Lesson 3 | Evolution of Stars



Lesson 3 | Evolution of Stars

|Student Labs and Activities |Page |Appropriate For: |

|Launch Lab |47 |all students |

|Content Vocabulary |48 |all students |

|Lesson Outline |49 |all students |

|MiniLab |51 |all students |

|Content Practice A |52 |[pic] |

|Content Practice B |53 | [pic] |

|School to Home |54 |all students |

|Key Concept Builders |55 |[pic] |

|Enrichment |59 |all students |

|Challenge |60 | [pic] |

|Skill Practice |61 |all students |

|Assessment | | |

|Lesson Quiz A |63 |[pic] |

|Lesson Quiz B |64 | [pic] |

| | | |

| | | |

|[pic] |Approaching Level |[pic] |On Level |[pic] |Beyond Level |[pic] |English-Language Learner |

Teacher evaluation will determine which activities to use or modify to meet any student’s proficiency level.

46 Stars and Galaxies

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LESSON 3: 15 minutes

How can you identify fruits?

Flowering plants grow from seeds that they produce. Animals depend on flowering plants

for food. The function of the fruit is to disperse the seeds for plant reproduction.

Procedure

1. Read and complete a lab safety form.

2. Make a two-column table in your

Science Journal. Label the columns

Fruits and Not Fruits.

3. Examine a collection of food items.

Determine whether each item is a fruit.

Record your observations in your table.

4. Place each food item on a piece of

plastic wrap. Use a plastic or

paring knife to cut the items in half.

5. Examine the inside of each food item.

Record your observations.

Think About This

1. What observations did you make about the insides of the food items? Would you

reclassify any food item based on your observations? Explain.

2. How can the number of seeds or how they are placed in the fruit help with seed

dispersal?

3. Key Concept What role do you think a fruit has in a flowering plant’s

reproduction?

Stars and Galaxies 45

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LESSON 3

Evolution of Stars

Directions: Each of the sentences below is false. Make the sentence true by replacing the underlined word(s) with

a term from the list below. Write your changes on the lines provided. NOTE: You may need to change a term to its

plural form.

|black hole |nebula |neutron |

|neutron star |supernova |white dwarf |

1. Stars form deep inside black holes, which are clouds of gas

and dust.

2. When a star that no longer contains helium casts off its

gases, its core turns into a hot, dense, slowly cooling sphere

of carbon called a neutron star.

3. A supernova occurs when gravity is so great that no light

can escape.

4. Neutron stars contain a dense core of nebulae, which

are particles in the nucleus of an atom.

5. A white dwarf is an enormous explosion that destroys

a star.

6. A black hole is a dense core of neutrons that remains after

a supernova.

48 Stars and Galaxies

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LESSON 3

Evolution of Stars

A. Life Cycle of a Star

1. Stars have , meaning that they are born and, after

millions or billions of years, they .

2. Stars form inside a(n) , which is a cloud of gas and dust.

a. causes the densest parts of a star-forming nebula to

collapse, forming a region called a(n).

b. As they contract, protostars produce enormous amounts

of

3. A developing gets increasingly hotter over many

thousands of years, heating up the surrounding gas

and

a. The heated and dust eventually blow away, and

the becomes a visible . .

b. The gas and dust might later become or other objects

that the star.

4. A stars spends most of its life cycle on the of the

Hertzsprung-Russell diagram.

a. When a star starts hydrogen into

, it becomes a(n) star

and remains there as it continues fusing into helium.

b. A star leaves the main sequence when its supply of

has been nearly used up.

c. A massive star goes through a cycle near the end of its life in which it becomes

a(n) several times

B. End of a Star

1. All stars in the same way, but stars

in different ways.

2. -mass stars such as the Sun do not have enough mass to

fuse elements heavier than .

Stars and Galaxies 49

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Lesson Outline continued

3. Astronomers think that any star with a mass less than 10 times the mass of the

Sun will eventually become a(n) .

