ASTR 101 Final – HW 10 – Flashcards

When a proton and an antiproton collide, they A. repel each other. B. fuse together. C. convert into two photons.

Which statement about the cosmic microwave background is NOT true? A. With the exception of very small variations, it appears essentially the same in all directions in which we look into space. B. It is thought to be radiation that began its journey to our telescopes when the universe was about 380,000 years old. C. It is the result of a mixture of radiation from many independent sources, such as stars and galaxies. D. Its spectrum corresponds to a temperature of just under 3 degrees above absolute zero.

Patterns in the cosmic microwave background tell us about conditions in the early universe that ultimately led to galaxy formation. A. This statement makes sense. Cosmic microwave background is a primary source of information about what the universe was like at an age of about 380,000 years. The detailed observations of small temperature variations of the microwave background are very important to studies of galaxy evolution, because all large structures in the universe are thought to have formed around the regions of slightly enhanced density at early age of of the universe. B. This statement doesn't make sense. The cosmic microwave background did not really come from the heat of the universe itself but instead came from many individual stars and galaxies. Therefore it is not useful in study of the early universe.

The current temperature of the universe as a whole is A. absolute zero. B. a few K. C. a few thousand K.

Which of the following does not provide strong evidence for the Big Bang theory? A. observations of the cosmic microwave background B. observations of the amount of hydrogen in the universe C. observations of the ratio of helium to hydrogen in the universe

When the universe was 380,000 years old, its thermal radiation spectrum consisted mostly of A. radio and microwave photons. B. visible and infrared photons. C. X-ray and ultraviolet photons.

According to the hypothesis of inflation, the "flat" geometry of the universe most likely arose by chance. A. This statement makes sense. Einstein's general theory of relativity tells us that matter and energy produce curvature of spacetime. The observations have detected that the overall geometry of the universe has a significant curvature that depends on the expansion rate of different regions of universe and the overall amount of matter and energy the regions contain. B. This statement doesn't make sense. As far as we can tell, the large-scale geometry of the universe is flat, meaning that the effects of matter and energy on the overall curvature precisely balance the effects of the expansion rate.

Which of the following does inflation help to explain? A. the uniformity of the cosmic microwave background B. the amount of helium in the universe C. the temperature of the cosmic microwave background

Which of these pieces of evidence supports the idea that inflation really happened? A. the enormous size of the observable universe B. the large amount of dark matter that the universe contains C. observations of the cosmic microwave background that indicate a flat geometry for the universe

What is the earliest time in the universe that we can directly observe? A. a few hundred million years after the Big Bang B. a few hundred thousand years after the Big Bang C. a few minutes after the Big Bang

Which of these options is the best explanation for why the night sky is dark? A. The universe is not infinite in space. B. The universe has not always looked the way it looks today. C. The distribution of matter in the universe is not uniform on very large scales.

How do we determine the conditions that existed in the very early universe? A. We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size. B. We look all the way to the cosmological horizon, where we can see the actual conditions that prevailed all the way back to the first instant of the Big Bang. C. We can only guess at the conditions, since we have no way to calculate or observe what they were. D. The conditions in the very early universe must have been much like those found in stars today, so we learn about them by studying stars.

Why can't current theories describe what happened during the Planck era? A. The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant. B. We do not know how hot or dense the universe was during that time. C. We do not understand the properties of antimatter. D. We do not yet have a theory that links quantum mechanics and general relativity.

What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old? A. It marks the time at which the expansion of the universe had settled down to its current rate. B. It marks the time at which the first stars formed. C. The basic chemical composition of the universe had been determined. D. The proportions of dark matter and luminous matter had been determined.

In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why? A. 380,000 years after the Big Bang marks the time when stars were first born, and thus began to shine the light by which we can see the universe. B. Before that time, the universe was too crowded with stars. C. Before that time, the universe was dark so there was no light to illuminate anything. D. Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely.

If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for ________. A. the relationship between the strong and the weak force B. the fact that our universe is expanding C. how galaxies came to exist D. the existence of helium in the universe

In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe? A. Helium fusion occurred, but the carbon nuclei that were made were later destroyed by the intense radiation in the early universe. B. Temperatures in the early universe were never above the roughly 100 million Kelvin required for helium fusion. C. By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur. D. No one knows-this is one of the major mysteries in astronomy.

The Big Bang theory seems to explain how elements were formed during the first few minutes after the Big Bang. Which hypothetical observation below (these are not real observations) would call our current theory into question? A. the discovery of a star-like object made entirely of carbon and oxygen B. the discovery of a galaxy with 27% helium rather than the 25% that theory tells us was produced in the Big Bang C. the discovery of a planet that with no helium in its atmosphere D. the discovery of a galaxy with a helium abundance of only 10% by mass

The four fundamental forces that operate in the universe today are ________. A. strong force, weak force, electromagnetic force, gravity B. strong force, weak force, electric force, magnetic force C. nuclear force, gravity, electric force, magnetic force D. nuclear force, electromagnetic force, gravity, tidal force

What do we mean by inflation? A. a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe's first second of existence B. the expansion of the universe that we still observe today C. the sudden release of photons when a particle and antiparticle annihilate one another D. quantum fluctuations by high speed, relativistic particles in a state of false vacuum that caused disturbances in the space-time continuum leading to the process described in the question to which this answer refers

Why did the era of nucleosynthesis end? A. Too many heavy elements were produced. B. Neutrinos carried off too much energy. C. The temperature of the universe became too low. D. The density of the universe became too low.

