Astronomy Test #3

This H-R diagram shows the life track of a 1 M Sun star from the time it first becomes a main-sequence star. Which numbered point represents the star when it has both hydrogen-fusing and helium-fusing shells around an inert carbon core?

Point 4

Sun = size of grapefruit. Approximately how large in diameter would the star Procyon B be on this same scale?

1 millimeter (the size of a grape seed)

For the white dwarf supernova, the luminosity 175 days after it reaches peak brightness is about __________ of the luminosity at peak brightness.

1%

When the Sun becomes a white dwarf with a surface temperature similar to its current surface temperature, what will its luminosity be?

10^-4 Lsun

Just before the Sun produces a planetary nebula, what will its approximate luminosity be?

10^4 Lsun

What is the approximate lifetime of a star whose mass is twice that of the Sun?

10^9 years

These diagrams represent four possible models for the universe. Which model presumes the existence of some type of dark energy in the universe?

Accelerating universe

What is the approximate luminosity of a star whose mass is twice that of the Sun?

10 Lsun

The figure below shows the future life stages of the Sun on an H-R diagram. Use this figure to answer the following questions. What will the Sun's approximate luminosity be during the subgiant stage?

10 Lsun See image #3

The H-R diagram is shown in the figure below. Answer the following questions based on the information given in the figure. What is the approximate luminosity of a star whose mass is 10 times that of the Sun?

10,000 Lsun See image #2

What is the approximate luminosity of a star whose mass is 3 times that of the Sun?

100 Lsun

Approximately how many days does it take for a massive star supernova to decline to 10% of its peak brightness?

100 days

This diagram represents an edge-on view of our Milky Way galaxy. Of the four labeled stars, which one is located closest to a place where evidence suggests we would find a 4-million-solar-mass black hole?

2

At peak brightness, the white dwarf supernova is approximately __________ times as luminous as the massive star supernova at its peak brightness.

3 See image #4

Sun = size of grapefruit. Approximately how large in diameter would the star Betelgeuse be on this same scale?

3 kilometers (the size of a small town)

Approximately how many days does it take for a white dwarf supernova to decline to 10% of its peak brightness?

30 days

Approximately how many days does it take for a massive star supernova to decline to 1% of its peak brightness?

300 days

When the Sun is a red giant, what will its approximate surface temperature be?

3500 K

The figure below uses zoom-ins to compare the sizes of giant and supergiant stars to the sizes of Earth and the Sun. Suppose we wanted to represent all of these objects on the 1-to-10-billion scale from Chapter 1, on which the Sun is about the size of a grapefruit. Approximately how large in diameter would the star Aldebaran be on this scale?

6 meters (roughly the size of a dorm room) See image #1

Study this H-R diagram. What is the spectral type of the star Sirius? (The red arrow helps you locate Sirius on the diagram.)

A

What is this a picture of?

A cluster of galaxies

This graph shows data collected by a gamma ray telescope. What kind of event is it showing?

A gamma ray burst from a distant galaxy See image #10

This photo shows an object located in the halo of our Milky Way galaxy. What kind of object is it?

A globular cluster of stars

This figure shows a "slice of the universe" from the Sloan Digital Sky Survey. What is the Sloan Great Wall (indicated by the arrow)?

A huge collection of galaxies extending a billion light-years in length See image #22

What does this diagram represent?

A particle and antiparticle colliding and converting all their mass into photons. See image #18

This Hubble Space Telescope photo shows a planetary nebula. What is the white dot in the center (indicated by the arrow)?

A white dwarf

Based on the curves shown here, which of the following statements best describes how we can distinguish a massive star supernova from a white dwarf supernova?

A white dwarf supernova is brighter at its peak and over a few months fades more steadily than a massive star supernova. See image #4

This figure shows an all-sky map of the cosmic microwave background recorded by the Planck telescope. How long did this light travel through space before it reached the telescope?

About 14 billion years

The bright object in this photo is a quasar in the center of a distant galaxy. According to current understanding, about how big is the source of the bright light?

