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Homework Terms in this set (96)... ... If the orbital distance of Earth was greater than its actual value, the parallax angle to nearby stars would be ___________. higher If the orbital distance of Earth was greater than its actual value, the maximum distance a star could be away from Earth for its distance to be determined using the parallax method (with current telescopes) would be _________. higher than the actual upper limit Stars that have the highest apparent brightness are ________. nearby and very luminous Massive-star supernovae are not good standard candles because ___________. they have different luminosities (since they have different masses) What two things are needed to determine a standard candle's distance from Earth? apparent brightness and luminosity About how long would it take for a radar pulse to travel round trip from Earth to Neptune and back again to Earth? 8 hours A supernova is observed in a galaxy 2,000 million light-years away. How long ago did the supernova occur? 2 billion (giga) years ago Which type of standard candle is the most appropriate for determining the distance to nearby galaxies (like the Andromeda Galaxy)? Cepheid variables Which of the following is the least accurate method for determining cosmic distances? Hubble's Law Astronomers believe that nearly all galaxies are moving away from us because _________. the space in between the galaxies is expanding Current estimates place the value of Hubble's constant (H0) near 22 km/s/Mly, giving 14 billion years as the age of the universe. If H0 were in fact 44 km/s/Mly, the approximate age of the universe would be _____________. half as much Suppose Hubble's constant is H0 = 22 km/s/Mly. Then we would expect a galaxy located 10 million light-years (Mly) away to be moving away from us at a speed of about _______________. 220 km/s An astronomer looking out into space will observe that _______. the farther out a galaxy is from Earth, the faster it is moving away From our vantage point in the Milky Way, we see distant galaxies all moving away from us and more distant ones moving faster. Suppose you lived in a distant galaxy, what would you observe? The same rule that we observe: all galaxies moving away from you, and more distant ones moving faster. One reason Hubble's constant isn't exactly known today is ______. the exact distance of a galaxy is difficult to measure Hubble's law shows that galaxies with high speeds as measured from Earth are __________. moving away from Earth and are farther from Earth than galaxies with lower speeds What can we say about the galaxies that have the lowest speeds? They are moving away from Earth and are closer to Earth than galaxies with high speeds. Suppose that galaxy B is twice as far from Earth as galaxy A. Hubble's law predicts that galaxy B will be moving away from Earth with approximately _____. twice the velocity of galaxy A Hubble's law (the straight-line fit to the data) predicts that a galaxy's recession velocity is proportional to its distance from Earth. Hubble's law therefore predicts that a galaxy twice as far away moves at twice the speed, a galaxy three times as far away moves at three times the speed, and so on. Imagine that when we looked out into the universe we found that the light from all galaxies was blueshifted (rather than redshifted) and that the light from the most distant galaxies was blueshifted by the greatest amount. Which statement best describes what we would conclude about the motions of galaxies in this case? All are moving toward Earth, with distant galaxies moving faster than nearby galaxies. In this hypothetical case, all the galaxies would be rushing toward Earth, with the more distant galaxies approaching at the fastest pace. This would tell us we lived in a collapsing universe rather than an expanding one. The age of the universe is related to the slope of the graph of Hubble's law, and current data put the age of the universe at about 14 billion years. Suppose that future observations showed that the slope of Hubble's law on the graph is actually steeper than that shown. In that case, the age of the universe would be _________ than 14 billion years because the universe is expanding ______ than current data suggest. younger/more rapidly A more steeply sloped line for Hubble's law would indicate faster speeds for galaxies at all distances, which would mean a faster rate of expansion. And a faster rate of expansion means it has taken less time since the Big Bang for the universe to reach its present size. In other words, a steeper slope (which means a larger value of Hubble's constant) means a younger and more rapidly expanding universe. [Note]: Recall that a redshift tells us that an object is moving away from us, and the larger the redshift, the higher the speed. Note that expansion applies to the whole universe, so astronomers tend to think of galaxies being carried along with the expansion rather than moving "through" the universe. For this reason, redshifts due to expansion are often called "cosmological redshifts." *** [Note]: If you look at the speed corresponding to a distance of 400 million light-years on each graph, you will see that the speed declines in the order shown. Note also that this ranking puts the graphs in order of declining steepness. In other words, a steeper slope for Hubble's law would predict faster speeds for galaxies at particular distances. *** Because galaxies all started out close together (early in the history of the universe), higher speeds would mean that they would have reached their current distances in less time — and less time means a younger universe. In other words, the steeper the graph for Hubble's law, the more rapid the rate of expansion (a higher value of Hubble's constant), and the more rapid the rate of expansion the younger the universe. *** Some things to know about Universe Expansion (1) The universe as a whole is expanding, but gravitationally bound objects such as galaxies are not expanding with time. (2) Notice that the galaxies that started farther away (on the small balloon) traveled greater distances as the balloon expanded (3) The farther away a galaxy is from your galaxy, the faster it will be moving away from you. This simple statement embodies the idea behind Hubble's law. (4) The location of your galaxy does not matter: The speed at which the other galaxy is moving away from you depends only on its distance, with more distant galaxies moving faster in accord with Hubble's law. Hubble's law expresses a relationship between __________. the distance of a galaxy and the speed at which it is moving away from us We can always determine the recession velocity of a galaxy (at least in principle) from its redshift. But before we can use Hubble's law, we must first calibrate it by __________. measuring the distances to many distant galaxies with a standard candle technique Suppose that you measure a galaxy's redshift, and from the redshift you determine that its recession velocity is 30,000 (3×104) kilometers per second. According to Hubble's law, approximately how far away is the galaxy? 