Mastering Astronomy chap. 11

You discover a new cluster of galaxies, and the brightest galaxy in this new cluster has an infrared color ratio of 0.65. Based on the data in the graph, what is the approximate distance to this new cluster? PART B

1 billion light-years

Suppose a collision strips gas out of a spiral galaxy. Why would this tend to change the spiral galaxy into an elliptical galaxy? PART B

A galaxy cannot have a disk if it does not have gas.

Why do astronomers hypothesize that a massive black hole lies at the center of M87? PART A

A very small region at the center of M87 releases an enormous amount of energy.

This painting represents the Milky Way Galaxy as it might appear from a distance. Identify the indicated features. PART A

Top to bottom: spiral arm bulge disk

A follow-up study showed that the galaxies that are exceptions to the general trend on the original graph have unusually brighter centers; that is, these galaxies contain active galactic nuclei. Based on this follow-up study, could you improve your confidence in your distance estimate for the new cluster discussed in Part B, and, if so, how? PART C

Yes, by photographing the new cluster with better angular resolution to see whether its brightest galaxy has an unusually bright center.

What kind of object do we think lies in the center of the Milky Way Galaxy?

a 3 to 4 million solar mass black hole

Listed following are several locations in the Milky Way Galaxy. Rank these locations based on their distance from the center of the Milky Way Galaxy, from farthest to closest. PART A

a globular cluster in the outskirts of the halo a cloud of gas and dust in the outskirts of the disk our solar system the edge of the central bulge

The luminosity of a quasar is generated in a region the size of

a solar system

Imagine a photon of light traveling the different paths in the Milky Way described in the following list. Rank the paths based on how much time the photon takes to complete each journey, from longest to shortest. PART B

across the diameter of the galactic halo across the diameter of the galactic disk from the sun to the center of the galaxy across the diameter of the central bulge through the disk from top to bottom

Which of the following statements correctly summarize key differences between the disk and the halo? PART D

all of them

Why do disk stars bob up and down as they orbit the galaxy?

because the gravity of other disk stars always pulls them toward the disk

Which of the following is NOT one of the three major categories of galaxies?

globular galaxies

The primary source of a quasar's energy is

gravitational potential energy

The very first stars in the universe were made of

hydrogen and helium.

Where does most star formation occur in the Milky Way Galaxy?

in the spiral arms

Which forms of light are lower in energy and frequency than the light that our eyes can see?

infrared and radio

Current understanding holds that a galaxy's type (spiral, elliptical, or irregular) ______.

may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies

This painting represents the Milky Way Galaxy as it would appear edge-on from a distance. Label the indicated features; be sure to pay attention to where the leader lines are pointing. PART B

top, left to right: globular clusters bulge halo both bottom are disk

Each item below belongs either with the population of disk stars or the population of halo stars of the Milky Way Galaxy. Match each item to the appropriate population.

Disk stars (yellow): youngest stars the sun stars that all orbit in nearly the same plane high-mass stars Halo stars (green): stars with the smallest abundance of heavy elements stars whose orbits can be inclined at any angle oldest stars globular clusters

Click the icon "Spiral arm and star motion" in the interactive figure and watch the animation of the galaxy's rotation over several hundred million years. Which of the following statements accurately describe the motion? PART B

Individual stars orbit around the center of the galaxy. Individual stars move in and out of spiral arms over time.

What do we mean by the star-gas-star cycle?

It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.

Sort each item into the appropriate bin according to whether it is more common in spiral arms or about equally common within and between the spiral arms in a spiral galaxy's disk. PART A

More common in spiral arms: young stars ionization nebulae star formation dense, dusty gas clouds Equally common within and between spiral arms: old stars

Which statement describes the trend among the galaxies shown on this graph? PART A

More distant galaxies tend to have a larger infrared color ratio, but there are some exceptions.

