Question
For the first 150 million years after the Big Bang,1 there were no galaxies or stars or planets. The universe was featureless.
As time passed, the first stars formed. Stars collected into galaxies. Galaxies began to cluster together. Those clusters are made up of the galaxies and all the material between the galaxies. Clumps of matter smashed into each other, and the planets in our solar system began to form around the sun. Something must hold our solar system, galaxies, and clusters of galaxies together. And gravity is that “glue.”
In some clusters, the space between galaxies is filled with gas so hot, scientists cannot see it using visible light telescopes. The gas only can be seen as X-rays or gamma rays.2 Scientists look at that gas and measure how much there is between galaxies in clusters. By doing this, they discovered that there must be five times more material in the clusters than we can detect. The invisible matter that we can’t detect is called “dark matter.”
The Swiss astronomer Fritz Zwicky first used the term “dark matter” in the 1930s. He studied the so-called Coma galaxy cluster and, specifically, how fast it revolves. Clusters are like merry-go-rounds: their speed of revolution depends on the weight and position of the objects in the clusters, like the weight of the objects and their positions on a merry-go-round. The speed he measured hinted that the cluster had much more mass than the observable light suggested.
In the 1970s, U.S. astronomer Vera Rubin and her colleagues confirmed this result by studying galaxy rotation. They also discovered single galaxies, not just clusters, have more mass than their observable light suggested. The work of Rubin and her team helped to firmly establish the notion of dark matter.
In many ways, scientists know more about what dark matter is not, though they do have a few ideas about what it could be.
Dark matter possibly could be brown dwarfs, “failed” stars that never ignited because they lacked the mass needed to start burning. Dark matter could be white dwarfs, the leftover parts of cores of dead small- to medium-size stars. Or dark matter could be neutron stars or black holes, the leftover parts of large stars after they explode.
However, problems exist with each of these suggestions. Scientists have strong evidence there aren’t enough brown dwarfs or white dwarfs to account for all the dark matter. Black holes and neutron stars, too, are rare.
Dark matter may not be made up of the matter we are familiar with at all. The matter that makes up dark matter could be different. It may be filled with particles predicted by theory but that scientists have yet to observe.
Because scientists can’t see dark matter directly, they have found other ways to investigate it. We can use indirect ways to study things, like looking at a shadow and making an educated guess about what’s casting the shadow. One way scientists indirectly study dark matter is by using gravitational lensing.
Light going through a gravitational lens is similar to light going through an optical lens:3 it gets bent. When light from distant stars passes through a galaxy or cluster, the gravity of the matter present in the galaxy or cluster causes the light to bend. As a result, the light looks like it is coming from somewhere else rather than from its actual origin. The amount of bending helps scientists learn about the dark matter present. Many NASA scientists use the Hubble Space Telescope to observe gravitational lensing.
In addition to these indirect ways, scientists at NASA think they have a direct way to detect dark matter using the Fermi Gamma-Ray Space Telescope. This telescope looks at gamma rays, the highest energy form of light. When two dark matter particles crash into each other, they might release a gamma ray. The Fermi Telescope could theoretically detect these collisions, which would appear as a burst of a gamma ray in the sky. Because Fermi has not been in space very long, scientists do not yet have enough data to form conclusions.
That’s what makes dark matter exciting: it’s still one of the great mysteries of science.
Question 24
What is the central idea of the text?
A. Dark matter is a potential source of energy for Earth.
B. Dark matter is invisible matter that scientists study indirectly.
C. Dark matter is created from the remains of dead or failed stars.
D. Dark matter is becoming increasingly difficult for scientists to locate.
Question 25
Why does the author compare galaxy clusters to "merry-go-rounds" in paragraph 4?
A. to show how quickly galaxies rotate in space
B. to show that galaxy clusters never stop revolving
C. to show how weight and position affect revolution speed
D. to show how common rotating galaxy clusters are in space
Question 26
What connection does the author draw between the revolution speed of galaxy clusters and dark matter? (Paragraph 4)
A. The revolution speed can result in new dark matter.
B. The revolution speed can result in a loss of dark matter.
C. The revolution speed makes it difficult to see dark matter.
D. The revolution speed may indicate whether dark matter is present.
Question 27
Which statement best describes the theories about dark matter mentioned in paragraphs 7-8?
A. They have been tested in a laboratory.
B. These are the only theories about dark matter.
C. There is evidence that contradicts these theories.
D. The evidence supporting these theories is very strong.
Question 28
How does paragraph 9 contribute to the reader's understanding of dark matter?
A. It highlights how mysterious dark matter is.
B. It lists the elements known to be in dark matter.
C. It prompts readers to guess what dark matter is made of.
D. It suggests that scientists will never know what dark matter is.
Question 29
What is one way in which scientists study dark matter?
