Sample student product on the evolution of a star.

1. Noor Hussain Pyarali
The Evolution of a Star

2. How to Navigate
Below are the buttons that are on every screen.
Click on the buttons to navigate.
A click on this button
will take you home, no
matter what page you
are on.
A click on this button
will take you to the end.
A click on this button
will take you to the
previous page.
A click on this button will
take you to the next page.
How To Overview HRD Stars
Guided
Practice
Quiz ResourcesMain

3. All about Stars: Overview
Today you will be learning about the life cycle of a star through
its different stages of development.
Nebula
Nebulae consist of
clouds of dust and
gas. This is where
all stars are born.
Stars
Stars are massive
balls of gas that
give off light and
heat. Stars can live
for billions of years.
The Death of a Star
When stars die they
become either
neutron stars, black
holes, or white
dwarfs.
Transition
A supernova
explosion or a
planetary nebula
are what happens
to a star before it
dies.
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

4. Overview
You will also learn how to classify stars!
In order to better understand the life
cycle of a star and the different stages
they go through, it is important to
understand how they are classified.
Stars are classified based on their
temperatures, luminosity (absolute
magnitude), color, and size.
White dwarf
Nebula
The Sun
Black hole
The Andromeda Galaxy
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

5. Hertzsprung-Russell Diagram
All stars are different! Some are just beginning their, forming in a
nebula. Some are middle-aged, enjoying the long life of a main
sequence star, and some have begun to die. The Hertzsprung-
Russell (HR) Diagram is a tool that allows us to examine the
relationships between stars. It is like family portrait in a sense. The
HR diagram shows stars of different ages and different stages, all at
the same point in time.
On the HR diagram, each star is represented by a dot.
The position of each dot tell us two things about a star: its
luminosity (absolute magnitude) and its temperature. The vertical
axis represents a star’s luminosity. Luminosity is the amount of
energy radiated per second, but you can also think of it as how
bright or dim a star appears. All stars on this scale are compared to
each other based on a reference – our sun! The horizontal axis
represents the star’s surface temperature (not core temperature).
This labeled using the Kelvin temperature scale. On the next page
you will learn more about the Kelvin scale!
O B A F G K M OBAFGKM in the HR Diagram
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

6. Condition oF oC oK
Water boils 212 100 373
Room
Temperature
72 23 296
Water Freezes 32 0 273
Absolute Zero -460 -273 0
Kelvin
Kelvin is a
measure of
temperature,
like Fahrenheit
and Celsius
Kelvin (oK) is the measure of temperature that astronomers use to
describe how hot stars and other celestial objects are. When
Celsius is at 0, you can see that Kelvin (K) is at 273 degrees. On a
night when its snowing outside and the temperature is 32 oF, you
can tell your friends that it is 273 degrees outside! Degrees Kelvin,
that is!
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

7. Class Temperature Star Color
O 30,000 - 60,000 °K Blue
B 10,000 - 30,000 °K Light Blue
A 7,500 - 10,000 °K White
F 6,000 - 7,500 °K White (yellowish)
G 5,000 - 6,000 °K Yellow (like the Sun)
K 3,500 - 5,000 °K Orange
M 2,000 - 3,500 °K Red
Most stars are classified by their characteristics into a spectral class. The spectral classifications are
OBAFGKM. The traditional mnemonic for remembering the spectral types are “Oh Be A Fine
Guy/Girl Kiss Me.” The hottest stars are an O class and the coolest stars are a M class. The spectral
types are enhanced by numbers 0 through , with a 0 indicating a hotter star and a 9 indicating a
cooler star in a spectral class. For example, an A5 is five tenths away from a B0 and a F0. An A2
star would be hotter than an A8 star. Our sun is a G2, which is fairly hot for a G class. Below is a
chart that will help you see the differences between the classes in degrees Kelvin.
Main How To HRDOverview Stars
Guided
Practice
Quiz Resources

8. Now that you’ve learned all about the HR diagram, the Kelvin scale, and the spectral class its time to
focus more specifically on the life cycle of stars. Stars form in the nebulae, become average, main
sequence or a massive stars, go through a transition of either a supernova or planetary nebula, then
die as a white dwarf, neutron star or a black hole.
This can also be a
Blue Supergiant.
Black dwarf
A white dwarf that has
cooled down enough
that it no longer emits
light. This remains a
theory for now, since
the universe is none
have been observed.
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

9. All stars are formed out of nebulae (nebula, singular). There are 5 main types of nebulae: Emission, Reflection, Dark, Planetary, and
Supernova Remnant. Nebulae consist of dust, gas, and other materials. Inside of nebulae things can be pretty quite and calm – until
a star or other celestial body passes by. This stirs things up! Swirls and ripples spread throughout, due to the gravity of the celestial
body that passes either through the nebula or nearby it. Piles of matter build, forming gigantic clumps of dust and gas. The clumps
of dust and gas, called protostars, become larger. As they become larger, gravity squeezes them tighter. Pressure builds and heat
increases. A star is formed! Now let’s take a look at the different types of nebulae.
Emission Nebulae are clouds of
high temperature gases that
have an abundance of hydrogen.
This is the most colorful of the 5
types, but usually appear to have
a lot of red due to the amounts
of hydrogen.
Reflection Nebulae
are clouds of dust
that reflect the light
of nearby stars.
They normally
appear blue.
Dark Nebulae are
clouds of dust that
block the light of
whatever is behind it.
They are physically
very similar to
Reflection Nebulae.
Planetary Nebula are
created when a star
nearing the end of its
life casts off its outer
layers.
Supernova Remnants are
created when a massive
star explodes near the end
of its life. This blows a
large portion of the star
(gas) through space. The
Crab Nebula is a well-
known example, created by
a supernova.
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

