Download Project 3: Astronomy Lesson

This guide will discuss
the life cycle of a star
(stellar evolution).
Throughout the guide,
pay attention to
highlighted words, they
may be on the quiz
Learning Environment
Students will only need a computer lab or
home desktop/laptop to complete this study
guide and quiz
Target Audience
Grades 9-12
For individual learning
Objectives
Students will learn about the life and
death of stars, and upon
completion of this study guide, be
able to identify layers of a star and
other material contained in this
study guide with 80% accuracy
Controls
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Astronomy:
The Life Cycle of Star
Table of Contents
What is Stellar Evolution?
• Stellar Evolution is the life cycle of
a star and the processes that it will
undergo throughout its life
What is a Star?
• Stars form from dense molecular clouds, also
known as GMCs (Gaseous Molecular Clouds)
• The cloud becomes so large, the force of
gravity is extremely intense
• The GMC collapses in on itself with a massive
amount of pressure (this is known as
gravitational collapse)
Gravitational Collapse?
• The collapsing gas implodes with so much
pressure, it creates a massive amount of heat
and energy (similar to more friction = more
heat)
• The core of the GMC is so hot and dense,
gravity takes over and it begins to spin
• This is called a
(like a baby star)
• The faster the protostar spins, the hotter
it becomes
• Once the internal temperature reaches
10 million Kelvins, the
begins
• At this point, the hydrogen (H) molecules
in the core begin to fuse with the helium
(He) molecules
• If the protostar‘s temperature never
begins the proton-proton reaction, it
become what is know as a brown dwarf
• Essentially this is known as a dead star
• Over hundreds of thousands of years it
will slowly cool and become dimmer and
dimmer
What is Next?
• Once the star’s internal pressure pushing outwards
equals the force of gravity pushing inwards, the star
reaches the stage known as hydrostatic equilibrium
• The outward pressure is created by more and more
molecules fusing, creating more heat
• Example: a balloon in a cold room versus a balloon in
a hot room (hot one expands more, creating more
outward pressure)
• The star then enters the
of its life
Main Sequence Stage
• Depending on the mass of the star, it can
remain a Main Sequence (M.S.) star for
an extremely long time
• Larger stars burn up their “fuel” faster,
thus remain a main sequence star for
shorter amounts of time
This the Main Sequence Chart (also known as the
Hertzsprung-Russell diagram)
• M.S. stars are placed on the
Hertzsprung-Russell Diagram
according to
and
temperature
• The brighter the star, the hotter it
is, less heat = less luminous
• Depending on the size of the star, it
may go through its life cycle and end
up as many different things
• Smaller stars become
eventually
• Larger stars can become supernovas,
black holes, or neutron stars
Choose one to explore the life cycle of that
type of star
Low Mass Star
• Stars smaller than .05
will die
when they have used up their supply of
hydrogen molecules
• Not all low mass stars become large enough to
reach the main sequence stage
• When they use all the hydrogen, they collapse in
again and create a white dwarf
A White Dwarf Star
Mid Size Stars
• Range from 1.4 solar masses to 10 solar masses
• Depending on the size of the star, it will live
longer
• Mid size stars, like our sun, can survive for
millions of years
• As a star reaches its end, the core heats rapidly
and the outer layers expand away from the core
(in effect the star begins to swell)
• The hotter the internal temperature gets, the
more force the outer layer are pushed
outward with (the bigger the star the more
force the layer are pushed out with)
• The further the layers get from the core, the
cooler they become
• Once expansion of the cooling outer layers
stops, they become a reddish color
• A star in this stage is known as a red giant
• The farther the layers get from the core,
the less gravity they have holding them to
the star
• Eventually they will get pulled off of the
star and be dispersed back into space
• This forms planetary nebulae
• Eventually, the core implodes and forms
a white dwarf
Red Giant
Planetary
Nebulae
Massive Stars
• Use the
instead of the proton-proton chain
to maintain equilibrium
• Range from 15 solar masses to 115 solar masses
(most massive, like VY Canis Major)
• They are so large, they are not usually main sequence
stars
• Smaller massive stars outer layer expand and cool just
like some main sequence stars
• Even though these stars are cooler than some smaller
stars, they are brighter (more heat = brighter star)
Sounds like a Contradiction…
• It seems incorrect that if heat creates a brighter star,
how can a cooler star be brighter?
