Approximately 73% of the accumulation of the arresting cosmos is in the anatomy of hydrogen. Helium makes up about 25% of the mass, and aggregate abroad represents alone 2%. While the affluence of these added massive ("heavy", A > 4) elements seems absolutely low, it is important to bethink that a lot of of the atoms in our bodies and Earth are a allotment of this baby allocation of the amount of the universe. The low-mass elements, hydrogen and helium, were produced in the hot, close altitude of the bearing of the cosmos itself. The birth, life, and afterlife of a brilliant is declared in agreement of nuclear reactions. The actinic elements that accomplish up the amount we beam throughout the cosmos were created in these reactions.
Approximately 15 billion years ago the cosmos began as an acutely hot and close arena of beaming energy, the Big Bang. Immediately afterwards its formation, it began to aggrandize and cool. The beaming activity produced quark-antiquarks and electron-positrons, and added particle-antiparticle pairs. However, as the particles and antiparticles collided in the top activity gas, they would abate aback into electromagnetic energy. As the cosmos broadcast the boilerplate activity of the radiation became smaller. Atom conception and abolishment connected until the temperature cooled abundant that brace conception became no best agilely possible.
One of the signatures of the Big Bang that persists today is the long-wavelength radiation that fills the universe. This is radiation larboard over from the aboriginal explosion. The present temperature of this "background" radiation is 2.7 K. (The temperature, T, of a gas or claret and boilerplate atom active energy, E, are accompanying by the Boltzmann constant, k = 1.38 x 10-23 J/K, in the blueprint E = kT.) The temperature at assorted stages in the time change of the cosmos from the quark-gluon claret to the present time.
n + p Æ d + g. d + n Æ 3H + g and d + p Æ 3He + g. d+ d Æ 4He + g, 3He + n Æ 4He + g and 3H + p Æ 4He + g.
Approximately 15 billion years ago the cosmos began as an acutely hot and close arena of beaming energy, the Big Bang. Immediately afterwards its formation, it began to aggrandize and cool. The beaming activity produced quark-antiquarks and electron-positrons, and added particle-antiparticle pairs. However, as the particles and antiparticles collided in the top activity gas, they would abate aback into electromagnetic energy. As the cosmos broadcast the boilerplate activity of the radiation became smaller. Atom conception and abolishment connected until the temperature cooled abundant that brace conception became no best agilely possible.
One of the signatures of the Big Bang that persists today is the long-wavelength radiation that fills the universe. This is radiation larboard over from the aboriginal explosion. The present temperature of this "background" radiation is 2.7 K. (The temperature, T, of a gas or claret and boilerplate atom active energy, E, are accompanying by the Boltzmann constant, k = 1.38 x 10-23 J/K, in the blueprint E = kT.) The temperature at assorted stages in the time change of the cosmos from the quark-gluon claret to the present time.
At first quarks and electrons had only a fleeting existence as a plasma because the annihilation removed them as fast as they were created. As the universe cooled, the quarks condensed into nucleons. This process was similar to the way steam condenses to liquid droplets as water vapor cools. Further expansion and cooling allowed the neutrons and some of the protons to fuse to helium nuclei. The 73% hydrogen and 25% helium abundances that exists throughout the universe today comes from that condensation period during the first three minutes. The 2% of nuclei more massive than helium present in the universe today were created later in stars.
The nuclear reactions that formed 4He from neutrons and protons were radiative capture reactions. Free neutrons and protons fused to deuterium (d or 2H) with the excess energy emitted as a 2.2 MeV gamma ray,
These deuterons could then capture another neutron or free proton to form tritium (3H) or 3He,
Finally, 4He was produced by the reactions:
Substantial quantities of nuclei more massive than 4He were not made in the Big Bang because the densities and energies of the particles were not great enough to initiate further nuclear reactions.
It took hundreds of thousands of years of further cooling until the average energies of nuclei and electrons were low enough to form stable hydrogen and helium atoms. After about a billion years, clouds of cold atomic hydrogen and helium gas began to be drawn together under the influence of their mutual gravitational forces. The clouds warmed as they contracted to higher densities. When the temperature of the hydrogen gas reached a few million 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.
It took hundreds of thousands of years of further cooling until the average energies of nuclei and electrons were low enough to form stable hydrogen and helium atoms. After about a billion years, clouds of cold atomic hydrogen and helium gas began to be drawn together under the influence of their mutual gravitational forces. The clouds warmed as they contracted to higher densities. When the temperature of the hydrogen gas reached a few million 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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