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1. What is the diameter of the disk of the Milky Way?
What is the diameter of the disk of the Milky Way?100 light years1,000 light years10,000 light years100,000 light years1,000,000 light yearsWhat kinds of objects lie in the halo of our galaxy?open clustersO and B starsglobular clustersgas and dustall of the aboveWhat makes up the interstellar medium?open clustersO and B starsK and M starsgas and dustall of the aboveWhich of the following comprise the oldest members of the Milky Way?the Sun and other solar mass starsO starsred giant stars in spiral armsCepheid variablesglobular clustersWhere are most heavy elements made?in the interstellar mediumin stars and supernovaein the Big Bang, when the universe first begannone of the aboveall of the aboveWhich of the following statements about the spiral structure of spiral galaxies is false?Hot blue stars are mostly found there.It is believed that the spiral shape is maintained by density-wave propagation in the disk as the result of galactic interactions.Supernovae occur near spiral armsOver a short period of time, spiral arms wind around on themselves more and more tightly.What produces the 21-cm line that we use to map out the Milky Way Galaxy?atomic hydrogenionized hydrogenmolecular hydrogencarbon monoxideheliumWhich of the following is true regarding the kinds of events we uncover looking at the Milky Way using different wavelengths of light?Infrared reveals areas around star formation.Radio waves reveal star-forming regions and the emission from CO from cold dark molecular clouds.The 21-cm line reveals atomic hydrogen.X-rays reveal locations of supernovae and hot bubbles of expanding gas.All the above is correct.Why do we believe 90 percent of the mass of the Milky Way is in the form of dark matter?The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material.Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk, suggesting that the halo is full of dark matter.Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are dark matter located in the halo.Where does most star formation occur in the Milky Way today?in the haloin the bulgein the spiral armsin the Galactic centeruniformly throughout the GalaxyWhat massive object is believed to lie at the center of the Milky Way?A stellar-mass black holeA supermassive black holeA superbubble of the expanding gases from thousands of supernovaePeanuts and caramel Chapter 20 Homework QuestionsBased on counting the number of galaxies in a small patch of the sky and multiplying by the number of such patches needed to cover the entire sky, the total number of galaxies in the observable universe is estimated to be approximately100 million.1 billion.10 billion.100 billion.1 trillion.Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?the one that is reddest in colorthe one that is bluest in colorthe one that is farthest awaythe one that is closest to usthe one that appears smallest in sizeWhich of the following is not a classification of galaxies?RadialSpiralEllipticalIrregularWhich of the following lists the hierarchy of structures from smallest to the largest in the correct order?stars, galaxies, large voids and filaments, groups and clusters, superclusterslarge voids and filaments, superclusters, groups and clusters, galaxies, starsstars, galaxies, groups and clusters, superclusters, large voids and filamentsstars, galaxies, superclusters, large voids and filaments, groups and clustersWhat is Hubble's law?The longer the time period between peaks in brightness, the greater the luminosity of the Cepheid variable star.The recession velocity of a galaxy is directly proportional to its distance from us.The recession velocity of a galaxy is inversely proportional to its distance from us.The faster a spiral galaxy's rotation speed, the more luminous it is.The faster a spiral galaxy's rotation speed, the less luminous it is.What is the Tully-Fisher relation?The longer the period of a galaxy's variable stars, the more luminous it is.The faster a spiral galaxy's rotation speed, the more luminous it is.The smaller a galaxy appears, the further away it is.The redder a galaxy's color, the further away it is.The further away a galaxy is, the faster its recession velocity.Which of the following is false about the expansion of the universe?Space is expanding, carrying the galaxies along with it.Wavelengths of light are lengthened as the light travels through space.Stars and galaxies are getting larger as the result of this expansion.The expansion rate can be measured by measuring the redshifts of distant galaxies.The Hubble constant is a measure of the expansion rate.Based on the Hubble constant, the age of the universe is about 14 billion years. Which of the following would result if the slope defining the Hubble constant were less?The calculated age of the universe would be less.The calculated age of the universe would be greater.The calculated age of the universe would remain unchanged.The calculated age of the universe would go infinite.All the equations would break down and no conclusion could be made.Why can't we see past the cosmological horizon?The universe extends only to this horizon.Beyond the cosmological horizon, we are looking back to a time before the universe had formed.We do not have telescopes big enough.We do not have sensitive enough detectors.The cosmological horizon is infinitely far away, and we can't see to infinity.Which of the following statements about the large-scale structure of the universe is false?Patterns of chains of galaxies and void spaces, on the largest scales, are isotropic and homogeneous.On the largest scales, matter is arranged in chains of galaxies with large void spaces.The process by which gravity forms the large-scale structure is well understood.Dark matter played a major role in helping to shape the large-scale structure.All the above is true.If a galaxy has a redshift of 33,000 km/sec and H0 is set to 70 km/sec/Mpc, then what it that galaxy's distance?2,300,000 Mpc471 Mpc2,300,000 pc471 pcNot enough