Download The Life of a Star

The Life of a Star
(15.1)
BLM 15.1b
The Life of a Star (p. 468)
We say that stars have a “life” because
they form from clouds of gas and dust
and follow a predictable series of
stages:

they begin (“birth”)

they develop

they end (“die”).
Each life might take billions of years or
more.
Three types of Stars
There are three types of stars:
Dwarf (same or less mass than the sun) - 95%
The sun is actually a dwarf.
Giant (10 times the mass of the sun) – 4%
Supergiant (30 times the mass of the sun) – 1%
Birth
All stars begin their lives as nebulas,
which are huge clouds of dust and
gases, mainly hydrogen and helium.
As they swirl around, the dust bumps
into each other and forms larger
and larger clumps.
Early Life
When clumps have enough hydrogen
and dust – nuclear fusion starts.
They have become new stars.
They get hotter and hotter from
the nuclear fusion.
You would think that the larger a
star is the longer it would live,
this is not true.
Life of Stars
Dwarf stars undergo nuclear fusion for
about 10 billion to 100 billion years. (not
bright at all)
Giant stars produce energy for a few million
years. (5000x’s as bright as the Sun)
Supergiant stars produce energy for about
a million years. (extremely bright)
Giant and Supergiant stars use their energy
faster. This is why they are brighter and
don’t last as long.
Old Age
When a star nears the end of its life it
starts to use the last of it’s hydrogen
fuel and swell slightly larger as pressure
reduces and turns red (cools down).
Supernova
A supernova is an enormous final explosion
of a star as it uses up the last of it’s
fuel.
The center of the star collapses inward
to become either a neutron star or a
black hole.
The outer layers of the star explode and
the gas and dust are pushed outwards.
What is left?
Dwarf stars - cool and fade away.
Giant stars - the core packs together as a
neutron star. An extremely dense star
composed of neutrons.
Supergiant stars - the core packs together
as a black hole. A small, very dense object
with a force of gravity so strong that
nothing can escape from it. Even light
cannot get away from its surface so they
can exist undetected.
Summary
See page 469 in
your text.
Summary
Dwarfs
Same size as Sun
Giants
Supergiants
10 times mass of Sun 30 times mass of Sun
95%
4%
1%
From sm. Nebula
From med. Nebula
From very lg. Nebula
in heat and size
in heat and size
in heat and size
Last 10-100 billion yr
Lasts 3-5 million yr
Lasts 1 million years
Not very bright
Bright
very bright
Gases drift away
Core collapses
Core collapses
Fades away
Neutron star created
Black hole created
Questions p. 471
1. Describe how a star forms.
Stars form from huge clouds of dust
and gases called nebulas. The dust
and gases swirl around, forming
clumps. These clumps attract each
other because of gravity and grow
larger and larger. When they are
large and dense enough, they begin to
produce large amounts of light energy
and other forms of energy.
Questions p. 471
2. Describe the differences between the
life of a low-mass star and that of a
star 10 times the Sun’s mass.
Low-mass stars cool down and swell up
into a red giant. Outer layers drift away
and the star shrinks to become a white
dwarf which will cool and fade away.
High-mass stars swells into a red
supergiant which undergoes a supernova.
This leaves behind either a neutron star
or a black hole depending on the mass of
the original star.
Questions p. 471
3. What is a supernova?
A supernova is a type of explosion that
occurs when the source of energy of a
high-mass star is used up. The outer
layers of the star expand outward
rapidly.
Test Review Questions
Ch.13: 13.1, 13.3, 13.4
p. 434-435: Questions 7, 11.
Ch. 14: 14.7, 14.10, 14.11
p. 464-465: Questions 3a, 8-10, 11-14.
Ch.15: 15.1
p. 484-485: Questions 2-4, 6-8.
Topics by section:
13.1: Basic Terms, How planet’s move, Key differences
between planets and stars.
13.3: Rotation vs. Revolution, How does this relate to
the Earth’s days, years, seasons.
13.4: Constellations – know how to locate on a star map.
14.7: Composition of the Sun, Parts of the Sun, How the
Sun’s energy is made.
*14.10: 5 key characteristics of the Sun: Colour, Size,
Temperature, Brightness, and Spectrum.
14.11: 4 Types of Galaxies, Which is ours?
*15.1: Stages of the life of a star, Know a little about
each stage.