Download The Life Cycle of a Star

The Life Cycle of a Star
A Really “Hot” Topic
By Samantha Edgington
Objectives
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Describe how stars are formed.
Explain the concept of equilibrium.
Define the “death” of a star.
Identify the different types of stars.
Describe how the process
of nuclear fusion works
within a star.
What is a Nebula?
• A nebula can be defined as a
thinly spread cloud of interstellar
gas and dust.
• Some nebulae are the remains of
a supernova explosion.
– the death and collapse of a massive
star can cause this explosion, this
means nebulae can be the remains
of old, dead stars.
• Most nebulae are gravity-induced
condensations of gases where
protostars are born.
How is a Protostar Formed?
• Inside a nebula, there are areas where
gravity causes dust and gas to “clump”
together.
• As these “clumps” gather more and more
mass their gravitational pull increases,
forcing more atoms together.
• This process is known as accretion, and
the result is a protostar.
How does a Protostar Become
a Star?
• In order to comprehend this
process, the concept of
equilibrium must be
understood.
• Equilibrium is in essence a
balance.
• In the case of star formation
this balance exists between
gravity and gas pressure.
Achieving Equilibrium
• First gravity pulls gas and dust inward
towards the core of the prospective star.
• Inside the core, density and temperature
increases as atomic collisions increase,
causing a rise in gas pressure.
• Finally when gas pressure is equal
to gravity, the protostar has reached
equilibrium and is therefore reached a
reasonably stable size.
The Birth
• Once the protostar
has achieved
equilibrium one of two
things occur:
 If there is not a
sufficient mass, it
becomes a brown dwarf
which is a “star” that
doesn’t radiate much
heat and light.
 In the event it does
contain an appropriate
amount of matter,
nuclear fusion begins
and light is emitted.
The Main Sequence
• A star is basically a huge ball of gas
undergoing nuclear fusion.
• The main sequence phase is where stars
spend the majority of their “life” by fusing
hydrogen into helium.
• There are two types of main
sequence stars:
 a red giant which is a large bright
star with a cool surface.
 a red dwarf which are very cool, faint
and small stars
The Ending of Main Sequence
• The star slowly shrinks over
billions of years as the
hydrogen is used by fusion.
• The star’s temperature, density,
and pressure at the core
continues to increase.
• Once the hydrogen is depleted,
the helium is fused into carbon,
when this occurs the star has
reached “old age”.
The Death
• There are one of two ways a star can die
depending on its size.
• If the star is of low mass, it expands its
outer layers, creating nebulae and a white
dwarf forms from the core.
• If it is of high mass, death occurs in a
massive explosion known as a supernova,
the remaining core then transforms into a
neutron star or a black hole.
What is a White Dwarf?
• They form from the core of a dead red giants
that were too small to fuse carbon.
• Since they do not undergo fusion,
they have no energy source and
gradually fade.
• When they radiate away all of
their energy they will theoretically
become a black dwarf.
• Since white dwarfs cannot be
older than the universe (13.7 billion years) no
black dwarfs are currently in existence.
What is a Supernova?
• They can form when the gravitational potential
energy—created by a sudden gravitational
collapse of a large red giant—heats and expels
the star's outer layers, resulting in an explosion.
• Also, they can form when a white dwarf ignites
carbon fusion, which results in a runaway
nuclear fusion reaction and causes a supernova.
• Supernovae can be so immense that the energy
produced can equal the energy the Sun creates
over a time period of 10 billion years!
What is a Neutron Star?
• A neutron star is formed as a result of a massive
star being compressed.
• The core material, known as neutron degenerate
matter, mostly consists of neutrons with a few
protons and electrons.
• The gravity is so intense that if an object were to
reach the surface it would disperse all of its
subatomic particles and merge with the star!
• The matter is so dense that a teaspoon would
weigh billions of tonnes!
• Some people view neutron stars as giant atoms.
What is a Stellar Black Hole?
• If a collapsing star exceeds
the maximum mass a
neutron star can be it will
develop into a stellar black
hole.
• Black holes are extremely
dense areas with a
gravitational pull so powerful
not even light can escape!
• What could be a reason why
black holes are black?
Chart of the Stars
Star Type
Solar Mass
Temperature (K)
Color
Red Giant
10 - 15
2,500 - 3,500
orange - red
Red Dwarf
0.1 - 0.5
2,500 – 3,500
red
Blue Giant
10 - 15
~30,000
blue - white
Brown Dwarf
0.013 - 0.084
~1,000
red
Yellow Dwarf
0.8 -1
5,300 - 6,000
white - yellow
White Dwarf
< 1.4
4,000 - 150,000
white
Neutron Star
1.4 - 3
~1,000,000
blue
The Sun’s Life
• Now that a basic
overview of a star’s
life cycle has been
covered, the
details of the most
important star’s life
can be revealed.
• Can you guess
what type of star
the Sun is?
The Sun in Main Sequence
• The Sun was born like any other star, out
of a nebulae and into a protostar.
• It is now in its main sequence and can be
classified as a yellow dwarf.
• The Star is about 4.57 billion years old,
about halfway through its complete
lifecycle.
The Sun’s Death
• Since the Sun is considerably smaller it
will not explode in a supernova.
• Instead it is predicted that it will become a
red giant in about ~6 billion years.
• When this occurs, all the water on earth
will be vaporized and life will cease to
exist.
• In the final phase the Sun will form a white
dwarf and slowly fade out of existence.
Works Cited
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www.dictionary.com
aspire.cosmicray.org/labs/star_life/starlife_proto.html
www.astro.keele.ac.uk/workx/starlife/StarpageS_26M.html
http://www.telescope.org/pparc/res8.html
www.antonine-education.co.uk
www.darkstar1.co.uk
www.pbs.org
outreach.jach.hawaii.edu
www.spaceflightnow.com
wikipedia.org
• www.cosmographica.com