Question 1

Why is the Hyades Cluster important for building up a catalog of the true luminosities of main- sequence stars?

Accepted Answer

The Hyades Cluster is important because it is one of the closest open star clusters to Earth, allowing astronomers to measure the distances to its stars using stellar parallax. This provides a reliable way to determine their true luminosities, which is crucial for calibrating the luminosities of main-sequence stars in general.

Question 2

This figure shows the Cepheid period- luminosity relation. What is the approximate luminosity of a Cepheid star that varies in brightness on a 10 day cycle?

Accepted Answer

The answer of  This figure shows the Cepheid period-...

Question 3

How does a lenticular galaxy differ from a normal spiral galaxy?

Accepted Answer

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Question 4

Which of the following phenomena are not thought to be results of collisions or other interactions between galaxies?

Accepted Answer

The fact that spiral galaxies have both disk and halo components is a fundamental characteristic of their structure, not directly a result of collisions or interactions with other galaxies. These components are thought to form through the process of galaxy formation and evolution, rather than through galactic interactions.

Question 5

What is a quasar?

Accepted Answer

A quasar is the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole.

Question 6

Molly measures a Hubble constant of 20 km/sec/million light- years. Sam measures a Hubble constant of 25 km/sec/million light- years. All other assumptions being the same, which person would estimate a LARGER age to the universe?

Accepted Answer

The Hubble constant (H) is inversely related to the age of the universe. A smaller Hubble constant implies a larger age for the universe. Since Molly measures a smaller Hubble constant (20 km/sec/million light-years) compared to Sam (25 km/sec/million light-years), Molly would estimate a larger age for the universe.

Question 7

Most active galactic nuclei are at large distances from us; relatively few nearby galaxies harbor active galactic nuclei. What does this imply?

Accepted Answer

Active galactic nuclei becoming less active as they age implies that we see more of them at large distances (and thus looking back in time) because they were more active in the past. Nearby galaxies, being observed in their current state, are less likely to have active nuclei if this activity diminishes over time.

Question 8

What is the most accurate way to determine the distance to a very distant galaxy?

Accepted Answer

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Question 9

What makes white- dwarf supernovae very good standard candles for distance measurements?

Accepted Answer

White-dwarf supernovae are excellent standard candles because they are both very bright, allowing them to be seen at vast distances, and they have a consistent luminosity, making it easier to calculate distances based on their observed brightness.

Question 10

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

Accepted Answer

Globular clusters are not a major category of galaxies, they are dense collections of stars orbiting around galaxies.

Question 11

Compared to spiral galaxies, elliptical galaxies are

Accepted Answer

Elliptical galaxies are generally redder in color due to their older populations of stars, whereas spiral galaxies typically have more young, blue stars. Elliptical galaxies also tend to have a more rounded shape than spiral galaxies.

Question 12

What is the current limit to distances we can measure via parallax, until the results of the new Gaia mission become available?

Accepted Answer

The current limit to distances we can measure via parallax is about 1000 light years, which means that we cannot accurately measure the distances of objects beyond that distance using parallax. The upcoming Gaia mission is expected to greatly improve our ability to measure distances using parallax, extending the limit to tens of thousands of light years.

Question 13

Dr. X believes that the Hubble constant is H0 = 20 km/s/Mly while Dr. Y believes it is H0 = 24 km/s/Mly. Which statement below automatically follows?

Accepted Answer

The Hubble constant (H0) is a measure of the rate of expansion of the universe. A lower value of H0 implies a slower rate of expansion, which in turn suggests that the universe has been expanding for a longer period of time. Therefore, if Dr. X believes H0 = 20 km/s/Mly, which is lower than Dr. Y's belief of H0 = 24 km/s/Mly, it follows that Dr. X believes the universe is older than Dr. Y does.

Question 14

Which of the following phenomena is probably not related to the presence of a supermassive black hole?

Accepted Answer

The presence of globular clusters in the halos of galaxies is not directly related to the presence of a supermassive black hole. While the dynamics of globular clusters can be affected by the mass distribution of the galaxy, the presence of a black hole is not necessary for their existence or behavior. The other choices (B, C, and D) are all phenomena that are commonly associated with the presence of a supermassive black hole.

Question 15

Which of the following processes slowed the collapse of protogalactic clouds?

Accepted Answer

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Question 16

Recall that a raisin cake is sometimes used to imagine how an expanding universe behaves. Suppose you are in a uniformly expanding raisin cake, sitting on Raisin A, looking at Raisin B, 2 cm away from you. Raisin B is moving away from you at 1 cm/sec. At the same time, you observe another Raisin C, which is moving away from you at 3 cm/sec. How far away is Raisin C from Raisin A?

Accepted Answer

In the expanding raisin cake model, the distance between any two raisins increases proportionally to their initial distance. Therefore, the ratio of the distances between raisin A and B and raisin A and C will remain constant over time. We can set up the following proportion:

distance between A and B : distance between A and C = 2 cm : x

where x is the distance between A and C. We know that raisin B is moving away from us at 1 cm/sec, so after time t, the distance between A and B will be 2 + t cm. Similarly, the distance between A and C will be x + 3t cm. Therefore, we can set up another proportion:

(2 + t) cm : (x + 3t) cm = 2 cm : x

Cross-multiplying and simplifying, we get:

2x + 6t = 2(x + 3t)
2x = 6t
x = 3t

So the distance between raisin A and C is always three times the distance between raisin A and B. Therefore, if raisin B is currently 2 cm away from raisin A, raisin C must be 6 cm away from raisin A. The answer is C).

Question 17

Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?

Accepted Answer

The observation that most active galactic nuclei (AGN) are found at large distances, and thus we see them as they were in the past due to the time it takes light to travel, suggests that AGNs tend to become less active over time. This is because we see fewer AGNs nearby, implying they were more common in the earlier universe and have since become less active or quiescent.

Question 18

Use the graph above showing data for the brightest galaxies in clusters of galaxies to answer the following questions. Which statement describes this graph?

Accepted Answer

The graph likely shows a trend where the more distant galaxies appear redder, which is consistent with the redshift phenomenon observed in distant galaxies due to the expansion of the universe. The mention of exceptions acknowledges that not all galaxies will perfectly follow this trend due to various factors such as intrinsic properties of the galaxies or observational anomalies.

Question 19

Approximately how many stars does a dwarf elliptical galaxy have?

Accepted Answer

Dwarf elliptical galaxies typically have less than a billion stars.

Question 20

How many more stars does a starburst galaxy form, in one year, than the Milky Way?

Accepted Answer

A starburst galaxy can form about a hundred times more stars in a year compared to the Milky Way.

Quiz 16: A Universe of Galaxies