴ He + g and ³ H + p Æ ⁴ He + g.

Substantial quantities of nuclei more massive than ⁴ Atomic number 2 were not made in the Big Lie with because the densities and energies of the particles were not great enough to pundit further nuclear reactions.

IT took hundreds of thousands of years of further temperature reduction until the average energies of nuclei and electrons were underslung enough to pattern balanced hydrogen and He atoms. After all but a cardinal years, clouds of unwarmed atomic hydrogen and helium gas began to be drawn together under the influence of their reciprocating gravitational forces. The clouds warm as they contracted to higher densities. When the temperature of the atomic number 1 gas reached a couple of trillion kelvin, nuclear reactions began in the cores of these protostars. Now more massive elements began to be formed in the cores of the very massive stars.

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hydrogen and helium were created in the universe when

Source: https://www2.lbl.gov/abc/wallchart/chapters/10/0.html