About the size of our solar system

If you looked at the field of view seen in this Hubble Space telescope with your naked eye, about how big would it appear in the sky?

About the size of this period — . — viewed at arm's held at arm's length against the sky

Based on a comparison of the radio, infrared, and visible-light images, we can conclude that gas clouds containing molecules __________.

Absorb infrared starlight less effectively than they absorb visible starlight.

These diagrams represent four possible models for the universe. Each model shows how the size of the observable universe changes with time. Of the four models, which one gives the universe the oldest age at present?

Accelerating universe

This photo shows the famous Crab Nebula. What is it?

An expanding cloud of remains from a star that died in a supernova.

Study this H-R diagram. Which of the following stars is the largest in size (radius)? (The red arrows help you locate these stars on the diagram.)

Antares (Radius increases diagonally from lower left to upper right, and Antares is the farthest toward the upper right.)

Sirius, the brightest star in the night sky, is actually a binary star system: Sirius A is main-sequence star and Sirius B is a white dwarf. Nearly all the visible light we see from Sirius comes from Sirius A. But when we photograph the system with X-ray light, as shown here, Sirius B is the brighter of the two stars. Why?

As a white dwarf, Sirius B is much hotter than Sirius A and thus emits more X-rays. See image #5

Study this H-R diagram. Which of the following stars has (or had) the longest hydrogen burning lifetime? (The red arrows help you locate these stars on the diagram.)

Barnard's star (It is the lowest mass star and hence has the longest lifetime.)

Study this H-R diagram. Which of the following stars is the most massive? (The red arrows help you locate these stars on the diagram.)

Beta Centauri (Beta Centauri is highest up along the main sequence, which means it is the most massive.)

The image of radio emission uses different colors of light to represent different levels of brightness. Which color represents the lowest level of brightness?

Black/dark blue

This graph shows how the apparent brightness of an eclipsing binary system changes with time. Which of the four labeled regions represents the system at a time when one star is eclipsing the other?

Both II and IV

How do regions showing strong radio emission from molecules look in the infrared-light image? Are they bright or are they dark?

Bright

Which distance measurement technique is most suited to measuring objects at a distance of 10 million light-years?

Cepheids See image #15

What are the dark blobs (indicated by the red arrows) in this photograph from the Hubble Space Telescope?

Cold, dense molecular clouds in which stars are forming.

How do regions showing strong radio emission from molecules look in the visible-light image? Are they bright or are they dark?

Dark

Which standard-candle technique is best for measuring the distances of very distant galaxies?

Distant Standards

Which of the following diagrams best represents the scale of Earth in comparison to a neutron star?

Earth the biggest, neutron star the smallest

In this diagram, red balls represent protons and gray balls represent neutrons. What reaction is being shown?

Fusion of helium into carbon (Three helium nuclei fuse to make one carbon nucleus, releasing energy in the process.)

This photo shows the Large Magellanic Cloud, or LMC for short. Based on what you have learned in about the LMC from your text, which of the following statements about the LMC is not true?

Galaxies similar to the LMC are extremely rare.

Notice the blue ovals (such as those indicated by the arrows) in this image of a galaxy cluster. The oval structures are not really located where they appear to be, but instead are multiple images of a single galaxy that lies directly behind the cluster. What do we call the process that creates these multiple images?

Gravitational lensing

The data points in this diagram represent the measured speeds and distances of various galaxies, and the solid line represents a best fit to these data. The trend indicated by the solid line is known as _________.

Hubble's law

According to this diagram, how much more abundant is hydrogen in the universe than nitrogen?

Hydrogen is about 10,000 times as abundant as nitrogen.

A binary system that looks like the one shown in this painting should shine brightly in X-rays. Which one of the four labeled regions is the source of most of the X-rays?

II See image #9

Is this a photo of a spiral galaxy or an elliptical galaxy, and how do you know?

It is a spiral galaxy, because we can see a dusty disk going across the center.

The top panorama shows our view of the Milky Way in all directions as it appears in visible light. The bottom panorama shows the same view but in a different wavelength of light. What wavelength band are we seeing in the bottom photo, and how do you know?

