lesson 3 | evolution of starsimages.pcmac.org/.../chapter_22_notes_l_3.pdf · lesson outline lesson...

46 Stars and Galaxies

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Student Labs and Activities Page

Launch Lab 47

Content Vocabulary 48

Lesson Outline 49

MiniLab 51

Content Practice A 52

Content Practice B 53

School to Home 54

Key Concept Builders 55

Enrichment 59

Challenge 60

Skill Practice 61

Lesson 3 | Evolution of Stars

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Stars and Galaxies 47

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Do stars have life cycles?You might have learned about the life cycles of plants or animals. Do stars, such as the Sun, have life cycles? Before you find out, review the life cycle of a sunflower.

Procedure

Launch Lab

1. Read and complete a lab safety form.

2. Obtain an envelope containing slips of paper that explain the life cycle of a sunflower.

3. Use colored pencils to draw a sunflower in the middle of a piece of paper, or use a glue stick to glue a sunflower picture on the paper.

4. Using your knowledge of plant life cycles, arrange the slips of paper around the sunflower in the order in which the events listed on them occur. Draw arrows to show how the steps form a cycle.

Think About This 1. Does the life cycle of a sunflower have a beginning and an end? Explain your answer.

2. Do you think that every stage in the life cycle takes the same amount of time? Why or why not?

3. Key Concept How do you think the life cycle of a star compares to the life cycle of a sunflower? Do you think all stars have the same life cycle?

LESSON 3: 20 minutes

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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.

Content Vocabulary LESSON 3



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Lesson Outline 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 .



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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.

Lesson Outline continued



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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

LESSON 3: 15 minutesMiniLab

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 cardboardon 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?



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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.

Content Practice A LESSON 3



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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?

Content Practice B LESSON 3



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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.

School to Home LESSON 3

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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 true. 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.

Key Concept Builder LESSON 3

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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).



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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


High-Mass Stars

Low-Mass Stars



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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.




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Into the Darkness

Enrichment

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 SizesThere 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 SkillsDirections: 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.

LESSON 3

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Challenge

The Lives of StarsStars 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:

LESSON 3

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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?

Materialscolored adhesive stars of various sizes graph paper

Make and Use GraphsSkill Practice LESSON 3: 45 minutes

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.

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

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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?

Skill Practice continued

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lesson 3 | evolution of starsimages.pcmac.org/.../chapter_22_notes_l_3.pdf · lesson outline lesson...

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