AST EXAM 2

Which of the following statements about an open cluster is true?

Which of the following statements about a globular cluster is true?

Cluster ages can be determined from

What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?

Which of these star clusters is oldest?

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

Where are large dust clouds predominantly located in the galaxy M51?

Where are the ionization nebulae predominantly located in the galaxy M51?

Why are the ionization nebulae so bright?

Compared with our Sun, most stars in the halo are

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

Where are most heavy elements made?

What do astronomers consider heavy elements?

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

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

What makes up the interstellar medium?

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

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?

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

What type of galaxy is M82 based on its appearance in the visible-light view?

Look again at the visible-light view of M82. What is the source of the white and blue light that dominates the image?

The infrared image of M82 shows a whitish-blue region running down the center, along with a much larger red region. What is emitting the light that is shown in red, and what is emitting the light that is shown in whitish-blue?

Study all of the individual images and the Multi image that combines all of them. Which of the following statements provides the best interpretation of what we see in the Multi image?

What can we conclude about this galaxy from the fact that there are so many supernovae occurring?

As you learned in Part E, galaxy M82 has unusually active star formation. Why do astronomers think that this is a "burst" of star formation, rather than thinking that this galaxy always has such a high rate of star formation?

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

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?

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?

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?

Which of the following types of galaxies are most commonly found in large clusters?

What is the major difference between an elliptical galaxy and a spiral galaxy?

Most large galaxies in the universe are

Which types of galaxies have a clearly defined halo component?

Which types of galaxies have a clearly defined disk component?

Which of the following types of galaxies are reddest in color?

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

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?

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?

What is a quasar?

Which of the following is not true of quasars?

Which of the following is evidence for supermassive black holes in active galaxies?

The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?

How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?

All of the following are true. Which of these gives evidence that quasars were more common in the early stages of the universe?

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

The best evidence for the existence of supermassive black holes is

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

The primary source of a quasar's energy is

How do we know that there are intergalactic clouds between a distant quasar and us?

The horizontal axis of the graph measures the time since the Big Bang in seconds. The extreme left of the horizontal axis, where it meets the vertical axis, is labeled 10−45 seconds (that is a decimal point followed by 44 zeroes and then a one). If we move along two tick marks to the right on the horizontal axis, it is labeled 10−35 seconds. By what factor does the time increase from one tick mark on the horizontal axis to the next tick mark toward the right?

The vertical axis of the graph measures the temperature of the universe in kelvin. If we move up one tick mark to the next, by what factor does the temperature increase?

In basic terms, what does the graph show?

To get your bearings on the horizontal time axis of this plot, it is useful to calculate the age of the universe in seconds today. If you multiply the age of the universe in years by the number of seconds in a year, approximately what is the current age of the universe in seconds?

Suppose you want to know what the temperature of the universe was 1 billion years ago. Where along the horizontal axis should you look?

What was the approximate temperature of the universe when the universe was just 1 second old?

From Part C, you know that in basic terms, the graph shows that the temperature of the universe decreases with time. In more specific terms, this graph shows that the temperature of the universe

During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?

Which of the following important events occurred earliest in the history of the universe?

During the history of the universe, what important event occurred about 380,000 years after the Big Bang?

Essentially all the hydrogen nuclei that will ever exist in our universe were created

Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is

Consider this statement from Part A: "Photons of the cosmic microwave background have traveled through space for almost 14 billion years." This statement follows from our model of the Big Bang, because the Big Bang model is based on the idea that

One of the inferred statements from Part A is that "Large-scale structure grew around density variations present in the early universe." Observational evidence that such density variations really existed comes from the fact that the cosmic microwave background exhibits

The Big Bang theory is closely linked to Hubble's discovery that the universe is expanding, which seems to imply that there was a time in the past when the expansion first began. Nevertheless, the Big Bang theory did not gain widespread acceptance among scientists until the 1960s. Why wasn't expansion alone enough to convince scientists that the Big Bang really happened?

Today, most scientists accept the Big Bang theory because its predictions agree so well with observations. But a scientific theory can always be revised or discarded if future observations do not agree with its predictions. Consider the following hypothetical future observations. Which one(s) would be inconsistent with the Big Bang theory?

Suppose there is a large amount of (weakly interacting) dark matter between us and a distant galaxy. How will this affect our view of the distant galaxy?

Examine the visible light image of the Bullet Cluster. What kind of cluster is it?

Study the composite image of the Bullet Cluster, as well as the animations. What do the two large, red-colored regions in the composite image represent?

There are also two large blue-colored regions in the composite image. These blue regions are labeled as "dark matter" based on

From Parts A though C, you should understand the three major components shown in the composite Bullet Cluster image. Notice that the hot, X-ray-emitting gas (red) is not in the same place as most of the visible galaxies and most of the matter (blue). How do we think the hot gas came to be in a different place from the galaxies and most of the matter?

Careful measurements show that the hot, X-ray-emitting gas in the Bullet Cluster contains about 7 times as much total mass as all the stars in the cluster's galaxies combined. Therefore, the fact that the most of the gravity is in the blue regions that surrounds the visible galaxies, rather than in the regions with the hot gas, indicates that

As noted in the Introduction, some scientists have proposed that dark matter does not really exist. According to this view, all matter is ordinary (baryonic), but at large distances from matter, gravity does not precisely obey either Newton's or Einstein's theories of gravity. Is this alternative view of gravity consistent with what we observe in the Bullet Cluster? Why or why not?