Infrared light, because the dust that appears dark in the visible light photo glows in infrared light. See image #12

This star map shows stars as we see them in our sky from Earth, centered around the constellation Canis Major. Larger dots represent brighter stars, and a few of the brightest stars are identified. From this view alone, what can you conclude about Sirius?

It has the greatest apparent brightness of any star in this region of the sky.

This photo shows gas associated with a protostar. What is this gas doing?

It is flowing outward in two opposite directions from the protostar.

This diagram represents what we call a saddle-shaped geometry. In the context of this chapter, what is its significance?

It represents a two-dimensional analogy to one possible geometry for our universe. See image #20

What does this graph show?

It shows calculations indicating that the temperature of the universe began quite high but is now quite low. See image #17

The data points on this graph represent the measured spectrum of the cosmic microwave background, while the solid curve represents a theoretically calculated thermal radiation spectrum for a temperature of 2.73 K. What is the significance of the near-perfect match between the data and the theoretical spectrum?

It shows that the cosmic microwave background has a thermal radiation spectrum, just as the Big Bang theory predicts it should.

Each dot on this graph represents an individual Cepheid variable star. Which of the following is true for a Cepheid that is 10,000 times as luminous as the Sun?

It varies gradually in brightness, with a peak in brightness about every 30 days.

The arrow in the photo on the left points to the star that we see as a supernova in the photo on the right. What can we conclude about this star?

It was a high-mass star with at least 8 times the mass of the Sun.

This figure shows observations over more than a decade that have allowed us to determine the orbits of several stars around Sgr A* (the central object). What can we learn about Sgr A* by analyzing these orbits?

Its mass See image #14

What is the main idea captured by this graph?

Low-mass stars are much more common than higher-mass stars.

This graph is made from data measurements of the cosmic microwave background (dots) and a model based on the hypothesis of inflation. What does it show?

Measurements of the separation between regions of different temperature (in the cosmic microwave background) agree with predictions made by the hypothesis of inflation. See image #21

Which distance measurement technique is most suited to measuring objects at a distance of 10 light-years?

Parallax

This diagram represents an edge-on view of our Milky Way galaxy. Of the four labeled stars, which one could represent the Sun's position in the galaxy?

Position 1

This photo shows an object located in the halo of our Milky Way galaxy. Notice the many bright red dots in the photograph. What are they?

Red giant stars

This figure shows an all-sky map of the cosmic microwave background recorded by the Planck telescope. What do the dark and bright variations represent?

Regions of the sky with very slightly different density at the time the radiation was emitted.

What is the approximate lifetime of a star whose mass is 10 times that of the Sun?

Slightly longer than 10^7 years

Which of the following represents the true shape of a black hole as you'd see it (or measure it) as you flew past it in a spaceship?

Sphere

This diagram represents an edge-on view of our Milky Way galaxy. Of the four labeled stars, which one is located in what we call the halo of the galaxy?

Star 4

This image shows a colliding pair of galaxy clusters known together as the Bullet Cluster. The blue region represents a map of the cluster's dark matter. How was this blue map made?

The blue region was inferred from studies of how the cluster causes gravitational lensing of objects located behind it. (In image, larger cluster on left, smaller cluster on right)

All the stars in this photo are at about the same distance from Earth (some 25,000 light-years away). Which stars in this picture are the largest in size (radius)?

The bright red stars

This photograph shows an interstellar bubble about 10 light-years in diameter. If you could photograph this same region about 100 years from now, how would you expect it to look different?

The bubble will be slightly larger

This graph shows how the average distances between galaxies changes with time in the four models for the universe and also shows data points measured from white dwarf supernovae. Which of the following statements best describes what the data are telling us?

The data indicate that we live in an accelerating universe. See image #23

Study this diagram that summarizes the eras of the universe. Which of the following statements is not true?

The electroweak era was the longest lasting of all the eras in the history of the universe. See image #19

This sequence of paintings represents the formation of the Milky Way galaxy. What law of nature explains why the galaxy began to rotate rapidly and flatten out as it shrunk in size?