4. Stars that have a mass more than 10 times that of the Sun become a(n)

, which is an enormous explosion that destroys the star

at its center.

5. During a(n) , the collapse is so violent that the normal

spaces inside atoms are eliminated and a(n) star forms.

6. Massive stars have a force of that is so strong that the

matter gets crushed into a(n) .

C. Recycling Matter

1. The gas that give off at the

of their life cycles gets recycled; it is the material that forms new stars

and .

2. A(n) casts off hydrogen and helium, which becomes

part of a planetary ; these gases can form new

, not new , despite the

nebula’s name.

3. A(n) produces a shock wave that pushes on the gas

and in space.

a. Almost all the elements that are than hydrogen and

helium, including carbon, silicon, and oxygen, were released into the

universe by

b. The force of causes in

nebulae to clump together and eventually form new

and planets.

50 Stars and Galaxies

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LESSON 3: 15 minutes

How do astronomers detect black holes?

The only way astronomers can detect black holes is by studying the movement of objects

nearby. How do black holes affect nearby objects?

Procedure

1. Read and complete a lab safety form.

2. With a partner, make two stacks of

books of equal height about 25 cm

apart. Place a piece of thin cardboard

on top of the books.

3. Spread some staples over the

cardboard. Hold a magnet under the

cardboard. Observe what happens to

the staples.

4. While one student holds the magnet

in place beneath the cardboard, the

other student gently rolls a small

magnetic marble across the

cardboard. Repeat several times,

rolling the marble in different

pathways. Record your observations

in the Data and Observations section

below.

Data and Observations

Analyze and Conclude

1. Infer What did the pull of the magnet represent?

2. Cause and Effect How did the magnet affect the staples and the movement of the

marble?

3. Key Concept How do black holes affect nearby objects?

Stars and Galaxies 51

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LESSON 3

Evolution of Stars

Directions: On each line, write the term from the word bank that correctly completes each sentence. Some terms may be used more than once or not at all.

black hole fusion gravity massive star

nebula neutron star protostar red giant

star Sun supergiants supernova

white dwarf

1. A star forms deep inside a cloud of gas and dust called a .

2. causes the densest parts of the nebula to collapse.

3. A is formed and continues to contract.

4. The core of the protostar becomes hot and dense enough for

nuclear .

5. Eventually the surrounding gas and dust blows away and a

becomes visible.

6. Low-mass stars such as the Sun do not have enough mass to

become .

7. A turns into a red giant, a larger red giant, and then a red

supergiant.

8. After a low-mass star runs out of helium, the core is exposed and becomes

a .

9. When the Sun in our solar system runs out of fuel, it will become a

and then eventually a white dwarf.

10. A massive star does not become a . Instead it explodes.

11. A is an enormous explosion that destroys a star.

52 Stars and Galaxies

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LESSON 3

Evolution of Stars

Directions: Answer each question or respond to each statement on the lines provided.

1. What is a nebula, and how is it related to the formation of a star?

2. How does a protostar become a star?

3. How long does a star remain on the main sequence of the Hertzsprung-Russell diagram?

4. How does the mass of a star relate to the time it stays on the Hertzsprung-Russell diagram?

5. What steps does a massive star go through to become a red supergiant?

6. Describe the final stages of the Sun.

7. What happens to stars with more than 10 times the mass of the Sun?

8. What happens to the gas that escapes into space at the end of a star’s life cycle?

Stars and Galaxies 53

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LESSON 3

Evolution of Stars

Directions: Use your textbook to complete the activity.

For this activity, you will need one sheet of construction paper in each of several colors, such

as black, yellow, orange, red, and white. You will also need scissors, glue, and a compass for

drawing circles.

1. Review the information in your book about the Sun’s life cycle. List the stages of the

Sun’s life cycle here, in the correct order.

2. You will use the sheets of construction paper to make a time line of the various stages

in the Sun’s life cycle. The black sheet of paper will represent space. Use the compass to

make the Sun in various sizes depending on its stage. Choose appropriate colors as well.

