# No Escape: The Truth About Black Holes

## Teacher Page: Lesson Plan

Index:

Goal / purpose
Desired learning outcomes
Prerequisites
New vocabulary
General misconceptions
Preparation time
Execution time
Physical layout of room
Materials
Procedure / directions
Evaluation / assessment
Activities / extensions
One computer classroom
Classrooms without computers
Home schooler

Goal / purpose:

The goal of this lesson is to provide factual information that will allow students to extend their understanding of basic physical concepts that apply to the study of black holes. Students will see how physics and mathematics are used to predict the existence and properties of these invisible objects. Students will learn how the Hubble Space Telescope is gathering data to further mankind's understanding of black holes. The module is designed as a research source for individual exploration of the black hole topic. Students can use the information available in this interactive lesson to research types of black holes, investigate the history of scientific ideas that led to today's concept of black holes, and to test their understanding of the nature of black holes. The assessment component is designed to provide students with an opportunity to practice communicating results of their Internet research to a specified audience.

Desired learning outcomes:

After completing No Escape: The Truth About Black Holes, students will be able to:

1. Distinguish between an event horizon and an accretion zone of a black hole.

2. Define escape velocity, black hole, and the speed of light.

3. Explain the relationship between escape velocity, black hole, and the speed of light.

4. Identify more than one single type of black hole.

5. State that the theory of black holes is built upon the work of many scientists over an extended time period.

Concepts:

· The escape velocity of a planet or star depends upon its mass and radius.
· Gravity is a basic force of nature created between objects that have mass.
· The speed of light, 300,000 km/s, is the universal "speed limit."
· The current theory of black holes is the result of contributions by many scientists over an extended time period.
· A black hole is the result of runaway gravity that compresses mass into a singularity.

Prerequisites:

Before completing the informational sections of the module, a student should be familiar with the concepts of:

· mass versus weight
· velocity
· gravity
· speed of light

New vocabulary:

· accretion disk
· Big Bang Theory
· black hole
· blueshift
· conservation of energy and mass
· density
· escape velocity
· event horizon
· G (gravitational constant)
· gravity
· kinetic energy
· magnetic field lines
· miniature black hole
· neutron star
· potential energy
· redshift
· resolution
· singularity
· speed of light
· stellar black hole
· supermassive black hole
· white dwarf

General misconceptions:

Many of these misconceptions are addressed in the activity section entitled: "What Do You Know about Black Holes?" in which the student chooses "myth" or "fact" in response to a series of questions.

Black holes exist only in theory.

Recent observations obtained by the Hubble Space Telescope have given considerable support to the presence of supermassive black holes at the centers of some galaxies, but there is not yet absolute proof. There has been very good evidence for the existence of stellar black holes for at least 20 years, based on the effects of an unseen companion in the double-star system, Cygnus X-1. The existence of black holes seems likely, given our understanding of physical processes, but it is not absolutely confirmed.

Black holes are giant cosmic vacuum cleaners that swallow up everything around them.

In reality, at a given distance from its center a black hole creates the same gravity as would a normal object with the same mass. Therefore, black holes at a distance do not attract matter more strongly than ordinary stars do. However, another important factor that determines the magnitude of the force of gravity is the radius of the object. The mass of a black hole is so compressed that it is possible to get very close to its center (see Science Background section), where gravity will be enormously strong.

Black holes can be detected visually.

We observe black holes indirectly by the effect they have on material around them, but by definition a black hole cannot be "seen."

Our Sun will become a black hole.

Only stars that are more massive than our Sun might become black holes when they run out of fuel at the end of their lives. The Sun is not massive enough to become a black hole. When the Sun dies, it will lose its outer layers gently and its core will contract to great density (about 1 ton per cubic centimeter), but the gravity of the small core will not be enough to overpower the pressure caused by atomic forces that separate electrons and atomic nuclei. This state of matter is called a white dwarf and it is the fate of our Sun.

Black holes and wormholes are connected.