A. They study how light bends around a galaxy or galaxy cluster.
B. They study shadows that are cast onto a galaxy or galaxy cluster.
C. They study changes in the number of galaxies in a galaxy cluster.
D. They study how the brightness within a galaxy or galaxy cluster changes.
Question 30
What is the meaning of "theoretically" in paragraph 12?
A. certainly
B. improbably
C. supposedly
D. unknowingly
Question 31
How might the Fermi Telescope help scientists study dark matter? (Paragraph 12)
A. by making dark matter visible
B. by recording rotation speed
C. by observing bending light
D. by detecting gamma rays
Question 32
Which quote from the text best summarizes scientists' knowledge about dark matter?
A. "Vera Rubin and her colleagues confirmed this result by studying galaxy rotation." (Paragraph 5)
B. "In many ways, scientists know more about what dark matter is not, though they do have a few ideas about what it could be." (Paragraph 6)
C. "Because scientists can't see dark matter directly, they have found other ways to investigate it." (Paragraph 10)
D. "When two dark matter particles crash into each other, they might release a gamma ray." (Paragraph 12)
Question 33
What is the author's overall purpose in the text?
A. to explain the mysteries of dark matter
B. to explain what dark matter is made of
C. to propose a new theory about dark matter
D. to encourage more research into dark matter
As time passed, the first stars formed. Stars collected into galaxies. Galaxies began to cluster together. Those clusters are made up of the galaxies and all the material between the galaxies. Clumps of matter smashed into each other, and the planets in our solar system began to form around the sun. Something must hold our solar system, galaxies, and clusters of galaxies together. And gravity is that “glue.”
In some clusters, the space between galaxies is filled with gas so hot, scientists cannot see it using visible light telescopes. The gas only can be seen as X-rays or gamma rays.2 Scientists look at that gas and measure how much there is between galaxies in clusters. By doing this, they discovered that there must be five times more material in the clusters than we can detect. The invisible matter that we can’t detect is called “dark matter.”
The Swiss astronomer Fritz Zwicky first used the term “dark matter” in the 1930s. He studied the so-called Coma galaxy cluster and, specifically, how fast it revolves. Clusters are like merry-go-rounds: their speed of revolution depends on the weight and position of the objects in the clusters, like the weight of the objects and their positions on a merry-go-round. The speed he measured hinted that the cluster had much more mass than the observable light suggested.
In the 1970s, U.S. astronomer Vera Rubin and her colleagues confirmed this result by studying galaxy rotation. They also discovered single galaxies, not just clusters, have more mass than their observable light suggested. The work of Rubin and her team helped to firmly establish the notion of dark matter.
In many ways, scientists know more about what dark matter is not, though they do have a few ideas about what it could be.
Dark matter possibly could be brown dwarfs, “failed” stars that never ignited because they lacked the mass needed to start burning. Dark matter could be white dwarfs, the leftover parts of cores of dead small- to medium-size stars. Or dark matter could be neutron stars or black holes, the leftover parts of large stars after they explode.
However, problems exist with each of these suggestions. Scientists have strong evidence there aren’t enough brown dwarfs or white dwarfs to account for all the dark matter. Black holes and neutron stars, too, are rare.
Dark matter may not be made up of the matter we are familiar with at all. The matter that makes up dark matter could be different. It may be filled with particles predicted by theory but that scientists have yet to observe.
Because scientists can’t see dark matter directly, they have found other ways to investigate it. We can use indirect ways to study things, like looking at a shadow and making an educated guess about what’s casting the shadow. One way scientists indirectly study dark matter is by using gravitational lensing.
Light going through a gravitational lens is similar to light going through an optical lens:3 it gets bent. When light from distant stars passes through a galaxy or cluster, the gravity of the matter present in the galaxy or cluster causes the light to bend. As a result, the light looks like it is coming from somewhere else rather than from its actual origin. The amount of bending helps scientists learn about the dark matter present. Many NASA scientists use the Hubble Space Telescope to observe gravitational lensing.
In addition to these indirect ways, scientists at NASA think they have a direct way to detect dark matter using the Fermi Gamma-Ray Space Telescope. This telescope looks at gamma rays, the highest energy form of light. When two dark matter particles crash into each other, they might release a gamma ray. The Fermi Telescope could theoretically detect these collisions, which would appear as a burst of a gamma ray in the sky. Because Fermi has not been in space very long, scientists do not yet have enough data to form conclusions.
That’s what makes dark matter exciting: it’s still one of the great mysteries of science.
Question 24
What is the central idea of the text?
A. Dark matter is a potential source of energy for Earth.
B. Dark matter is invisible matter that scientists study indirectly.
C. Dark matter is created from the remains of dead or failed stars.
D. Dark matter is becoming increasingly difficult for scientists to locate.
Question 25
Why does the author compare galaxy clusters to "merry-go-rounds" in paragraph 4?