For example, the main sequence Sun of today would be yellow. The Sun as a red giant

would be red and larger than the yellow sun.

3. Carefully cut out the Suns and arrange them in order on the sheet of black construction

paper. When you are satisfied with your arrangement, glue the Suns in place.

4. Describe the life cycle of the Sun, using your time line.

54 Stars and Galaxies

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LESSON 3

Evolution of Stars

Key Concept How do stars form?

Directions: On the line before each statement, write T if the statement is true or F if the statement is false. If the

statement is false, change the underlined word(s) to make it t rue. Write your changes on the lines provided.

1. The cloud of gas and dust in which a star forms is called a galaxy.

2 The way in which a star forms does not depend on its mass.

3. Protostars form when gravity causes dense parts of star-forming nebulae to

expand.

4. Protostars contract until their cores are cold and dense enough for nuclear

fusion.

5. A nebula glows brightly during the star-forming process.

6. The gas and dust that blow away from a protostar might later become planets

or other satellites.

7. All stars form in the same way. But stars die in different ways, depending on

their luminosity.

8. Star-forming nebulae are cold, dense, and dark.

9. A protostar that is contracting produces enormous amounts of internal energy.

10. A protostar becomes invisible when the gas and dust that surrounds it blows

away.

11. A star becomes a main-sequence star on the Hertzsprung-Russell diagram when

it begins to fuse hydrogen into helium.

12. The time that a star stays on the perimeter of the Hertzsprung-Russell diagram

depends on its mass.

Stars and Galaxies 55

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LESSON 3

Evolution of Stars

Key Concept How does a star’s mass affect its evolution?

Directions: Number the events in each chart from 1 to 5 to show the sequence in the life of each type of star.

| |Medium Mass |

| |red giant star |

| |star-forming nebula |

| |dead star |

| |medium-mass protostar |

| |white dwarf |

| |High Mass |

| |massive protostar |

| |red supergiant |

| |formation of a neutron star or a black hole |

| |star-forming nebula |

| |explodes as a supernova |

Directions: Circle the term in parentheses that correctly completes each sentence.

1. Lower-mass stars such as the Sun do not have enough (hydrogen, mass) to become

supergiants.

2. High-mass stars collapse and explode as (protostars, supernovae).

3. A lower-mass star becomes a (white dwarf, black hole) instead of a supernova.

4. A supernova destroys a massive star and leaves behind a (red giant, neutron star).

5. A neutron star collapses into a black hole because of the force of (fusion, gravity).

56 Stars and Galaxies

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LESSON 3

Evolution of Stars

Key Concept How does a star’s mass affect its evolution?

Directions: Complete each concept map by writing the correct phrase from the list in the space provided.

• can become a black hole

• can become a neutron star

• collapses and explodes

• dies more slowly

• experiences a supernova

• first becomes a red giant

• ends up a white dwarf

Stars and Galaxies 57

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LESSON 3

Evolution of Stars

Key Concept How is star matter recycled in space?

Directions: On each line, write the term from the word bank that correctly completes each sentence. Some terms

may be used more than once or not at all.

core black holes gravity

hydrogen nuclear fusion planetary nebula

planets remnant space

stars supernova white dwarf

1. When a star becomes a , it casts off hydrogen and helium

gases in its outer layers.

2. Much of a star’s gas escapes into at the end of its life cycle.

3. A is the expanding matter cast off by a star that is becoming

a white dwarf.

4. Originally, astronomers thought planetary nebulae were regions where

were forming.

5. The gases in a planetary nebula can be used to form new .

6. A supernova releases an expanding cloud of dust and gas called a

supernova .

7. Almost all elements other than hydrogen and helium were formed during

explosions.

8. The intense heat during a supernova explosion causes iron elements in the

to fuse together and form new elements.

9. Gases and other matter from planetary nebulae and

remnants can come together to form new stars and planets.

