Download Chapter 30 Section 2 Handout

Chapter 30 Section 2
Handout
Stellar Evolution
1
Why are astronomers not able to observe
the entire life of any star?

Because a star typically exists for billions of
years.
2
What is luminosity?

The total amount of energy a star gives off
each second.
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.
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 star’s
surface.
Vertical axis: The
luminosity of a star.
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.
6
What is a nebula?

A cloud of gas and dust where a star begins.
7
What is Newton’s law
of universal
gravitation?

All objects in the
universe attract each
other through
gravitational force.
8
Gravitational force increases as the mass
of an object:

Increases or as the distance between two
objects decreases.
9
What is a protostar?

A shrinking, spinning region that begins to
flatten into a disk with a central concentration
of matter.
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.
11
What is important about the onset of
fusion?

It marks the birth of a star.
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
Life Cycle of Stars by MASS
Star like our
sun
Nebula-gas
and dust
Red
giant
Planetary
nebula
White
dwarf then
black
dwarf?
Protostars
Massive
star
Red
supergiant
supernova
Neutron
star and/or
black hole
12
What happens as gravity increases the
pressure on the matter within a star?

The rate of fusion increases.
13
What does the equilibrium between the
outward pressures of radiation and the
force of gravity do?

It makes the star stable in size.
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.
15
What is the second and longest stage in
the life of a star?

The main-sequence stage.
16
A star that has the same mass as the
sun’s mass:

Stays on the main sequence for about 10
million years.
17
When does a star enter its third stage?

When almost all of the hydrogen atoms in its
core have fused into helium atoms.
Nucleosynthesis and Fusion
Reactions
The main process responsible for the energy produced in most
main sequence stars is the proton-proton (pp) chain.
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.
Red Giant Stars
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.
20
What are supergiants?

Main-sequence stars that are more massive
than the sun and become larger than regular
giant stars.
21
What is a planetary nebula?

A cloud of gas that forms around a sunlike
star that is dying.
22
What is a white dwarf?

A hot, extremely dense core of matter leftover
from an old star.
23
What is a black dwarf?

A white dwarf that no longer gives off light.
24
An explosion on a white dwarf caused by a
pressure build-up is a:

Nova
25
What effect may a nova have on a star?

It may cause it to become many thousands of
times brighter.
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.
27
Stars that have masses of more than 8
times the sun’s mass produce supernovas:

Without needing a secondary star to fuel
them.
The End?