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1. Star Life Cycle and
Nuclear Fusion

2. Nuclear Fusion. It is a nuclear process,
where energy is produced by smashing
together light atoms

3. Stellar Evolution: Life of the
Star
 The most massive stars have the
shortest lives. Stars that are 25 to 50
times that of the sun live for only a
few million years. Stars like our Sun
live for about 10 billion years. Stars
less massive than the Sun have even
longer life spans
 Stars are like humans they are
born, live and die

4. Stars are formed in
1. Nebulae, interstellar clouds of dust and gas
(mostly hydrogen).
These stellar nurseries are abundant in the arms
of spiral galaxies.
In these stellar nurseries, dense parts of these
clouds undergo gravitational collapse and
compress to form a rotating gas globule.
The Birth of Stars
It begins to spin as it shrinks

5. NEBULA PICTURES

6. Protostar stage: The nebula flattens and
the center condenses:
Temps start to increase due to friction
(more collision of molecules).
When temps reach 10 million K, NUCLEAR
FUSION begins
Nuclear Fusion generates the energy for a
star.
When fusion begins, it is officially
considered a STAR. (yeah!)
Fusion – combining a lightweight nuclei
into a heavier nuclei

7. Protostar
Pictures

8. Stars live out the
majority of their lives in
a phase termed as the
Main Sequence.
Longest stage of a star
The protostar is now a
stable main sequence
star which will remain
in this state for about 10
billion years. After that,
the hydrogen fuel is
depleted and the star
begins to die.
Main-Sequence Stage

9. Main Sequence Star

10. When a star has burned between 10% and 20% of its hydrogen,
its core will to run out of fuel.
At this stage, the star is entering the end of its life.
The diameter of the star can increase by a factor of 200, while its
cooling is translated into a reddening of its radiation : the star is
becoming what is called a red giant.
RED GIANT STAGE

11.  Star has run out of Hydrogen
atoms in the core to undergo
fusion.
 Our sun has used only about 5%
of its Hydrogen
 Star expands about 10x bigger
and cools.
 Its luminosity increases, temp
decreases.*****
 Helium fuses to form Carbon, and
the core shrinks.
 It begins losing outer layers

12. BETELGEUSE –RED GIANT
 Only a few million years
old, Betelgeuse is already
dying. Astronomers
predict that it's doomed to
explode as a soon, within
1,000 years or so, an event
that will be spectacular for
Earth's future inhabitants.
(Conceivably, it's already
happened as Betelgeuse is
640 light-years away!)
F.Y.I.

13. Burnout and Death
 Fate of a Star depends on
its mass
 All stars, regardless of
size, run out of fuel and
collapse due to gravity
 A star will become
either a black dwarf,
neutron star, or
black hole,
depending on how
massive it was. .

14. Death of low-mass stars
 Remain stable main-sequence stars until
hydrogen is gone
 Collapse into white dwarfs

15. **Death of medium-mass stars**
 Sun-like Stars
(Mass under 1.5 times the mass of the Sun) Red
Giant --> Planetary Nebula -->White Dwarf
--> Black Dwarf

16. **Death of massive stars**
 Huge Stars
(Mass between 1.5 to 3 times the mass of the Sun)
Red SuperGiant --> Supernova --> Neutron Star
 Giant Stars
(Mass over 3 times the mass of the Sun) Red
SuperGiant --> Supernova --> Black Hole

18. PLANETARY NEBULA
 This is left when a giant loses its outer layers
of gas.
 Leaves only the core.
 The core will become a white dwarf

19. Planetary nebula pictures

20. WHITE DWARF
Only hot, dense core is left of this star.
 It will shine for billions of years before
cooling.
 Stable star with no nuclear fuel,radiates left
over fuel for billions of years
 Could become a black dwarf, but the
universe is not old enough to form these

21. White Dwarf Pictures

22. SUPER NOVA
 Super Giant eventually
loses its outer layers in an
explosion leaving only
the core – this is the
super nova.

23. NEUTRON STAR
 After a Super Nova explosion, the core may
condense into a small core of neutrons.
 It is so dense – 1 spoonful of Earth would weigh
100 million tons.
 Rotates very rapidly.
If the star's remaining mass is between 1 1/2 to 3 times the
mass of the Sun, it will collapse into a small, dense
neutron star (about ten miles in diameter, about 1.4 times
the mass of the Sun, with an extraordinarily strong magnetic
field, and rapid spin).

24. Neutron Star Pictures

25. BLACK HOLE
 This is the 3rd predicted result to a star.
 This is the most dense core of a star that
can be left.
 Gravity is so strong, light cannot escape.
 Makes it look like a dark hole in space.
If the star's remaining mass is greater than three times
the mass of the Sun, the star contracts tremendously
and becomes a black hole

26. Black Hole Pictures
Anatomy of a black hole

27.  The density of a star is pre-determined based
on its weight (the amount of dust and gas)
it begins with.
 Smaller stars become white dwarfs.
 Very large stars become neutron stars or
black holes.
•Life Cycle of a
Star Video