Stellar Evolution

Section 1: Stellar Birth and Formation

Stars begin as a nebula, a large cloud of gas and dust in space.
In regions of a nebula where gravitational force is strong, these gases and dust clump together to form a protostar.
As the protostar grows, its gravitational pull increases, drawing in more particles and heating up its core.
Once the core temperature hits million of degrees, nuclear fusion begins - a process where hydrogen atoms combine to form helium, emitting large amounts of energy. This marks the birth of a star.

Section 2: Main Sequence Stars

The majority of a star’s life is spent in the main sequence phase, where it burns hydrogen to form helium.
A star’s position in the main sequence depends on its mass: larger stars are hotter and shine more brightly.
During this phase, gravitational forces pulling inwards are balanced by the radiation pressure from the fusion reactions pushing outwards. This creates a state of hydrostatic equilibrium within the star.

Section 3: Red Giants and Super Giants

As stars exhaust their hydrogen fuel, the outward pressure decreases leading to an imbalance in the hydrostatic equilibrium.
This causes the star to contract under gravity, which in turn increases the core temperature and the rate of fusion.
The outer layers expand due to the increased heat and the star becomes a red giant or a red super giant, depending on its initial mass.
The star continues to burn heavier elements until it reaches iron, where no more fusion can occur.

Section 4: Final Stages of Stellar Evolution

The final stages of a star’s life vary depending on its mass.
Low and medium mass stars, like our Sun, shed their outer layers creating a planetary nebula and leaving behind a hot, dense core called a white dwarf. Over billions of years, this cools to form a black dwarf.
High mass stars end as supernovae, explosive events that blast elements into space and can result in either a neutron star or a black hole, depending on the mass of the collapsing core.

Section 5: Gravitational Attraction and Stellar Evolution

The force of gravitational attraction plays a key role in stellar evolution, from the formation of protostars to the creation of black holes.
The balance between gravitational force and other forces like radiation pressure determines the life cycle and final fate of a star.
Gravity, therefore, is the principal architect of the universe, shaping galaxies and structuring the cosmos.