People often associate wormholes with black holes. The existence of black holes has been inferred by their effect on nearby matter. Astronomers, however, have never observed wormholes. Theory suggests that wormholes are shortcuts through space and time linking two points. People may think wormholes are real because they saw them in science fiction movies and television shows. Wormholes also are associated with white holes, another cosmic object that exists in mathematical theory, but hasn't been observed in nature. White holes, as the theory goes, are regions of space into which nothing can fall.

Preparation time:

You will need time to download computer software to support the lesson (Netscape Navigator 3.0 or 4.0, or Explorer) if it is not already installed.

Teachers should allow time to preview the Science Background information. We suggest that they become familiar with each of the modules.

Execution time by module:

The amount of time needed to complete any of these modules will vary depending on such factors as the length of available teaching time and the number of students per computer. One way to jump start your lesson is to do a module (or part of one) together with the students. This can be done as a directed activity using an overhead projector, a LCD, or a TV monitor to project the lesson to the entire class. The following are estimated times:

Is a Black Hole Really a Hole? — 25 - 30 minutes

Beats Us - You Explain It — 30 minutes

Physical layout of room:

Students can work in small groups of two or three, or individually. Adaptations can be made to accommodate classrooms with only a single Internet computer. This might include using an overhead projector with a LCD that projects the computer image on a screen or a hookup from a computer to a television monitor.

You can also do the lesson off the Internet! Different software programs, available through commercial vendors, provide off-line access to the Internet. These programs allow you to save Web pages to your local hard drive. Using your browser you can then open the lesson on your computer. The advantage is that the speed of an Internet connection will not slow down the use of the lesson. However, any links in the teacher pages to outside Web pages will not function.

Materials:

This lesson requires a computer with a color monitor and Internet connection. The Web browser used must have at least the capability of running Netscape Navigator 3.0 or better/Microsoft Internet Explorer 4.0 or better. For additional information read the Computer Needs section.

Procedure / directions:

These are self-directed activities. Students can work independently or in small groups to complete each lesson module.

Any module can be accessed at any time. This lesson does not require the student to start at the beginning, although students may discover that it is wise to start with the information section of the module.

Activities / extensions:

Engagement Activity

Here are some suggestions to pre-assess your students' understanding of escape velocity, gravity, and black holes:

1. Myth or Fact? - Ask students to test their prior knowledge about black holes by doing the Myth or Fact section in the module What is a Black Hole?

2. Ask students to relate either a movie or a story that uses a black hole as a theme. A few examples follow:

Yolen, Jane. Commander Toad and the Big Black Hole. Coward-McCann, Inc., New York, 1983.

Walt Disney Productions. The Black Hole Storybook. Adapted by Shep Stenemanl. Random House, New York, 1979.

Benford, Gregory. Sailing Bright Eternity. Bantam Doubleday Dell Publishing, New York, 1995.

Crichton, Michael. Sphere. Knopf, New York, 1987.

3. Have the students distinguish between the concept of "orbital velocity" and "escape velocity." Have the students discuss whether these values would change if they were on another planet.

Pre-assessment activity

Ask students to explain in 200 words or fewer what a black hole is and share their essays with the class. Students go through a similar exercise in the module Beats Us — You Explain It. This activity will show students what they have learned after the lesson is completed. Ask them to compare their initial ideas about black holes with what they know now.

Online activity: Step-by-step instructions

Is a Black Hole Really a Hole? This is an introduction module to the concept of a black hole. Students examine the anatomy of a black hole using a diagram of an accretion disk, the event horizon, and jets of hot gas. This module also includes subsections about myths, the history related to the discovery of black holes, an animated trip to the center of a black hole and a discussion of different types of black holes.

In Beats Us — You Explain It, students are asked to explain the concept of a black hole to a targeted audience in 200 words or fewer. Images are provided for students to use as illustrations for their descriptions. With a "submit" button, these essays can be submitted to the Space Telescope Science Institute. The Office of Public Outreach at the Institute will select some of the best essays and post them on this Web site.

Extension Activity

1. Black holes history: Ask students to read the subsection about the history of the discovery of black holes (found in the module "What is a Black Hole?") and do further research on the scientists mentioned. This information could be presented by the students as an essay or a poster.