A. to show how quickly galaxies rotate in space
B. to show that galaxy clusters never stop revolving
C. to show how weight and position affect revolution speed
D. to show how common rotating galaxy clusters are in space
Question 26
What connection does the author draw between the revolution speed of galaxy clusters and dark matter? (Paragraph 4)
A. The revolution speed can result in new dark matter.
B. The revolution speed can result in a loss of dark matter.
C. The revolution speed makes it difficult to see dark matter.
D. The revolution speed may indicate whether dark matter is present.
Question 27
Which statement best describes the theories about dark matter mentioned in paragraphs 7-8?
A. They have been tested in a laboratory.
B. These are the only theories about dark matter.
C. There is evidence that contradicts these theories.
D. The evidence supporting these theories is very strong.
Question 28
How does paragraph 9 contribute to the reader's understanding of dark matter?
A. It highlights how mysterious dark matter is.
B. It lists the elements known to be in dark matter.
C. It prompts readers to guess what dark matter is made of.
D. It suggests that scientists will never know what dark matter is.
Question 29
What is one way in which scientists study dark matter?
A. They study how light bends around a galaxy or galaxy cluster.
B. They study shadows that are cast onto a galaxy or galaxy cluster.
C. They study changes in the number of galaxies in a galaxy cluster.
D. They study how the brightness within a galaxy or galaxy cluster changes.
Question 30
What is the meaning of "theoretically" in paragraph 12?
A. certainly
B. improbably
C. supposedly
D. unknowingly
Question 31
How might the Fermi Telescope help scientists study dark matter? (Paragraph 12)
A. by making dark matter visible
B. by recording rotation speed
C. by observing bending light
D. by detecting gamma rays
Question 32
Which quote from the text best summarizes scientists' knowledge about dark matter?
A. "Vera Rubin and her colleagues confirmed this result by studying galaxy rotation." (Paragraph 5)
B. "In many ways, scientists know more about what dark matter is not, though they do have a few ideas about what it could be." (Paragraph 6)
C. "Because scientists can't see dark matter directly, they have found other ways to investigate it." (Paragraph 10)
D. "When two dark matter particles crash into each other, they might release a gamma ray." (Paragraph 12)
Question 33
What is the author's overall purpose in the text?
A. to explain the mysteries of dark matter
B. to explain what dark matter is made of
C. to propose a new theory about dark matter
D. to encourage more research into dark matter
Answers
GPT-4o mini
Here are the answers to the questions based on the text:
**Question 24: What is the central idea of the text?**
**B. Dark matter is invisible matter that scientists study indirectly.**
**Question 25: Why does the author compare galaxy clusters to "merry-go-rounds"?**
**C. to show how weight and position affect revolution speed**
**Question 26: What connection does the author draw between the revolution speed of galaxy clusters and dark matter?**
**D. The revolution speed may indicate whether dark matter is present.**
**Question 27: Which statement best describes the theories about dark matter mentioned in paragraphs 7-8?**
**C. There is evidence that contradicts these theories.**
**Question 28: How does paragraph 9 contribute to the reader's understanding of dark matter?**
**A. It highlights how mysterious dark matter is.**
**Question 29: What is one way in which scientists study dark matter?**
**A. They study how light bends around a galaxy or galaxy cluster.**
**Question 30: What is the meaning of "theoretically" in paragraph 12?**
**C. supposedly**
**Question 31: How might the Fermi Telescope help scientists study dark matter?**
**D. by detecting gamma rays**
**Question 32: Which quote from the text best summarizes scientists' knowledge about dark matter?**
**B. "In many ways, scientists know more about what dark matter is not, though they do have a few ideas about what it could be."**
**Question 33: What is the author's overall purpose in the text?**
**A. to explain the mysteries of dark matter**
**Question 24: What is the central idea of the text?**
**B. Dark matter is invisible matter that scientists study indirectly.**
**Question 25: Why does the author compare galaxy clusters to "merry-go-rounds"?**
**C. to show how weight and position affect revolution speed**
**Question 26: What connection does the author draw between the revolution speed of galaxy clusters and dark matter?**
**D. The revolution speed may indicate whether dark matter is present.**
**Question 27: Which statement best describes the theories about dark matter mentioned in paragraphs 7-8?**
**C. There is evidence that contradicts these theories.**
**Question 28: How does paragraph 9 contribute to the reader's understanding of dark matter?**
**A. It highlights how mysterious dark matter is.**
**Question 29: What is one way in which scientists study dark matter?**
**A. They study how light bends around a galaxy or galaxy cluster.**
**Question 30: What is the meaning of "theoretically" in paragraph 12?**
**C. supposedly**
**Question 31: How might the Fermi Telescope help scientists study dark matter?**
**D. by detecting gamma rays**
**Question 32: Which quote from the text best summarizes scientists' knowledge about dark matter?**
**B. "In many ways, scientists know more about what dark matter is not, though they do have a few ideas about what it could be."**
**Question 33: What is the author's overall purpose in the text?**
**A. to explain the mysteries of dark matter**