Different regions of the galaxy tend to contain stars of different ages. Place labels for the ages of stars in the correct regions of the galaxy painting. PART C

Outer: mostly very old stars Inner: both old and young stars

Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once.

1. The circular but relatively flat portion of the galaxy is the disk. 2. The first portion of the galaxy to form was the halo. 3. A tightly packed group of a few hundred thousand very old stars is a globular cluster. 4. A spiral arm stands out in a photo of a galaxy because it shines brightly with light from massive young stars and glowing clouds of gas and dust. 5. Our Milky Way galaxy is a spiral galaxy. 6. Stars orbiting in the bulge near the galaxy's center can have orbits highly inclined to the galactic plane.

Match the terms in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each term only once.

1. The globular cluster M13 belongs to the halo component of the Milky Way Galaxy. 2. A(n) elliptical galaxy contains hot, ionized gas but very little cool gas or dust. 3. The type of galaxy known as a(n) irregular galaxy was more common in the universe 10 billion years ago. 4. The Milky Way is a(n) spiral galaxy. 5. Our Sun belongs to the disk component of the Milky Way Galaxy. 6. Scientists investigating cosmology study how the distribution of galaxies changes with time.

Astronomers suspect that a galaxy's type can be determined either by initial conditions in a protogalactic cloud or by later interactions between galaxies. Each item below describes either an initial condition or a later interaction. Match these items to the galaxy type expected to form as a result.

Elliptical galaxy: stars for rapidly as the protogalactic cloud shrinks protogalactic cloud has high density a galaxy collision strips away gas protogalactic cloud rotates very slowly Spiral galaxy: protogalactic cloud has high angular momentum most protogalactic gas settles into a disk

Astronomers suspect that a galaxy's type can be affected both by the conditions in the protogalactic cloud from which it forms ("initial conditions") and by later interactions with other galaxies. Each item below describes either a condition in a protogalactic cloud or a later interaction. Match these items to the galaxy type you would expect to form as a result. PART A

Elliptical galaxy: stars form rapidly as the protogalactic cloud shrinks protogalactic cloud has high density a galaxy collision strips away gas protogalactic cloud rotates very slowly Spiral galaxy: most protogalactic gas settles into a disk protogalactic cloud has high angular momentum

High angular momentum leads to faster rotation. Why does faster rotation tend to lead to a spiral galaxy, rather than an elliptical galaxy? PART D

Faster rotation leads to collisions among gas particles that cause the gas to settle into a spinning disk, rather than a more spread out cloud.

Consider both the original study (with data shown on the graph) and the follow-up study showing that the exceptions to the general trend are galaxies with unusually bright centers (as described in Part C). Which of the following conclusions are supported by this pair of studies? PART D

Galaxies with unusually bright nuclei are more common at greater distances. On average, more distant galaxies have larger infrared color ratios. Galaxies with unusually bright nuclei were more common when the universe was young than they are today.

Assuming that the bright core of M87 is powered by a supermassive black hole, which of the following best describes the source of energy that makes the core appear so bright? PART C

Gravitational potential energy is converted to thermal energy as matter from the surrounding gas disk spirals into the central black hole.

High density tends to lead to more rapid star formation in a protogalactic cloud. Why does this rapid star formation tend to lead to an elliptical galaxy, rather than a spiral galaxy? PART C

Rapid star formation means that there may not be enough gas left to make a disk.

Watch the video that comes up when you click the icon "Star formation in spiral arms" in the interactive figure. Which of the following best describes what spiral arms are? PART C

Spiral arms are waves of higher density that move outward through a galaxy, triggering star formation as they pass.

The third image in the video (with the most detailed view of the galactic center) is labeled "gas disk." Which of the following best describes what we are seeing in this photo? PART B

The black hole is located deep within the bright central region, and around this region we see gas that is orbiting the central black hole.

Based on observations, which of the following statements about stars in the Milky Way is generally true?

The older the star, the lower its abundance of heavy elements.

What do halo stars do differently from disk stars?

They orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane.