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The Evolution of Stars
Star Formation - Gravity
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What is gravity?
Gravity is the force that
keeps us safely planted
here on Earth, but it is
more that just that.
Gravity, or gravitation, is
the natural phenomenon by
which all objects with mass
attract other objects.
Without gravity the
universe would be a very
different place.
Gravity
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This attraction takes
place because these
objects actually bend
space, causing other
objects to be drawn
towards them.
Gravity
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This attraction occurs
between the smallest of
particles, even atoms.
Gravity
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How does this work in star formation?
Atoms of hydrogen will attract one another
because of gravity.
When enough hydrogen comes together a star
can form.
The question is where can we find that much
hydrogen.
Star Formation - Nebulae
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Nebulae are massive
dust/gas clouds that are
found throughout our
galaxy and other.
To the right is the
Witchhead Nebula and
the Horsehead Nebula.
Nebulae are sometimes
referred to as stellar
nurseries.
Nebulae
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In a nebula unimaginable
amounts of hydrogen gas
will collect because of
gravity.
All this gas causes
temperatures to rise.
When it reaches about 10
million degrees Celsius
fusion, a nuclear reaction,
takes place.
Star Formation – Stable Stars
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In order for a star to
exist it must remain
stable.
It is a balance between
gravity wanting to
draw material towards
the center and radiant
energy wanting to
move away from the
center.
Break from Note Taking
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Please open your texts
to p.468.
Types of Stars
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There are three basic groups of stars we will
look at:
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Low Mass Stars
Intermediate Mass Stars
Massive Stars
Low Mass Stars
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Low mass stars are the
longest lived stars,
existing for as long as
100 billion years.
They lose most of their
mass over this time and
end up as white dwarf
stars.
Intermediate Mass Stars
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These stars exist for about 10 billion years.
Our sun is an example of an intermediate
mass star.
It goes through its cycle of fusing hydrogen
into helium relatively quickly.
Intermediate Mass Stars
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Eventually the
hydrogen in the star
(that is being fused into
helium) will begin to
run out.
Energy production
ceases.
The star begins to
collapse in on itself
because of gravity.
Intermediate Mass Stars
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As the star collapses
the core contracts. The
outer layers expand
causing the star to
swell in size.
(Sometimes up to 100
times its original
diameter.
Intermediate Mass Stars
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As the core pressure
increases so too does
the temperature.
When it reaches 100
billion degrees Celsius
the helium in the core
begins to fuse into
carbon.
Intermediate Mass Stars
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As the star increases in
size its outer layers
decrease in
temperature, causing a
colour change to red.
Intermediate Mass Stars
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Eventually the star will
shed its outer layers of
gas, leaving a small,
white-hot core amidst a
swirling cloud of gas.
This is called a
planetary nebula.
Intermediate Mass Stars
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Over time the small
remains of the star,
called a white dwarf,
will cool eventually
becoming a dark sphere
of matter.
This black dwarf emits
no visible light.
Massive Stars
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Massive stars have the shortest life span, a
mere 7 million years.
They burn through their hydrogen very
quickly at a very high temperature.
The temperature is so hot that once the
hydrogen fuses to helium, the helium then
fuses to carbon, silicon and finally iron.
Massive Stars
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When massive stars swell
to supergiants they are near
the end of their life cycle.
The end for these stars are
cataclysmic.
The outer layers of the star
are blown away in a
massive explosion when
the iron core collapses in
on itself.
The result is a supernova.
Massive Stars
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The end for a massive star can take two
forms:
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A neutron star
A black hole
Neutron Stars
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After going nova if the
remaining core of the
star is 1.4 to 3 solar
masses a neutron star
will form.
Neutron Star
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A neutron star is a very small, extremely
dense sphere.
Its core is fluid, made up of neutrons (which
formed through the fusion of electrons and
protons).
Black Holes
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A supernova that
results in a core of 3
solar masses or greater
can form black holes or
singularity.
A black hole is an
infinitely small,
infinitely dense
remnant of a supergiant
star.
Black Holes
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The gravity is so great
in a black hole that
even the light that it
emits cannot escape it.
Hence the term black
hole.
Black Holes
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Objects that stray too
close to a black hole
and get caught in its
gravity undergo a
process called
spagettification.
The object is torn apart
right down to the
atomic level.
Homework
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Please finish reading section 14.2, pages 468-473.
Complete the investigation activity on p.472, completing
questions 1-5.
Complete questions 1-6 on p.473.
Vocabulary
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Fusion
White Dwarf
Black Dwarf
Planetary Nebulae
Supernova
Neutron Star
Black Hole