2. Have the students complete the Time Line Activity, putting some technological advancements into time context with dates of the black hole history [see below].

3. Perform a Density Lab Activity [see below].

4. Have students calculate the number of teachers that would have sufficient mass to form a black hole if they were stuffed into a VW bug [see below].

Black Hole Accessory Time Line Activity

Create a time line to accompany the existing text. This time line would span the period discussed in the history but would highlight different events. The line would cover:

1600 1650 1700 1750 1800 1850 1900 1950 2000 A.D.

Include these (or similar) items:

1600 - First performance of Shakespeare's Hamlet
1670 - Pilgrims land at Plymouth Rock
1750 - Calendar reform in Britain makes 1 January the official first day of the year
1778 - James Cook visits Hawaii and reports its existence to Europe
1792 - Beginning of Napoleonic Wars
1846 - Potato Blight in Ireland results in massive immigration to other countries
1865 - U.S. Civil War
1901 - First electric typewriter
1940 - First antibiotics
1957 - First artificial Earth satellite
1965 - First communication satellite
1977 - Apple II personal computer launched
1981 - Introduction of IBM PC
1982 - CD players made available

Density Activities

Background information

Density is a physical property of a substance. At any given temperature and pressure the density of a material is constant. Density is related to two attributes: mass and volume. This gives rise to the formula: Density = Mass per Volume [D = M / V].

In a laboratory it is possible to determine the mass of an object using a balance. It is also easy to determine the volume of a material; for example, a graduated cylinder can be used to find the volume of a liquid. The volume of a regularly shaped solid can be determined mathematically. It gets a little trickier to determine the volume of an irregular solid; you have to use displacement of water (Archimedes Principle) to find the volume. Although black holes tend to involve density of gaseous materials, it is much easier for students to grasp the concept of density using items they can easily see such as solids and liquids.

Density is typically expressed in grams / cubic centimeter (g/cm3). Equal volumes of different liquids do not necessarily have the same mass. You can demonstrate this by setting up the following situation. All you need are equal volumes of water and corn oil (less dense than water) or corn syrup (more dense than water).

The mass of water is greater than the mass of the corn oil since the water-side is tipped lower than the oil-side of the scale. At 4°C, the mass of 1 cm3 of water is 1 gm; so the density of water at this temperature is 1 gm/cm3. The density of the oil is less than that of water since an equal volume has less mass.This is the reason that oil floats on water. If corn syrup is used, the scales will tip toward the corn-syrup side, showing that the corn syrup has more mass than an equal volume of water. The corn syrup is denser than water. Since corn syrup will dissolve in water, care must be exercised when showing how water will float on the corn syrup. Start by placing the corn syrup in a container such as a graduated cylinder. Then tip the cylinder on its side and slowly pour the water down the side to avoid mixing the two liquids.

The volume of a sphere, such as a marble, can be determined mathematically by use of the formula:

The volume of a cube can be determined by the formula:

V = l × w × h

The volume of an irregular solid, such as a stone, can be determined by displacement of water. Fill an overflow can so that the water is just above the level of the spout and plug the spout with your finger. Place the overflow can on the counter with its spout above a sink or put the can in a catch basin, uncover the spout and allow the excess water to flow out. Now position a graduated cylinder under the over-flow spout to catch the water that will flow out. Carefully drop the irregularly shaped object into the can and catch the overflowing water in the cylinder. Read the volume of water collected in the graduated cylinder using the markings on the side. The volume of water in the cylinder is equal to the volume of the object.

Activity: Have students determine the density of a variety of materials using a balance for mass determination and the appropriate method for volume determination.

Creating a Black Hole on Earth — Using Teachers

Introduction:

In theory, if you could compress enough teachers (mass) into a small volume (a VW bug), their combined gravitational pull would be sufficient that the escape velocity would exceed that required by the speed of light. In essence a black hole would be created. How many teachers with an average mass of 70 kg each would be required?

Assumptions:

Teachers typically walk at 6 km/hr — assume this as velocity. The average mass of a typical teacher is 70 kg. Assume that the Volkswagen is spherical in shape (a stretch, but a useful assumption) with a diameter of 3 m. The mass of the car is 230 kg.