• Example:
– Two side by side 100 watt light bulbs compared to
10 side by side 75 watt bulbs
– Less powerful bulbs, but based on pure wattage the
10 bulbs are brighter
– Massive stars are cooler, but they have so much
surface mass creating the light, they are brighter
• Massive star end their lives in one of two ways:
neutron stars or black holes
• The star is so large, when it dies the sheer mass
collapsing in on itself can turn the protons inside the
star into neutrons, forming a star made completely
of neutrons
• It the star is a large massive star, it will explode, and
then collapse in back on itself with so much force
and pressure that gravity will never take hold, and
the star will continue to collapse forever, creating a
black hole
Nuetron Stars
• Neutron stars are extremely small (in star terms)
• They are usually about 10km across, the size of a small
city
• They are super dense and spin at about 600
revolutions per second
Black Holes
• 2-3 solar masses in size
• Black holes can’t actually be seen through a regular
telescope
• Scientists can only detect them in one of 2 ways: super
nova remnant or a black hole “sucking up” matter from a
nearby star or space gas
• Before a black hole is created, it is preceded by a
supernova (major expansion just before the implosion, like
a “cosmic bomb”) that disperses the stars outer layers
(cosmic matter) back into the universe
A black hole “sucking up” cosmic matter from a nearby star
Zones of a Star
1. Corona
– atmosphere of a star”
2. Chromoshpere
– Visible during a total eclipse of a star
3. Photoshpere
– About 10,000 degrees Kelvin
– The visible layer that we “see”
4. Convection Zone
– Layer just below the surface where all the stars material is in
constant motion via convection
5. Radiation Zone
– Extremely high temperatures allow gas to be copleteley
ionized
6. Core
– Almost 17 million degrees Kelvin
– center of the star”
An Acronym to Remember
• When you are trying to remember the
different zone of a star, try to
remember these two words:
• Co/Ch/pho Con/ra/Core = Corona,
chromoshpere, photoshpere,
Convection Zone, Radiation Zone,
Core
Quiz
Table of Contents
Keywords
Home
Keywords
Protostar
• When a GMC collapses in on itself,
then stabilizes through hydrostatic
equilibrium.
• This is how a star is born, so you
could say a protostar creates a baby
star
Proton-Proton Chain
• Process of fusing hydrogen to helium
atoms at the core of a star
• Occurs in low to mid-mass stars
• What causes the stars collapse to stop
and allow it to become balanced
Main Sequence Star
• A graph (also known as the HertzsprungRussell Diagram) that plots a star based
on color and brightness
• Where a star is placed on this graph can
tell you how long it will “live” and what it
looks like to the naked eye
Luminosity
• Candela/ per Square Meter
• How bright the star actually is, not
how bright it appears to be to the
naked eye
Solar Masses
• A unit used to describe stars size
• Based on the size of our sun (1 sun =
1 solar mass)
• Example: A star of 1.9 solar masses
is 1.9 times bigger than the sun
White Dwarf
• Final evolutionary stage of a star that did
not have enough mass to become a
supernovae or neutron star
• White dwarfs are so dense they are
about the mass of the sun crammed into
a star remnant the size of the Earth!!!
CNO Cycle
• Carbon-Nitrogen-Oxygen cycle
• How massive stars obtain hydrostatic
equilibrium
• Usually occurs in stars above 3.3 solar
masses
Quiz Time!!!
You will now be quizzed over some of the
keywords and material in the study guide.
Hope you were paying attention!!
(click on the letter of the answer, not the words)
1. What is Stellar Evolution?
a. Life of a star and the processes
that it undergoes.
b. Evolution from birth to death of
the universe.
c. How a star is created.
d. The age of a star.
Correct!!!
Incorrect!!!
2. True or False?
Stars form from the
expansion of a cloud of
space dust
Correct!!!
Incorrect!!!
3. A More massive star:
a. Live longer than low-mass stars.
b. Die and Create a black hole or
neutron star.
c. Have shorter lives than main
sequence stars.
d. A and C
e. B and C
Correct!!!
Incorrect!!!
4. The order of layers of a star from
outermost to innermost is:
a. Convection, Corona, Core,
Photoshpere
b. Photoshpere, Chromoshpere,
Corona, Core
c. Corona, Chromoshpere,
Photoshpere, Convection, Radiation,
Core
d. Convection, Radiation, Photoshpere,
Chromoshpere, Corona, Core
Correct!!!
Incorrect!!!
5. Low-mass stars that “die” before
they begin the proton-proton chain
become:
a. Supergiants
b. White Dwarfs
c. Brown Dwarfs
d. Neutron Stars
Correct!!!
Incorrect!!!
Congradulations!!!
You have completed
the study guide!!!!