10. is the force that causes new stars to form from recycled gases

and other materials.

58 Stars and Galaxies

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LESSON 3

Into the Darkness

Scientists describe a black hole as a

collection of matter with a gravitational

pull that is so strong that nothing, not

even light, can escape from it. In the 1700s,

researchers used Newton’s ideas about

gravity to reach the conclusion that some

stars might be so big that light could never

escape from them. Then, Einstein’s general

theory of relativity appeared. Using

Einstein’s relativity equations, Karl

Schwarzchild predicted the existence of a

dense object into which other objects could

fall but out of which no objects could ever

come. Today, we call Schwarzchild’s object

a black hole.

A Magic Sphere?

Schwarzchild also predicted a magic

sphere around such an object where gravity

is so powerful that nothing can move

outward. This distance is referred to

today as the event horizon, because no

information about events occurring inside

this distance can ever reach us. Unable to

withstand the pull of gravity, all material

that goes past the event horizon is crushed

until it becomes a point of infinite density

occupying virtually no space. This point is

known as the singularity: Every black hole

has a singularity at its center.

They Come in All Sizes

There are three main types of black holes.

Stellar-mass black holes, the smallest and

most common, are the explosions of massive

stars. Medium-size black holes are probably

the result of mergers of smaller black holes,

and supermassive black holes have huge

masses and exist in the center of galaxies.

How Do We Know They Exist?

In 2002, R. Schodel and his research

team reported the first observation of the

orbit of a star around the black hole at the

center of our galaxy, the Milky Way. For

many years, astronomers have put forth

the theory that supermassive black holes—

more than a million times the mass of the

Sun—exist in nearly every galaxy. No one,

however, had found conclusive evidence

that supermassive black holes exist.

The Sun takes 230 million years to circle

the Milky Way, but the star that Schodel

reports on will complete its orbit around

the black hole in 15 years. The speed of the

star’s orbit indicates that it is getting closer

and closer to a huge gravitational pull. For

scientists, this orbit provides the evidence

that supermassive black holes exist.

Applying Critical-Thinking Skills

Directions: Answer each question or respond to each statement.

1. Describe what would be happening to you if you were falling into a massive black

hole. As you approach the event horizon, feet first, your body begins to be stretched

out. Why is that happening? What happens at the event horizon?

2. Predict what will happen when you travel past the event horizon.

Stars and Galaxies 59

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LESSON 3

The Lives of Stars

Stars exist because of gravity. The mutual gravitational attraction of particles in a thin,

gaseous cloud causes the cloud to collapse. As the cloud is squeezed to extremely high

pressures, its temperature rises, igniting its nuclear reactions, and a star is born.

Research and Diagram the Evolution of Stars

1. Research the evolutionary stages of three types of stars.

a. low-mass stars

b. medium-mass stars (about the size of the Sun)

c. massive stars

2. On chart paper, draw a diagram of the evolutionary stages of each type of star, beginning

each one with a nebula. Draw the stages in color and label each stage.

3. On each diagram, label the star in its main-sequence stage with its temperature range in

degrees Kelvin.

Research Notes:

60 Stars and Galaxies

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Make and Use Graphs LESSON 3: 45 minutes

How can graphing data help you understand stars?

How can you make sense of everything in the universe? Graphs help you organize information.

The Hertzsprung-Russell diagram is a graph that plots the color, or temperature, of stars against

their luminosities. What can you learn about stars by plotting them on a graph similar to the

H-R diagram?

Materials

colored adhesive stars of various sizes

Learn It

Displaying information on graphs makes it

easier to see how objects are related. Lines

on graphs show you patterns and enable you

to make predictions. Graphs display a lot of

information in an easily understandable

form. In this activity, you will make and

use graphs, plotting the temperature, the

color, and the mass of stars.

Try It

1. Using the graph paper, draw a graph

like the one shown in your book.

graph paper

2. Use the color and temperature data in

the table below to plot the position of

each star on your graph. Mark the points

by attaching adhesive stars to the graph.