information to tellChapter 21 Homework QuestionsHow do observations of distant galaxies help us learn about galaxy evolution?Observations at different distances show galaxies of different ages and therefore different stages of evolution.We can observe the birth of galaxies.We can observe the evolution of a single galaxy over time.We can observe two galaxies merging and what the result is, helping us learn how mergers affect evolution.We can see what our galaxy used to look like and therefore theorize about the physical processes that led to its current appearance.Why are telescopes sometimes called "time machines"?because the author, H.G. Wells, used the term to describe telescopes in a bookbecause some of the oldest telescopes are still in use todaybecause observations of distant objects reveal them as they were in the pastbecause astronomers can use telescopes to see the Milky Way as it was when it was much youngerIt's a journalistic misnomer: you cannot travel into the past or the future.The fact that most quasars are seen at greater distances suggests thatlight coming from them has been slowed down by the presence of the supermassive black hole in the middle.they are what galaxies are slowly evolving into.they are likely an early stage of evolution of galaxies.spacetime was expanding more slowly in the past.Galaxy collisions shouldn't have been more common in the past than they are now.Which of the following is not true of quasars?Some quasars are more than a thousand times more luminous than the Milky Way.Quasars were more common in the past.Quasars are powered by the energy radiated by matter falling into a central black hole.Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.Some quasars can change their brightness every few hours.The connection between the supermassive black hole mass and both the stellar speeds in the outskirts of the host galaxies and the masses of the host galaxies suggest thatsupermassive black holes may have been present during the formation of the galaxy and may have played a vital role in galaxy formation.galaxies came from matter spewing out of a supermassive black hole.galaxies will slowly fall into the supermassive black holegalaxies receding from us with greater speeds will have larger supermassive black holes.Which of the following is evidence for supermassive black holes in active galaxies?the discovery of powerful jets coming from a compact corerapid changes in the luminosity of the galaxy nucleusquasars emit approximately equal power at all wavelengths from infrared to gamma raysvery high speed orbital motions around galactic nucleiall of the aboveWhat is a recently suggested evolutionary track for galaxies from beginning to present?Condensation, supermassive black hole formation, quasar, active galaxy, normal galaxyCondensation, quasar, active galaxy, supermassive black hole formation, normal galaxySupermassive black hole formation, condensation, quasar, normal galaxySupermassive black hole formation, condensation, quasar, active galaxy, normal galaxyQuasars found closer to usare often in host galaxies that appear to have been disrupted by possible collisions or interactions with other galaxies.may have fired up as the result of interactions that has thrown material towards the supermassive black hole, causing it to fire up again.are found at smaller redshifts that more distant onesAll the above is correct.Which of the following statements about irregular galaxies is false?They are found in greater numbers in the distant past.They probably merged, as collisions were more common in the distant past, to form larger galaxies.When they are seen nearby, they seem to be the result of collisions (train wrecks!)They appear to be early stages of galaxy evolutionAll galaxies, due to titanic collisions will become disrupted irregular galaxies. Chapter 22 Homework QuestionsCurrently, our theoretical understanding of the behavior of matter and energy is good enough to describe generally what was happening in the universe ________ after the beginning.1 million years300,000 years300 years3 minutes10-43 secondWhich of the following is false, according to our present understanding of the beginning?The temperature just after the beginning was extremely high.As the universe expands and cools, structures of increasing complexity can form.Spacetime itself may have been created in the beginning, expanding ever since.There is no unique location where one can point and say that the birth of the universe occurred.We can experimentally test our ideas about the early univer to about 10-43 seconds after the beginning.Which of the following is false about the forces of nature in the early universe?We believe that all the fundamental forces were united as a single force that is routinely tested in accelerator laboratories.GUT refers to the unification of the strong, weak and electromagnetic forces.As the universe cools, the forces "freeze" or separate out from the unifying force to become different forces.We can currently test the electroweak force in particle accelerator laboratories.The "freezing" or separation of forces are the result of what physicists call spontaneous symmetry-breaking.When we say that the electroweak and strong forces "freeze out" at 10-36 seconds after the big bang, we mean thatthese forces are important only at temperatures below the freezing point of water; the temperature that the universe reached at an age of about 1020 second."freezing out" was a term coined by particle physicists who think that the big bang theory is really cool.prior to this time the electroweak and strong forces maintained a single identity, but they possessed separate identities following this time.following this time neither the strong nor the electroweak force was ever important in the universe again.quantum fluctuations by high-speed, relativistic particles in a state of false vacuum cause disturbances in the spacetime continuum, leading to the process described in the question this answer refers to.Which forces have physicists shown to be the same force under