Astronomy Final Homework – Flashcards
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Where are most of the Milky Way's globular clusters found?
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In the halo
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How do we determine the Milky Way's mass outside the Sun's orbit?
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From the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun
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Which kind of star is most likely to be part of the spheroidal population?
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an M star
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The best measurements of the mass of the black hole at the galactic center come from
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The orbits of stars in the galactic center.
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Suppose you observe a star orbiting the galactic center at a speed of 1300 km/s in a circular orbit with a radius of 21 light-days. What would your estimate be for the mass of the object that the star is orbiting?
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6.93×10^6 MSun
(1.3*10^+6)^2 * (5.439*10^+14) / (6.67*10^-11)
Ans / (1.98*10^30)
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Which of these galaxies would you most likely find at the center of a large cluster of galaxies?
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A large elliptical galaxy
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Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?
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A white dwarf supernova
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Why do virtually all the galaxies in the universe appear to be moving away from our own?
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Because expansion causes all galaxies to move away from nearly all others.
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The primary source of a quasar's energy is
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Gravitational potential energy.
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Imagine that you have obtained spectra for several galaxies and have measured the redshift of each galaxy to determine its speed away from us. Here are your results:
Galaxy 1: Speed away from us is 15000 km/s.
Galaxy 2: Speed away from us is 20000 km/s.
Galaxy 3: Speed away from us is 25000 km/s.
Estimate the distance to each galaxy from Hubble's law. Assume that H0=22km/(sMly).
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(speed away from us) / (22 km/s/Mly)
rGalaxy1 = 680 million light years
rGalaxy2 = 910 million light years
rGalaxy3 = 1100 million light years
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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?
What are we seeing in this photograph?
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About the size of a grain of sand held at arm's length against the sky
Almost every object in the photo is a galaxy, and these galaxies are at many different distances from us.
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Is this a photo of a spiral galaxy or an elliptical galaxy, and how do you know?
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It is a spiral galaxy, because we can see a dusty disk going across the center.
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This photo shows the Large Magellanic Cloud, or LMC for short. Based on what you have learned in about the LMC from your textbook, which of the following statements about the LMC is not true?
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Galaxies similar to the LMC are very rare.
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This photo shows the central region of a cluster of galaxies. Based on what you have learned from your textbook, which of the following statements about this photo is not true?
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The oldest stars in these galaxies are much older than the oldest stars in our own Milky Way.
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What is this a picture of?
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A cluster of galaxies
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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?
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It varies gradually in brightness, with a peak in brightness about every 30 days.
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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:
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Hubble's law
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This diagram shows several stages in a computer simulation of a collision between two galaxies. What happens?
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Two spiral galaxies merge to become an elliptical galaxy surrounded by debris.
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Based on this diagram, "red sequence" galaxies are __________ than "blue cloud" galaxies.
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Redder and more luminous
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Suppose that Hubble's constant were 11 km/s/million light years instead of 22 km/s/million light years. How would this graph look different?
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The data would follow a more shallow line, closer to horizontal than the current line.
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This a radio image of the galaxy Cygnus A, with the visible image of the galaxy shown in the inset. The likely explanation for the two huge clumps of radio emission far to either side of the visible galaxy is:
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The radio emission comes from gas shot out into space by jets powered by a supermassive black hole in the galactic center.
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The white arrow points to an object that lies within the disk of the galaxy shown. What is this object?
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A supernova
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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?
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About the size of our solar system
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This figure is a spacetime diagram, which means it shows space (distance in this case) on the horizontal axis and time on the vertical axis. Study it carefully to be sure you understand it. Now, look at the square around one of the galaxy images. What does the position of this image mean on this diagram?
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It indicates that the galaxy was closer to the Milky Way when the supernova exploded 400 million years ago.
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The current temperature of the universe as a whole is
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A few K.
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When a proton and an antiproton collide, they
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Convert into two photons.
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Which of the following does inflation help to explain?
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The uniformity of the cosmic microwave background
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Which of these pieces of evidence supports the idea that inflation really happened?
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Observations of the cosmic microwave background that indicate a flat geometry for the universe
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Which of these options is the best explanation for why the night sky is dark?
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The universe is not infinite in space.
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Dark matter is inferred to exist because:
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We can observe its gravitational influence on visible matter.
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Measurements of how orbital speeds depend on distance from the center of our galaxy tell us that stars in the outskirts of the galaxy
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Orbit the galactic center just as fast as stars closer to the center.
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A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of what astronomers call:
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A gravitational lens.
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Based on current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies?
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Subatomic particles that we have not yet detected
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Which of the following possible types of universe would not expand forever?
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A recollapsing universe
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Consider a spinning disk of pizza dough, as shown here. What would the rotation curve for the spinning dough look like?
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Straight positive line
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This graph shows the rotation curves of four different spiral galaxies. Based on these curves, what do all four galaxies have in common?
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Their most distant stars all orbit at about the same speed as stars located about 30,000 light-years from their centers.
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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?
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Gravitational lensing
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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?
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The total mass of the cluster
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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?
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The blue region was inferred from studies of how the cluster causes gravitational lensing of objects located behind it.
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Study this graph, focusing on the red curve and reddish horizontal swath. Which statement below correctly interprets what the graph shows?
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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 4% of the critical density.
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This figure shows a "slice of the universe" from the Sloan Digital Sky Survey. What is the Sloan Great Wall (indicated by the arrow)?
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A huge collection of galaxies extending a billion light-years in length
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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?
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Accelerating universe
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These diagrams represent four possible models for the universe. Which model presumes the existence of some type of dark energy in the universe?
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Accelerating universe
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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?
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The data indicate that we live in an accelerating universe.
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Fossil evidence suggests that life on Earth arose
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Within a few hundred million years after Earth formed
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The theory of evolution is
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A scientific theory, meaning that it is backed by extensive evidence.
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According to current understanding, the key requirement for life is
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Liquid water.
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How does the habitable zone around a star of spectral type G compare to that around a star of spectral type M?
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It is larger.
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Suppose there are 1.10×104 civilizations broadcasting radio signals in the Milky Way Galaxy right now.
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On average, how many stars would we have to search before we would expect to hear a signal? Assume there are 500 billion stars in the galaxy.
N1 = 4.55×107
How does your answer change if there are only 120 civilizations instead of 1.10×104?
N2 = 4.17×109