Hints:

Convert walking speed to m/s.

Find the mass of an object with a radius of 1.5 m whose escape velocity is equal to the walking speed in m/s.

Divide the total mass by 70 kg to determine the number of teachers required to equal total mass. You can ignore the mass of the car because it is negligible when compared with the teacher's mass.

Constant values:

Speed of light = "c" = 2.99793 × 108 m/s

Rounded to = 3.0 × 108 m/s

Gravitational constant = "G" = 6.67 × 10-11 m3/kg .sec2

Mass = "M" = [in kg]

Calculation:

1. Vescape2 = c2 = 2GM / r

2. M = rc2 / 2G

3.

 Mtot = 1.5 m ( 3 × 108 m/s)2 ——————————————— 2 ( 6.67 × 10 -11 m3 / kg . sec2)

4. Mtot = 1.01 × 1027 kg

5.

 Nteachers = Mtot —————— Mone teacher

6.

 Nteachers = 1.01 × 1027 kg ———————— 70 kg / teacher

7. Nteachers = 1.44 × 1025 = 14,400,000,000,000,000,000,000,000

Evaluation / assessment:

Assessment strategies built into the lesson:

1. In How Much Do You Know About Black Holes?, students get to self-assess their knowledge of myths and facts associated with black holes.

2. In the module, Beats Us — You Explain It, students are asked to write a description of black holes tailored to a specific audience using 200 words or fewer. After completing this lesson you might have students compare their final description with what they wrote before the lesson.

Follow-up Activities / Interdisciplinary connections:

You can find information about black holes at the Space Telescope Science Institute. Hardcopy versions of images observed by the Hubble Space Telescope and other NASA missions related to black holes are also available at your closest NASA Educator Resource Center: http://teacherlink.ed.usu.edu/tlnasa/

Connections to other disciplines can be used to broaden classroom discussion of the general principles learned in No Escape: The Truth About Black Holes.

English:

1. The lives and careers of the scientists involved in the development of the theory of black holes make interesting topics for research projects. Some of these scientists are listed in a subsection in the first module of the lesson.

2. Many writers have been inspired by the concept of black holes and have produced very interesting essays and stories. These writings can be evaluated by the students for scientific accuracy or other perspectives.

3. Describe how science fiction movies and TV shows have depicted black holes.

One-computer classroom:

It is recommended that teachers project the images from the computer onto a classroom screen using an overhead LCD or television screen. Here are two suggestions to facilitate a large group presentation and to avoid last-minute glitches that can happen when using the Internet.

1. Bookmark a selected part of the lesson, such as one of the modules that you wish to use, and download it onto your hard disk. This will eliminate the inconvenience of possible Internet service interruptions.

2. Another way to prepare is to print selected parts of the lesson as paper copies.

Students may work on the lesson independently or in small groups. Alternatively, teachers might want to complete the activity with the entire class.

Hardcopy versions of data taken by the Hubble Space Telescope and other NASA missions related to black holes are also available at your closest NASA Educator Resource Center: http://teacherlink.ed.usu.edu/tlnasa/

Classrooms without computers:

Here are some suggestions:

1. If you have access to a computer with World Wide Web capabilities at home or in the school library, you may print selected parts of the lesson as paper copies or transparencies.

2. If your school has one or more computers located outside your classroom, (i.e. library, computer lab) students can experience the lesson individually or in small groups as a learning station or as a supplement to your gravity or mathematics unit.

3. Some students might have computers at home with access to the Internet. In this case, you might consider assigning sections of the lesson for homework or extra credit.

4. NASA has available FREE, at your closest NASA Educator Resource Center: http://teacherlink.ed.usu.edu/tlnasa/,
lithographs and posters related to black holes which can be used as teaching tools in the classroom.

Home schooler:

This lesson is easily followed without additional teacher support if the prerequisites are met. Parents can preview the lesson and examine the teacher pages ahead of time. A wealth of information can be found at Hubblesite, the Hubble Space Telescope's web site at the Space Telescope Science Institute. Here you can find background information on the telescope, pictures and news releases of past and present stories, education activities, and other science resources.