Chap 27 and 28

Question 1

Describe some differences between quasars and normal galaxies.

Answer 1

1

Question 2

Describe the arguments supporting the idea that quasars are at the distances indicated by their redshifts.

Answer 2

2

Question 3

Why could the concentration of matter at the center of an active galaxy like M87 not be made of stars?

Answer 3

4

Question 4

Why do astronomers believe that quasars represent an early stage in the evolution of galaxies?

Answer 4

7

Question 5

What evidence do we have that the luminous central region of a quasar is small and compact?

Answer 5

11

Question 6

Suppose you observe a star-like object in the sky. How can you determine whether it is actually a star or a quasar?

Answer 6

12

Question 7

Why don’t any of the methods for establishing distances to galaxies, described in Galaxies (other than Hubble’s law itself), work for quasars?

Answer 7

13

Question 8

One of the early hypotheses to explain the high redshifts of quasars was that these objects had been ejected at very high speeds from other galaxies. This idea was rejected, because no quasars with large blueshifts have been found. Explain why we would expect to see quasars with both blueshifted and redshifted lines if they were ejected from nearby galaxies.

Answer 8

14

Question 9

Show that no matter how big a redshift (z) we measure, v/c will never be greater than 1. (In other words, no galaxy we observe can be moving away faster than the speed of light.)

Answer 9

20

Question 10

If a quasar has a redshift of 3.3, at what fraction of the speed of light is it moving away from us?

Answer 10

21

Question 11

The quasar that appears the brightest in our sky, 3C 273, is located at a distance of 2.4 billion light-years. The Sun would have to be viewed from a distance of 1300 light-years to have the same apparent magnitude as 3C 273. Using the inverse square law for light, estimate the luminosity of 3C 273 in solar units.

Answer 11

29

Question 12

How are distant (young) galaxies different from the galaxies that we see in the universe today?

Answer 12

1

Question 13

What is the evidence that star formation began when the universe was only a few hundred million years old?

Answer 13

2

Question 14

Describe the evolution of an elliptical galaxy. How does the evolution of a spiral galaxy differ from that of an elliptical?

Answer 14

3

Question 15

Explain what we mean when we call the universe homogeneous and isotropic. Would you say that the distribution of elephants on Earth is homogeneous and isotropic? Why?

Answer 15

4

Question 16

What is the evidence that a large fraction of the matter in the universe is invisible?

Answer 16

6

Question 17

When astronomers make maps of the structure of the universe on the largest scales, how do they find the superclusters of galaxies to be arranged?

Answer 17

7

Question 18

Describe how you might use the color of a galaxy to determine something about what kinds of stars it contains.

Answer 18

9

Question 19

Suppose you are standing in the center of a large, densely populated city that is exactly circular, surrounded by a ring of suburbs with lower-density population, surrounded in turn by a ring of farmland. From this specific location, would you say the population distribution is isotropic? Homogeneous?

Answer 19

15

Question 20

Human civilization is about 10,000 years old as measured by the development of agriculture. If your telescope collects starlight tonight that has been traveling for 10,000 years, is that star inside or outside our Milky Way Galaxy? Is it likely that the star has changed much during that time?

Answer 20

17