1.4 billion light years Based on what you have learned, which of the following best describes the meaning of Hubble's constant (H0 )? It describes the expansion rate of the universe, with higher values meaning more rapid expansion. The larger the value of Hubble's constant, the faster galaxies are being carried away from us with the expansion of the universe. For example, if a galaxy's velocity depended only on the expansion of the universe, then a galaxy that is 1 million light-years away would have a recession velocity of 22 kilometers per second, a galaxy 10 million light-years away would have a recession velocity of 220 kilometers per second, and a galaxy 100 million light-years away would have a recession velocity of 2200 kilometers per second. In other words, Hubble's constant essentially tells us the expansion rate of the universe, since it tells us how fast galaxies are moving at different distances away from us. A higher value of Hubble's constant would mean higher recession speeds—which would mean a more rapid expansion rate for the universe. The Interactive Figure (in red) shows a graph of the Cepheid period-luminosity relation. This graph indicates that __________. Cepheids with longer periods have higher luminosities A Cepheid with a period of 30 days has an average luminosity that is about __________ times the luminosity of the Sun. 10,000 What actually causes a Cepheid to vary in apparent brightness? The Cepheid varies in radius, and its luminosity is greater when its radius is larger. What is the approximate luminosity of the Cepheid whose light curve is shown in the graph? 8000 Lsun Radar, the first link in the cosmic distance chain, is used to establish the baseline distance necessary for the second link, parallax. What baseline distance must we know before we can measure parallax? the Earth-Sun distance What is the three-step processes that describes how we use Cepheids as a tool to make cosmic distance measurements? Step 1: Measure the period of the Cepheid's brightness variations. Step 2: Use the period-luminosity relation to determine the Cepheid's luminosity. Step 3: Calculate the Cepheid's distance from its luminosity and apparent brightness. Which cosmic distance measurement techniques are considered standard candle techniques? (1) Main-sequence fitting (2) White dwarf supernovae (distant standards) (3) Cepheids
Suppose that Cepheids did not exist and there were no other standard candle technique that worked at the same distances. What would be true? We would not be able to measure the distances of distant galaxies. Explanation: (2) White dwarf supernovae, in turn, allow us to calibrate Hubble's law. (3) Therefore, without Cepheids, we would not be able to use either white dwarf supernovae or Hubble's law, and we would be unable to measure the distances of distant galaxies. Why do we use Hubble's law to estimate the distances of most distant galaxies, rather than using white dwarf supernovae in all cases? We have not observed white dwarf supernovae in most galaxies. Imagine that radar had never been invented and that we instead had to rely on a less reliable method of measuring distances in our solar system. If that method led us to underestimate the Earth-Sun distance by 10%, how would it affect other measurements in the distance chain? They would all be off by the same 10%. Which technique is the most useful for measuring the distance to a galaxy located 10 million light-years away? Cepheids Which distance measurement technique is most suited to measuring objects at a distance of 10 million light-years? Cepheids Which distance measurement technique is most suited to measuring objects at a distance of 10 light-years? parallax Which standard-candle technique is best for measuring the distances of very distant galaxies? distant standards What color(s) in the image represent(s) the radio emission? Purple and pinkish-white What is the approximate distance from the far edge of one lobe to the far edge of the other? approximately 2,100,000 light-years What is the approximate size of the visible galaxy producing the jets? about 200,000 light-years in diameter What are some distinguishing characteristics of Spiral galaxies? (1) have flattened disk of stars (2)contain many bright, hot stars (3) have significant, ongoing star formation (4) are rare in central regions of galaxy clusters (5) contain abundant clouds of cool gas and dust What are some distinguishing characteristics of Elliptical galaxies? (1) are more reddish in color (2) contain primarily old, low-mass stars 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. What creates an elliptical galaxy? (1) stars form rapidly as the protogalactic cloud shrinks (2) protogalactic cloud has high density (3) a galaxy collision strips away gas (4) protogalactic cloud rotates very slowly Processes that do not allow gas to settle into a disk (or that strip gas away) lead to elliptical galaxies. 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. (1) most protogalactic gas settles into a disk (2) protogalactic cloud has high angular momentum Processes that allow gas to settle into a disk lead to spiral galaxies Suppose a collision strips gas out of a spiral galaxy. Why would this tend to change the spiral galaxy into an elliptical galaxy? a galaxy cannot have a disk if it does not have gas 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? Rapid star formation means that there may not be enough gas left to make a disk. High angular momentum leads to faster rotation. Why does faster rotation tend to lead to a spiral galaxy, rather than an elliptical galaxy? 