Stellar evolution begins with nebulae, large clouds of gas and dust where stars form under the influence of gravity. As nebulae contract under their own gravity, the pressure and temperature increases, forming glowing protostars at the centers of contracting gas clumps. Once the core is dense and hot enough, nuclear fusion of hydrogen to helium begins, releasing energy and marking the birth of a star. The size of a star is determined by the balance between gravitational collapse and pressure from nuclear fusion. Over their lifetimes, stars evolve from the main sequence through red giant phases as their cores shrink and outer layers expand and cool. The final fate of a star depends on its original mass, becoming a white dwarf, neutron star, or black

1. STELLAR EVOLUTION
BY
SHANKAR

3. NEBULAE
• Stars form from nebulae which a large clouds
of gas mainly hydrogen and some dust and
heavier elements.
• These clouds are very huge.
• The only force acting on the particles of the
nebulae is gravity.

5. GRAVITY ON NEBULAE
• Gravity slowly pulls the gas.
• When this happens the nebulae contracts.
• Contraction leads to a higher pressure , thus a
higher temperature. Higher temperature
makes these clumps of dust glow.
• It contract even more , leading into an even
higher temperature. The clump makes a
spherical shape and glows even more. This is
called PROTOSTAR.

6. NUCLEAR FUSION
• Particles in the core are packed close together
and moving faster now hydrogen nuclei is
make helium nuclei.
• Nuclear fusion has begun release the huge
amount of energy.
• In this stage A STAR IS BORN.

7. SIZE OF A STAR
• The size of the star determined by very
delicate balance.
• Gravity always wants to make the star small.
Gravity wants to collapse the star.
• But the nuclear fusion produces the heat,
produces the pressure through the out side.

8. ..
• The size of the star determined by this
balance.
• If the thermonuclear fusion would increase in
strength the star becomes bigger.
• If it decrease in strength the star will shrink.

9. RED GIANT
 IN CASE OF A AVERAGE STAR LIKE OUR SUN.
 When the gravitational force are weakening ,
thermal force is slowly wining cause the star
to expand .
 As a star expand it is cooling , these larger
cooler stars are called RED GIANT.

10. ENDING STAGE
• Thermal forces are weakening , sooner the
gravity again wins.
• The core of the red giant collapses into a small
white dwarf.
• Where the star ends up at the end of its life
depends on the mass it was born with.
• When a star born with the 8 times mass of our
sun it will become a white dwarf.

11. Chandrasekhar limit
• Chandrasekhar calculated the maximum mass
of a white dwarf,
• It can only be 1.4 times mass of our sun.
• If the mass become longer the white dwarfs
become unstable and collapse.

12. Ending of massive stars
• When a star born with 8 to 25 solar mass it
will become a NEUTRON STAR.
• Neutron stars are purely made up of neutrons,
the neutron stars would be formed in
supernova explosion.
• When a star born with more than 25 solar
mass it will become a BLACKHOLE.

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