The law of conservation of angular momentum See image #13

This painting shows an accretion disk around a black hole in a close binary star system. What physical law explains why matter flowing from the companion star orbits rapidly as it nears the black hole?

The law of conservation of angular momentum See image #8

Study this graph, focusing on the red curve and reddish horizontal swath. Which statement that follows correctly interprets what the graph shows?

The measured abundance of deuterium agrees with the theoretically predicted abundance only if we make the prediction with a model of the universe in which ordinary matter makes up about 5% of the critical density.

This graph shows a gravitational wave signal recorded by the gravitational wave detectors (called LIGO) in two locations? What do models indicate was the cause of this signal?

The merger of two black holes in a distant galaxy

This famous image from the Hubble Space Telescope shows what is sometimes called the "pillars of creation." Which of the following best describes what it shows?

The pillars are clouds of gas and dust in which many new stars are forming; the edges of the pillars are sculpted by ultraviolet radiation from stars outside the pillars.

Notice the well-defined spiral arms in this photograph of the galaxy M51. What makes the spiral arms so much brighter than regions between the arms?

The presence of many massive young stars in the spiral arms.

This graph shows about 20 seconds of data from a pulsar. Based on current understanding of pulsars, what can we conclude?

The pulsar is a neutron star that makes one full rotation about every 1.34 seconds. See image #7

This image combines a visible light view of the galaxy Hercules A with an image showing radio wave emission (the reddish colors) in its vicinity. The likely explanation for the two huge clumps of radio emission far to either side of the visible galaxy is _________.

The radio emission comes from gas shot out into space by jets powered by a supermassive black hole in the galactic center

Why do some of the bright stars (such as the one indicated by the arrow) in this photo have cross-shaped spikes over them?

The spikes are an artifact of photography through a telescope.

Notice the distorted galaxy images, such as the large arc-shaped structure, in this image of a galaxy cluster. What can astronomers learn by carefully measuring the distortions in this image?

The total mass of the cluster

This graph shows the rotation curves of four different spiral galaxies. Based on these curves, what do all four galaxies have in common?

Their most distant stars all orbit at about the same speed as stars located about 30,000 light-years from their centers.

Which of the following is not implied by this diagram?

There are six distinct forces known to operate in the universe, and a seventh force called the "super force" might also exist.

This diagram shows several stages in a computer simulation of a collision between two galaxies. What happens?

Two spiral galaxies merge to become an elliptical galaxy surrounded by debris.

A spacecraft is on a trajectory that happens to be taking it near a black hole. Which diagram shows how the spacecraft's orbit will be affected?

Unbound trajectory See image #6

This photograph shows X-ray emission from a supernova remnant. What is the source of the X-rays?

Very hot gas expanding outward from the site of a supernova.

The image of X-ray emission uses different colors of light to represent different levels of brightness. The dark blue color represents the least bright X-ray emission. Which color represents the brightest X-ray emission?

White

The image of radio emission uses different colors of light to represent different levels of brightness. Which color represents the brightest radio emission?

White See image #11

Compare the radio and X-ray images. Can you conclude that gas clouds containing molecules absorb X rays?

Yes

What is the approximate size of the visible galaxy producing the jets?

about 200,000 light-years in diameter

What is the approximate distance from the far edge of one lobe to the far edge of the other?

approximately 2,100,000 light-years See image #16

Suppose a particular star has a core that is undergoing multiple stages of fusion simultaneously to give it the structure shown in this diagram. Based on your understanding of stellar lives, the mass of this star is __________.

greater than 8 times the mass of the Sun

Based on this diagram, "red sequence" galaxies are __________ than "blue cloud" galaxies.

redder and more luminous

What is the approximate lifetime of a star whose mass is 3 times that of the Sun?

slightly shorter than 10^9 years

Consider a spinning disk of pizza dough, as shown here. What would the rotation curve for the spinning dough look like?

straight line from bottom left to top right

On this graph, the time corresponding to the point at the far lower right of the diagonal line represents __________.

the age of the universe today, in seconds