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. ___________ 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. starburst galaxies The largest individual galaxies in the universe are known as ________. central dominant galaxies The collective activity of many supernova events in a relatively small volume of a galaxy can create ________. galactic wind The most luminous objects in the universe are __________. quasars The energy for all active galactic nuclei is thought to comes from in-fall of matter into __________. supermassive black holes ___________ are often characterized by sources of immense energy located hundreds of thousands of light-years away on either side of their centers. radio galaxies Why do astronomers hypothesize that a massive black hole lies at the center of M87? A very small region at the center of M87 releases an enormous amount of energy. 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? 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. 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? Gravitational potential energy is converted to thermal energy as matter from the surrounding gas disk spirals into the central black hole. Which of these galaxies would you most likely find at the center of a large cluster of galaxies? a large elliptical galaxy We determine the distance of a Cepheid by ____________. determining its luminosity from the period-luminosity relation and then applying the inverse square law for light. Which kind of object is the best standard candle for measuring distances to extremely distant galaxies? a white dwarf supernovae Why do virtually all the galaxies in the universe appear to be moving away from our own? Because expansion causes all galaxies to move away from nearly all others. Which of these galaxies is most likely to be oldest? (1) a galaxy in the Local Group (2) a galaxy observed at a distance of 5 billion light-years (3) a galaxy observed at a distance of 10 billion light-years (1) a galaxy in the Local Group When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was __________. 4 billion (giga) years old Which of these items is a key assumption in our most successful models for galaxy formation? Some regions of the universe were slightly denser than others. Observations indicate that galaxies with more massive central black holes tend to also have _________________. a greater mass of stars in their central bulges The luminosity of a quasar is generated in a region the size of _________. the solar system The primary source of a quasar's energy is gravitational potential energy The globular cluster M13 belongs to the _____________ of the Milky Way Galaxy. halo component A(n) ___________ contains hot, ionized gas but very little cool gas or dust. elliptical galaxy The type of galaxy known as a(n) ___________ was more common in the universe 10 billion years ago. irregular galaxy The Milky Way is a(n) ________. spiral galaxy Our Sun belongs to the _______ of the Milky Way Galaxy. disk component Scientists investigating _________ study how the distribution of galaxies changes with time. cosmology What are the 3 major categories of galaxies? (1) Spiral galaxies (2) Elliptical galaxies (3) Irregular galaxies What is a standard candle? a light source of known luminosity What two observable properties of a Cepheid variable are directly related to one another? the period between its peaks of brightness and its luminosity What does Hubble's law tell us? The more distant a galaxy, the faster it is moving away from us. If we say that a galaxy has a lookback time of 1 billion years, we mean that _________. its light traveled through space for 1 billion years to reach us Current estimates place the age of the universe at about _________. 14 billion (giga) years What type of galaxy is M82 based on its appearance in the visible-light view? irregular Look again at the visible-light view of M82. What is the source of the white and blue light that dominates the image? stars 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? The red is emission from warm dust grains; the whitish-blue is emission from stars. What is seen in the images from the previous questions? Stars in the central region of this galaxy are exploding as supernovae, generating a galactic wind of hot gas and warm dust gains. What can we conclude about this galaxy from the fact that there are so many supernovae occurring? This galaxy contains an unusually large number of young stars. 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? At its current rate of star formation, the galaxy would use up all its dust and gas in just a few hundred million years. Telescopes designed to study the earliest stages in galactic lives should be optimized for observations in ______. infrared light 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 Why should galaxy collisions have been more common in the past than they are today? Galaxies were closer together in the past because the universe was smaller. Which of the following phenomena is probably NOT related to the presence of a supermassive black hole? the presence of globular clusters in the halos of galaxies According to the theory that active galactic nuclei are powered by supermassive black holes, the high luminosity of an active galactic nucleus primarily consists of ______. light emitted by hot gas in an accretion disk that swirls around the black hole What phenomena are related to the presence of a supermassive black hole? (1) quasars (2) the radio emission from radio galaxies (3) the huge jets seen emerging from the centers of some galaxies Students also viewedAssignment 20 - Galaxies & Cosmology18 terms Babynino_love AST1002 HW 629 terms mjmilner98 Astronomy Homework 11305 terms Baily_Manuppella2 Ch2016 terms Darrell_Creecy Sets found in the same folderASTR 101 Chapter 1751 terms linzi_standiford9 astr ch 6 & 1452 terms kimchix Chapter 18 Homework52 terms samarchi astronomy 1-3 hw141 terms kaelyndaniels Other sets by this creatorHospital Areas21 terms samarchi The Head21 terms samarchi Parts of the Hand10 terms samarchi The Foot9 terms samarchi Verified questionsphysics An object is between a convex lens and its focal point. Is the image real or virtual? Is it larger or smaller than the object? Explain. Verified answer
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Is the universe 13.8 billion years old?The universe is about 13.8 billion years old, according to new research published in a series of papers by an international team of astrophysicists, including Stony Brook's Neelima Sehgal.
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What is the estimated age of the universe quizlet?What is the best estimate for the age of the universe? 13.8 billion years old.
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Current estimates place the age of the universe at about _____.
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