10. You have learned about nebulae, where stars are formed. Now you will learn about main sequence stars, average stars. The
majority of stars in the sky are main sequence stars. Our Sun a G2 star, Sirius A an A1 star, and Bellatrix B2 are main sequence
stars. You have already learned about the HR Diagram. Let’s have another look with closer attention on just the main sequence
stars.
Main sequence stars have a vast range in luminosity, color, temperature, and size as you can see in the diagram. They are the ones
that seem to group together in a diagonal line. They can be the larger, more luminous blue stars that burn hot and bright, seen at
the top left. They can be the average sized yellow, yellow-orange stars, like our sun. Or, they can be the smaller, cooler red dwarf
stars, seen at the bottom right.
Stars convert hydrogen into helium through nuclear fusion, releasing energy that radiates out while gravity pushes in.
You may imagine that a more massive star in the main sequence would live a longer life because it would have more fuel at its core
to burn. That would be wrong - the opposite it true! The more massive blue stars at the upper left have a stronger gravitational
force pushing inwards so their cores get hotter. Higher temperatures mean nuclear reactions occur at a much greater rate. Thus,
they use up their fuel much quicker than lower mass stars, such as red dwarfs. A star with only half the mass of the sun can spend
80 billion years in main sequence, while the sun will spend approximately 10 billion.
Sirius A
Bellatrix
Main How To Overview HRD Stars Quiz
Guided
Practice
Resources

11. Giants and Supergiants! Oh my! Giant stars are more massive and more luminous than main sequence stars, even though they may
have around the same surface temperature. Giants, therefore, are above the main sequence in the HR diagram.
Pollux
Arcturus
Aldebaran
Pollux once was a type A main sequence star. It has since
exhausted the hydrogen from its core and evolved into a giant
star. It is now a K0 star with a surface temperature of about
4,600 oK. Arcturus is a K1 orange-red giant, 4,300 oK, and
Aldebaran is a K5 red giant, 4,010 oK. Giant stars evolved from
main sequence stars. They are older stars that have burned their
hydrogen cores.
Giant stars evolve from main sequence stars A,F,G,K,M. Supergiants
evolve from massive O and B type stars. Just like giant stars,
Supergiants are older stars that have burned their hydrogen cores. Due
to their extreme masses, O and B spectral classes have the shortest life
spans of about 30 million years. Betelgeuse and Antares are both red
supergiants. Betelgeuse is a M2, 3,500 oK. Antares is a M1 and is about
3,400 oK. Rigel is a blue supergiant; it is a B8 with a surface
temperature of about 11,000 oK. Deneb is a blue-white supergiant, that
was probably an O star during its main sequence life.
Deneb
Rigel
Betelgeuse
Antares
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

12. A supernova is an energetic explosive event, which occurs at the end of a stars lifetime. The reason this occurs at
the end of a supergiant’s lifetime is because its nuclear fuel becomes exhausted and the star is no longer supported
by the release of nuclear energy. After the supernova explosion, it blasts its outer layer into space. These outer
layers are called supernova remnants, which you’ve read about already  But, what happens to the rest of the star
that has not been blasted into space? It becomes either a neutron star or a black hole.
Giant stars do not explode as a supernova, like the
supergiant stars, but they do go through a process of
change at the end of their lives. This change is called
Planetary Nebula. When this occurs the outer layers of
the star are expelled through strong stellar winds.
What remains of the star becomes a white dwarf.
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

13. A neutron star is what
may develop at the end of
a supergiant’s life, after
the event of a supernova.
It is the stellar remnant
of a supergiant.
A white dwarf is what our sun
will eventually become one
day, after about 10 billion
years. The are the stellar
remnants of giant stars.
Black holes are dense, matter-packed small areas with a
gravitational force so strong that nothing, not even light,
can escape. A supergiant’s death can be a black hole’s
beginning.
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

14. Guided Practice
1. Describe the surface temperatures and color:
A. a hot O2 star
B. a cool M3 dwarf
C. a G2 star like our sun
2. What is the spectral type of star with:
A. a surface temperature of 10,000 K
B. a surface temperature of 5,000 K
3. What is the color of a star with:
A. a spectral class A0
B. a surface temperature of 4,000 K
4. All stars form in a _____________.
5. Pollux, a red giant, was once a _________ star.
6. When a supergiant gets older and uses up its fuel,
it explodes as a ___________.
7. After going through supernova, the star will die
out as a ___________ or a ___________.
8. A red giant star will expel its outer layer in an
event called ___________.
9. A red giant star will eventually die out as a
_________.
Click on this button to go back to the section and find the
answers for questions 1-3.
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

15. Quiz
True or False
1. Kelvin is a measurement of temperature.
2. An O class star has a cooler surface temperature than a K class star.
3. An average sized star will eventually become a red giant.
4. A massive O, B class star will eventually become a supergiant.
5. After going through a supernova, the remains of the star will become a white dwarf.
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

16. Answers to Quiz
1. It is true that Kelvin is a measure of temperature. Astronomers use Kelvin for celestial objects.
2. This is false because an O class star is hotter than a K class star. O class stars are the hottest. M class
stars are the coolest.
3. It is true that an average sized star will become a red giant. Main sequences stars A-M will all eventually
become red giants.
4. It is true that both O and B stars will become supergiants, because O and B stars are massive.
5. This is false. After a star goes through supernova it will become either a neutron star or a black hole. It
will not become a white dwarf.
Congratulations!! You have completed the lesson on the life cycle of stars!!
Main How To Overview HRD Stars
Guided
Practice
Quiz Resources

17. Resources
1. National Aeronautics and Space Administration. NASA.
nasa.gov
2. Astrophysics and Astronomy. Instituto Scientia
astrophysical.org
Home How To Overview HRD Stars
Guided
Practice
Quiz Resources