Looking at the Life Cycle of Stars including protostars, nebula, red giant, super red giants, white dwarfs and black hole.

1. Warm Up 4/27
• When two Hydrogen atoms crash together,
what does it create?
• Helium
• When two Helium atoms crash together,
what does it create?
• Carbon
• When two Carbon atoms crash together,
what does it create?
• Iron

2. The Life Cycle
of a Star
Notes 7.4

3. I. What is a Star?
• A star is a ball of
plasma undergoing
nuclear fusion
• Stars give off large
amounts of energy
in the form of
electromagnetic
radiation

4. II. A Star is Born….
• Stars are formed in
a nebula
• A Nebula is a very
large cloud of gas
and dust in space

5. III. Protostars
• Dense areas of gas in
the nebula become
more dense due to
gravity
• Soon the dense areas of
gas take on a definite
shape and are called
protostars.
• Jupiter is a protostar

6. Protostars continued
• As more gas is added to a protostar,
the pressure in its core increases
• The increased pressure causes the gas
molecules to move faster, increasing
friction
• As friction increases, heat is generated
and the temperature of the protostars
core increases.

7. IV. A New Star!!!
• Once the core of
a protostar
reaches
27,000,000°F,
nuclear fusion of
Hydrogen begins
and the protostar
ignites.
• The protostar now
becomes a star. The bright spot is a new star igniting

8. Nuclear Fusion
• Nuclear fusion is the
process by which
two nuclei combine
to form a heavier
element.
• New stars initially will
fuse hydrogen
nuclei together to
form helium

9. V. Main Sequence Stars
• Once the star has ignited, it becomes a main
sequence star.
• Main sequence stars fuse hydrogen to form helium,
releasing enormous amounts of energy
• It takes about 10 billion years to consume all thy
hydrogen in a Main Sequence star.

10. Balancing Act
• Fusion pushing outwards
• Gravity pulling inwards

11. Unbalanced Forces
• Stars run out of
Hydrogen
• Hydrogen fusion stops
• Forces become
unbalanced
• Mass and gravity cause
the remaining gas to
collapse on the core

12. VI. Red Giant
• Collapsing outer layers
cause core to heat up.
• Fusion of helium into
carbon begins
• Forces regain balance
• Outer shell expands
from 1 to at least 40
million miles across. (10
to 100 times larger than
the sun)
• Red Giants last for about
100 million years

13. Unbalanced Forces (Again)
• When the Red Giant has fused all of the helium into
carbon, the forces acting on the star are again
unbalanced
• The massive outer layers of the star again rush into
the core and rebound, generating staggering
amounts of energy.
• What happens next depends on how much mass
the star has.

14. Mass Matters
Red Giant
Mass < 3 x Sun
Red Supergiant
Mass > 3 x Sun
White Dwarf
Black Dwarf Supernova
Neutron Star Black Hole

15. VII. White Dwarfs
• The pressure exerted on the core
by the outer layers DOES NOT
produce enough energy to start
carbon fusion.
• The core is now very dense and
very hot. (a tablespoon full would
weigh 5 tons!)
• The stars outer layers drift away
and become a planetary nebula
• A white dwarf is about 8,000 miles
in diameter
• After 35,000 years, the core begins
to cool.

16. VIII. Red Supergiants
• If the mass of a star is 3 times that
of our sun or greater, then the
Red Giant will become a Red
Supergiant.
• When a massive Red giant fuses
all of the helium into carbon,
fusion stops and the outer layers
collapse on the core.
• This time, there is enough mass
to get the core hot enough the
start the fusion of carbon into
iron.

17. Red Supergiants
• Once fusion
begins, the
star will
expand to
be between
10 and 1000
times larger
than our sun.

18. IX. Supernova
• When a Supergiant
fuses all of the Carbon
into Iron, there is no
more fuel left to
consume.
• The Core of the
Supergiant will then
collapse in less than a
second, causing a
massive explosion
called a supernova.
• In a supernova, a
massive shockwave is
produced that blows
away the outer layers
of the star.

19. X. Neutron Star
• Sometimes the
core will survive the
supernova
• If the surviving core
has a mass of less
than 3 solar
masses, then the
core becomes a
neutron star.

20. XI. Black Holes
• If the mass if a surviving
core is greater than 3
solar masses, then a
black hole forms
• A black hole is a core so
dense and massive that
it will generate so much
gravity that not even
light can escape it.
Since light can’t
escape a black hole,
it is hard to tell
what they look like
or how they work.

21. Lifecycle of stars
• The largest black holes in the universe
• https://www.youtube.com/watch?v=xp-8HysWkxw
• Life and Death of Stars
• https://www.youtube.com/watch?v=mzE7VZMT1z8

22. Neutron Star
Black Dwarf
Main Sequence
Nebula

23. Warm Up
• Fill in the
missing pieces 1.
2.
3.
4.
5.
6.
7.