3. If stars have similar data, plot them in

a cluster. Label each star with its name.

4. Draw a curve that joins the data points

as smoothly as possible.

5. Make another graph and plot

temperature v. mass of the stars in the

table. Use the grid on the next page.

|Star |Color |Temperature (K) |Mass in solar masses |

|Sun |Yellow |5,700 |1 |

|Alnilam |Blue-white |27,000 |40 |

|Altair |White |8,000 |1.9 |

|Alpha Centauri A |Yellow |6,000 |1.08 |

|Alpha Centauri B |Orange |4,370 |0.68 |

|Barnard’s Star |Red |3,100 |0.1 |

|Epsilon Eridani |Orange |4,830 |0.78 |

|Hadar |Blue-white |25,500 |10.5 |

|Proxima Centauri |Red |3,000 |0.12 |

|Regulus |White |11,000 |8 |

|Sirius A |White |9,500 |2.6 |

|Spica |Blue-white |22,000 |10.5 |

|Vega |White |9,900 |3 |

Stars and Galaxies 61

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Skill Practice continued

Apply It

6. All of the stars on your graph are main-sequence stars. What is the relationship

between the color and the temperature of a main-sequence star?

7. What is the relationship between the mass and the temperature of a main-sequence

star? How are color and mass related?

8. Key Concept Which star would be the most likely to eventually form a black

hole? Why?

62 Stars and Galaxies

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LESSON 3

Evolution of Stars

True or False

Directions: On the line before each statement, write T if the statement is true or F if the statement is false. If the

statement is false, change the underlined word(s) to make it true. Write your changes on the lines provided.

1. A cold, dense, dark cloud of gas and dust in space is called a nebula.

2. The gravity of a white dwarf is so great that light cannot escape it.

3. A supernova is the explosion of a massive star.

4. A dense core that remains after a supernova is called a black hole.

5. Stars move onto the main sequence when they begin to fuse hydrogen into carbon.

Multiple Choice

Directions: On the line before each question, write the letter of the correct answer.

6. Which sequence correctly shows how stars form?

A. nebula forms → nebula collapses → protostar forms → fusion begins

B. protostar forms → nebula forms → fusion begins → nebula collapses

C. nebula forms → protostar forms → nebula collapses → fusion begins

7. Which statement is true of stellar evolution?

A. Black holes become neutrons stars.

B. Low-mass stars become supergiants.

C. The most massive stars do not become white dwarfs.

8. How do stars recycle matter?

A. They stay on the main sequence.

B. Black holes form and recycle stellar gas for new stars.

C. Gravity pulls together gases and matter from old stars to create new ones.

Stars and Galaxies 63

Name Date Class

LESSON 3

Evolution of Stars

Completion

Directions: On each line, write the term from the word bank that correctly completes each sentence. Not all

terms are used

|black hole |main sequence star |nebula |neutron star |

|planetary |nebula protostar |red giant |red supergiant |

|supernovae |white dwarf | | |

1. A is a hot, dense, slowly cooling sphere of carbon that

forms at the end of the life cycle of stars such as the Sun.

2. A star is born deep inside a cloud of gas and dust called a .

3. Stars that are more than 10 times more massive than the Sun will explode

as .

4. A forms when the most massive stars collapse.

5. A small, extremely dense core of neutrons that remains after a supernova is called

a .

Short Answer

Directions: Respond to each statement on the lines provided.

6. Summarize the formation of a star.

7. Describe how a star’s mass affects the length of its life cycle.

8. Explain how star matter is recycled.

64 Stars and Galaxies

-----------------------

Launch Lab

Content Vocabulary

Lesson Outline

Mini Lab

Content Practice A

Content Practice B

School to Home

Key Concept Builder

Key Concept Builder

Key Concept Builder

High-Mass Stars

Low- Mass Stars

Key Concept Builder

Enrichment

Challenge

Skill Practice

Lesson Quiz A

Lesson Quiz B

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