Consider a distant galaxy located directly behind a cluster of galaxies, as shown in this interactive figure. As seen from Earth, the gravitationally lensed images of the distant galaxy will appear more widely separated if the intervening cluster of galaxies has

Which of the following best explains why a higher-mass cluster of galaxies causes light from a distant galaxy to bend more than a lower-mass cluster of galaxies?

Consider a distant galaxy located directly behind a cluster of galaxies as shown in this interactive figure. Knowing the distance to the cluster of galaxies and the angular separation of the lensed images of the distant galaxy, astronomers can estimate:

The Rotation Curve for a Merry-Go-Round animation shows a rotating merry-go-round. Click several points on the merry-go-round, and watch the corresponding points appear on the graph below it. This graph is what we call a rotation curve, because it plots the speed at which any point rotates around the center (the orbital speed) against the distance of that point from the center. Based on the graph, you can conclude that doubling the distance of a point from the center of the merry-go-round would

Now, let's turn our attention to rotation curves for orbiting masses which are not rigidly held together like the points on a merry-go-round. The Rotation Curve of the Solar System animation shows the orbits of Mercury, Venus, Earth, and Mars. Click on each of the orbits, and watch the corresponding points appear on the graph below it. If a planet (or asteroid) orbited the Sun at three times the distance of Mars, its orbital speed would be

Why does the rotation curve for the solar system show speeds that become slower with increasing distance from the Sun?

Open the Rotation Curve of a Spiral Galaxy animation and click at various distances from the galactic center to create a graph of the galaxy's rotation curve; be sure to start with points very close to the galactic center and continue to well beyond the visible part of the galaxy. Which of the following statements best describes the pattern of the graph?

To understand why the galaxy rotation curve in Part D is flat, we must first understand how gravity determines the orbital speeds of stars around the galactic center. Consider any star on a circular orbit around the center of the galaxy. The speed of the star's orbit depends on the star's distance from the galactic center and

From Part D, you know that the galaxy's rotation curve is nearly flat, even well beyond the point at which we see any stars in the galaxy. According to the law of gravity as we understand it today, the only explanation for these this flatness is that

In (Figure 1) at left, which of the four labeled supernovae is the most distant from us?

Which of the models predict that galaxies should be getting farther apart now? (Keep in mind that now is located at at time=0years on the graph.)

Which of the models predict that galaxies will eventually get closer together in the future?

Which model predicts the largest average distance between galaxies 6 billion years ago?

Which model is most clearly ruled out by the data on the graph?

Which model is most strongly supported by the data on the graph?

Each data point represents a single white dwarf supernova that has been observed. The data points that appear farthest to the left on the graph represent the white dwarf supernovae that are the

What additional data would be most valuable in helping scientists evaluate whether the accelerating model really is the best of the four models?

The idea that life evolves through time was first suggested in ancient Greece, and it was favored by at least some scientists of the 18th and 19th centuries even before Charles Darwin proposed the theory of evolution. What is the key observational evidence that supports the idea that life on Earth has evolved through time?

Given that the fossil record provides the key evidence for evolution, what is the importance of Darwin's theory of evolution?

The first of the two "undeniable facts" is that any localized population of a species has the potential to produce far more offspring than the local environment can support. This fact is important to understanding evolution because it means that

The second of the two "undeniable facts" is that individuals in a population of any species vary in many heritable traits (traits passed from parents to offspring), so that no two individuals are exactly alike. This fact is important to understanding evolution because it means that

The two facts from Parts C and D lead to the "inescapable conclusion" that individuals in a population will have unequal reproductive success, so that those whose traits best enable them to survive will leave more offspring. Therefore, in any local environment, over time

The theory of evolution by natural selection gained rapid acceptance among biologists after Darwin published it in 1859, in part because it was so successful in explaining what we see in the fossil record. The theory of evolution has gained even further support since that time, because it has successfully passed many other observational tests. Which of the following statements represent successful tests of the theory of evolution by natural selection?

Like any scientific theory, the theory of evolution is subject to revision or even to being discarded if future observations do not agree with its predictions. Which of the following hypothetical observations (none of which are real) would force us to reconsider the theory of evolution?

Earth was born about 4.5 billion years ago. According to current estimates, approximately how long after Earth's formation did the Moon form?

The oldest fossil evidence of life dates to about __________ ago.

Dinosaurs went extinct, probably because of an impact, about __________ ago.

As the mass of the central star increases, the distance to the habitable zone __________ and the size (width) of the habitable zone

Suppose that our Sun was cool enough to include Mercury in its habitable zone. Which of the following would be true in that case?

Scientists think it is very unlikely that complex and large forms of life could evolve on planets that orbit stars that are much more massive than the Sun. Why?

Which statement explains the observations that make it seem possible that Mars could have life underground?

In Part A you found that the terrestrial planet 10 AU from a 0.5MSun star is unlikely to be habitable. Could this planet be habitable if it were in a different orbit around its star?

To make sure you understand how to use the equation, suppose that there are 1000 habitable planets in our galaxy, that 1 in 10 habitable planets has life, that 1 in 4 planets with life has at some point had an intelligent civilization, and that 1 in 5 civilizations that have ever existed is in existence now. How many civilizations would exist at present?

Based on current science which of the following is the most reasonable range for possible values of the number of habitable planets, NHP, in our galaxy?

Suppose that life is very common on habitable worlds, meaning that life tends to get started on almost any world that has conditions that allow for life (such as surface liquid water). Which would then be true about the terms in the Drake equation?

Which of the following would tend to make the term fnow small (close to 0)?

What defines the habitable zone around a star?

How does the habitable zone around a star of spectral type G compare to that around a star of spectral type M?