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| Heavier Elements form inside the core of star through nuclear reactions ( source: NASA) |
The planet Earth contains various types of
elements which form soil, rocks, air, vegetation, species etc. There are nearly
118 elements in the nature. Every element has its specific properties. You will
be surprised to know that these elements were not formed at the time of Big Bang Explosion. After the Big Bang
only lighter elements like Hydrogen and Helium were formed. Then how the rest
of the element originated? How did the materials for formation of planets and
asteroids get formed?
The conditions after the Big Bang were
favourable only for the lighter elements and heavier elements were formed much
later inside the stars. This process of formation of element is called Nucleosynthesis.
Do you find the process of origin of elements in the universe complex
and mysterious? Let us discuss this process in detail.
Formation of elementary particle after Big Bang Explosion
The universe was started with the
unimaginably tremendous explosion called Big Bang. The universe was started
from very small point which had very high density of energy. After the Big Bang Explosion, the universe
started expanding. The universe was just a soup of matter and energy till the
first few fractions of second.
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| Big Bang Explosion ( Source: NASA) |
As the universe got cooled by expansion,
the formation of quarks took place. The particles and antiparticles were being
created form the energy and they were also being combined together to annihilate
and release energy. Till the one second after the Big Bang, the quarks were
having very high energy which was not allowing them to combine for the
formation of neutrons and protons.
After the one second of age, the universe
expanded and cooled down to temperature of about 100 billion kelvin (1011
K). At this temperature the electrons, protons, and neutrons had formed. But
they were moving with very high energy, so the formation of atom was not
possible. The neutrons were being created and destroyed by the reaction between
protons and electrons. The protons and electrons were being combined to form
neutrons and neutrons were decaying into protons and electrons.
With the expansion of universe, the
temperature decreased more, so the protons and electrons did not have enough
energy to collide and form neutrons. So the number of proton and neutron got stabilized
with the ratio of 7:1 respectively.
Formation of lighter elements in the universe
At
the 100 second after the Big Bang, the universe expanded to reach the temperature
of one billion Kelvin (109 K). At this temperature, neutrons and
protons collisions were resulting in the formation of nuclei. The proton was
itself the nucleus of the lightest atom Hydrogen. The neutron and the proton
combined to form nucleus of deuterium atom which is hydrogen with one extra
neutron. These deuterium nuclei collided to form nuclei of Helium. On rare
occasions, the collisions of deuterium were also resulting in the Lithium.
Birth of Stars
The universe continued to expand and cool,
the atoms of gases collected to form clouds of hydrogen gas. There were no
stars and planets present at that time. Only clouds of hydrogen gas were spread
across the distance of light years. This era is also called Dark Ages.
Once the temperature reached the 15 million
Kelvin, the hydrogen nuclei had enough energy to collide and fuse to form
Helium nuclei. This reaction resulted in the release of tremendous amount of
energy. The energy came out of core and counteracted the gravity. This resulted
in the equilibrium situation, where the inward pull of gravity was balanced by
the outward pressure of fusion energy. When this energy reached the surface, it
was radiated to the space and the star started shining.
Formation of heavier elements in the universe
The star continued to shine till the
exhaustion of hydrogen gas. When the hydrogen gas got consumed completely, the
helium was left as the product of reaction. Since the nuclear reactions had
stopped, the gravity started dominating the outward energy pressure and the star
started collapsing which increased pressure and temperature. With the rise in
the temperature, the helium started participating in nuclear reactions to form
carbon. When Helium got finished, the carbon started fusion reaction to form heavier
elements like oxygen and silicon. These chain reactions continued till the
formation of iron. The iron is most stable element. After the iron no further
nuclear reaction took place in the star and after this, the star stopped
shining.
During the end stages of life, the star
with massive size usually exploded in the form of supernova which resulted in
the nebula. The nebula had debris of star which contained these heavier
elements like carbon, oxygen and silicon etc.
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| Crab nebula contains metal rich gas ( Source: NASA) |
This debris acted as raw material for the
formation of new stars and planets. The planets formed form these materials were
rich in these heavier elements. That’s why we see abundance of silicon, carbon,
oxygen on the Earth.
The elements heavier than iron require much
larger energy. Such a large amount of energy is provided by the supernova
explosions. So elements heavier than iron are synthesised in the supernova.
Conclusion
Now we can say that all the materials that
we can see around us are produced form the Big Bang Explosion and
evolved from the hydrogen. The compounds required for supporting life are also
result of this evolution of elements in the universe.
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