conditions of very high temperature or energy, as confirmed by experiments in particle accelerators?gravity and the weak forcegravity and the strong forcethe strong and weak forcesthe strong and electromagnetic forcesthe electromagnetic and weak forcesWhat do we mean by inflation? The sudden tremendous expansion of the universe caused by a yet-to-be-determined field.The expansion of the universe that makes elementary particles, like protons, much bigger.The sudden release of photons when a particle and antiparticle annihilate each otherThe separation that occurs after two photons collide and create a particle and an antiparticleWhich of the following statements about the cosmic background radiation is not true?It has a temperature of about 3 degrees K above absolute zero.It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.It had a much higher temperature in the past.It was discovered by Penzias and Wilson in the early 1960s.It appears essentially the same in all directions (it is isotropic).Helium originates fromstellar nucleosynthesis only.the big bang only.mostly from stellar nucleosynthesis with a small contribution from the big bang.mostly from the big bang with a small contribution from stellar nucleosynthesis.radioactive decay of heavier elements only.The study of cosmology and the understanding of the very early universe is most intimately tied to what other branch of science?GeologyMeteorologySolar physicsParticle physics10. Which of the following is false about the Big Bang Theory?It is a history of the early universe.It was developed by running the clock, and expansion, backwards.It solves the problem of how the universe was ultimately created.It has observational support, including information gleaned from the cosmic microwave background.Alternative theories exist that involve the universe living on a d-brane that collides with another d-brane. Chapter 23 Homework QuestionsWhy do we call dark matter "dark"?It emits light of other wavelengths, but not at visible wavelengths.We cannot detect the type of radiation that it emits.It emits no or very little radiation of any wavelength and it doesn't reflect light.It blocks out the light of stars in a galaxy.What evidence suggests that the Milky Way contains dark matter?We observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational attraction from objects that we can see.We see many lanes of dark material blocking out the light of stars behind them along the band of the Milky Way.We see many dark voids between the stars in the halo of the Milky Way.When we observe in different wavelengths, such as infrared or radio, we see objects that don't appear in visible-light observations.When we look at the galactic center, we are able to observe a large black hole that is composed of dark matter.The distribution of the dark matter in a spiral galaxy isapproximately spherical and about the same size as the galaxy halo.approximately spherical and about ten times the size of the galaxy halo.flattened in a disk and about the same size as the stellar disk.flattened in a disk but about ten times larger than the stellar disk.predominantly concentrated in the spiral arms.How do we determine the amount of dark matter in elliptical galaxies?We measure the orbital velocities of star-forming gas clouds around the outer portions of the galaxy.We measure the speeds of stars at different radii from the galactic center and determine how much mass is interior to the orbit.We count the number of stars in the galaxy and determine its volume, so that we can calculate the galaxy's density.We search for dark lanes of dust and black holes within the galaxy.We measure how fast the galaxy rotates as a whole.Which of the following is not evidence for dark matter?the flat rotation curves of spiral galaxiesthe broadening of absorption lines in an elliptical galaxy's spectrumX-ray observations of hot gas in galaxy clustersgravitational lensing around galaxy clustersthe fact that the universe is expandingDark energymay be the missing piece that halts the cosmic expansion, causing it to re-collapseis driving the expansion of the universe at an accelerating rate.is known as a common form of energy created in particle accelerator laboratories.None of the above is correct.A universe that is more than critical density, that has a closed geometry willcontinue to expand forever, but will always be at the threshold of collapse.continue to expand forever at an accelerated rate.collapse at some time in the future.will settle into a static state where the expansion halts, but will not collapse.None of the above.Methods for detecting the composition of dark matterinvolve attempts to detect machos through their gravitational lensing of more-distant starlight.involve attempts at direct detection of wimps using cold germanium crystals.involve attempts at indirect detection of very high energy neutrinos created by annihilating wimps inside massive bodies like the Sun.show that only a very small percentage of dark matter, if any, can be attributed to machos.All the above are true.Based on recent findings, which of the following statements are false about the mass/energy budget of the universe?95% of the content of the universe is a complete mystery to us so far as what the nature of this stuff is.Stars, galaxies, gas and dust, particles comprise less than 5% of the mass/energy budget of the universe.Dark matter makes up about 23% of the mass/energy budget of the universe.Dark energy makes up about 73% of the mass/energy budget of the universe.All the above is correct.Which of the following is not an important reason for understanding dark matter and dark energy?Most of the universe is made of these two dark components.Dark matter has the greatest influence on the motions of stars in galaxies and galaxies in clustersDark energy may have the greatest influence on the fate of the universe.Learning what the nature of these components are may revolutionize our understanding of physics.Dark energy is currently working to expand our solar system, which may result in the end of
