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## Chapter 30 Section 2 Handout

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### Chapter 30 Section 2 Handout Stellar Evolution – PowerPoint PPT presentation

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Title: Chapter 30 Section 2 Handout

1
Chapter 30 Section 2 Handout
• Stellar Evolution

2
1
• Why are astronomers not able to observe the
entire life of any star?
• Because a star typically exists for billions of
years.

3
2
• What is luminosity?
• The total amount of energy a star gives off each
second.

4
3
• What is the Hertzsprung-Russell diagram?
• The graph that illustrates the pattern revealed
when the surface temperatures of stars are
plotted against their luminosity.

5
4
• What is plotted on the horizontal axis and the
vertical axis of the Hertzsprung-Russell (H-R)
diagram?
• Horizontal axis The temperature of a stars
surface.
• Vertical axis The luminosity of a star.

6
5
• What is the main sequence?
• The band that runs diagonally through the
Hertzsprung-Russell diagram and extends from
cool, dim, red stars at the lower right to hot,
bright, blue stars at the upper left.

7
6
• What is a nebula?
• A cloud of gas and dust where a star begins.

8
7
• What is Newtons law of universal gravitation?
• All objects in the universe attract each other
through gravitational force.

9
8
• Gravitational force increases as the mass of an
object
• Increases or as the distance between two objects
decreases.

10
9
• What is a protostar?
• A shrinking, spinning region that begins to
flatten into a disk with a central concentration
of matter.

11
10
• What happens as more matter is pulled into a
protostar?
• Gravitational energy is converted into heat
energy, and the temperature of the protostar
increases.

12
11
• What is important about the onset of fusion?
• It marks the birth of a star.

13
Life Cycles of Stars
• Stars are born (nebular theory)
• They all start like our sun converting hydrogen
into helium by high temperature and nuclear fusion

14
Life Cycle of Stars by MASS
White dwarf then black dwarf?
Star like our sun
Red giant
Planetary nebula
Nebula-gas and dust
Protostars
Neutron star and/or black hole
supernova
Red supergiant
Massive star
15
12
• What happens as gravity increases the pressure on
the matter within a star?
• The rate of fusion increases.

16
13
• What does the equilibrium between the outward
pressures of radiation and the force of gravity
do?
• It makes the star stable in size.

17
14
• How long does a main sequence star maintain a
stable size?
• As long as it has an ample supply of hydrogen to
fuse into helium.

18
15
• What is the second and longest stage in the life
of a star?
• The main-sequence stage.

19
16
• A star that has the same mass as the suns mass
• Stays on the main sequence for about 10 million
years.

20
17
• When does a star enter its third stage?
• When almost all of the hydrogen atoms in its core
have fused into helium atoms.

21
Nucleosynthesis and Fusion Reactions
The main process responsible for the energy
produced in most main sequence stars is the
proton-proton (pp) chain.
22
18
• What does increased temperature from contraction
in the core cause the helium core to do?
• As the helium core becomes hotter, it transfers
energy into a thin shell of hydrogen surrounding
the core.

23
Red Giant Stars
24
19
• Describe the stars known as giants and their
place on the H-R diagram.
• They are large, red stars whose hot core has used
most of its hydrogen.
• They are above the main sequence.

25
20
• What are supergiants?
• Main-sequence stars that are more massive than
the sun and become larger than regular giant
stars.

26
21
• What is a planetary nebula?
• A cloud of gas that forms around a sunlike star
that is dying.

27
22
• What is a white dwarf?
• A hot, extremely dense core of matter leftover
from an old star.

28
23
• What is a black dwarf?
• A white dwarf that no longer gives off light.

29
24
• An explosion on a white dwarf caused by a
pressure build-up is a
• Nova

30
25
• What effect may a nova have on a star?
• It may cause it to become many thousands of times
brighter.

31
26
• Describe a supernova and how it differs from a
nova.
• A supernova is a star that has such a tremendous
explosion that it blows itself apart.
• Unlike a nova, a white dwarf can sometimes
accumulate so much mass on its surface that
gravity overwhelms the outward pressure.
• The star collapses and is so dense that the outer
layers rebound and explode.

32
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33
27
• Stars that have masses of more than 8 times the
suns mass produce supernovas
• Without needing a secondary star to fuel them.

34
The End?