What is postulated to have caused a sudden inflation of the early universe? A. the energy absorbed by the separation of the electromagnetic and weak forces B. the energy released from the "freezing out" of the strong force from the GUT force C. the energy absorbed by giant quantum fluctuations D. the energy released from the annihilation of matter and antimatter E. the energy released in the fusion of protons and neutrons to produce helium

Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the simple question posed by Olbers' paradox? A. How many stars are in the universe? B. Why is the sky dark at night? C. Can we measure the position and momentum of an electron at the same time? D. How does the Sun produce energy? E. What would it be like to ride on a beam of light?

T/F: Galaxies formed from tiny density perturbations that formed prior to the inflationary period.

Which of the following claims cannot be proved or disproved by science? A. The universe is about 14 billion years old. B. The universe is about 2000 years old. C. The universe started out very hot. D. The universe was created by God.

Which event in the history of the universe happened last? A. The GUT force separated into the electroweak force and strong force. B. Stable helium nuclei formed. C. The electroweak force separated into electromagnetic and weak nuclear forces. D. Neutral atoms formed.

The cosmic microwave background gives us a view of the universe when it was A. about 1 million years old. B. 3-5 minutes old. C. 380,000 years old. D. 14 billion years old.

How does the theory of inflation explain the near-uniformity of the cosmic microwave background? A. Matter was near the critical-density for a universal collapse, which smoothed out the differences in temperatures. B. The expanding universe would have cooled. C. Prior to rapid inflation, all regions of space were close enough to bounce radiation back-and-forth and reach the same temperature. D. Matter expanded into regions of space that had no matter, and thus ended up at the same temperature.

Which of the following best summarizes what we mean by dark energy? A. It is a name given to whatever is causing the expansion of the universe to accelerate with time. B. It is the energy contained in dark matter. C. It is a type of energy that is associated with the "dark side" of the force that rules the cosmos. D. It is the energy of black holes.

Which of the following best summarizes what we mean by dark matter? A. matter that may inhabit dark areas of the cosmos where we see nothing at all B. matter consisting of black holes C. matter for which we have theoretical reason to think it exists, but no observational evidence for its existence D. matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light

Dark energy has been hypothesized to exist in order to explain: A. observations suggesting that the expansion of the universe is accelerating. B. the high orbital speeds of stars far from the center of our galaxy. C. the giant voids between large-scale structures in the universe.

Dark matter is inferred to exist because: A. we see lots of dark patches in the sky. B. it explains how the expansion of the universe can be accelerating. C. we can observe its gravitational influence on visible matter.

Which of the following is NOT one of the three main strategies used to measure the mass of galaxy clusters? A. observing how the cluster bends light from galaxies located behind it B. measuring the temperatures of stars in the halos of the galaxies C. studying X-ray emission from hot gas inside the cluster D. measuring the speeds of galaxies orbiting the cluster's center

Which of the following statements best summarizes current evidence concerning dark matter in individual galaxies and in clusters of galaxies? A. Dark matter is present between galaxies in clusters, but not within individual galaxies. B. Within individual galaxies, dark matter is always concentrated near the galactic center, and within clusters it is always concentrated near the cluster center. C. Dark matter is the dominant form of mass in both clusters and in individual galaxies. D. Dark matter is present in individual galaxies, but there is no evidence that it can exist between the galaxies in a cluster.

Which of the following best sums up current scientific thinking about the nature of dark matter? A. About 90 percent of dark matter consists of ordinary matter in the halo of the galaxy, and the other 10 percent of WIMPs. B. Most dark matter probably consists of weakly interacting particles of a type that we have not yet identified. C. Dark matter probably does not really exist, and rather indicates a fundamental problem in our understanding of gravity. D. There is no longer any doubt that dark matter is made mostly of WIMPs.

Measurements of how orbital speeds depend on distance from the center of our galaxy tell us that stars in the outskirts of the galaxy A. rotate rapidly on their axes. B. travel in straight, flat lines rather than elliptical orbits. C. orbit the galactic center just as fast as stars closer to the center.

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: A. dark energy. B. spiral density waves. C. a gravitational lens.

Based on the observational evidence, is it possible that dark matter doesn't really exist? A. No, there is too much evidence to think that it could be in error. B. Yes, but only if there is something wrong with our current understanding of how gravity should work on large scales. C. Yes, but only if all the observations themselves are in error.

Based on current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies? A. subatomic particles that we have not yet detected B. swarms of dim, red stars C. supermassive black holes

Which region of the early universe was most likely to become a galaxy? A. a region whose matter density was lower than average B. a region whose matter density was higher than average C. a region with a high concentration of dark energy

What is the primary form of evidence that has led astronomers to conclude that the expansion of the universe is accelerating? A. observations of the speeds of individual galaxies in clusters B. measurements of how galaxy speeds away from the Milky Way have increased during the past century C. observations of white dwarf supernovae D. measurements of the rotation curve for the universe

Which of the following best sums up current scientific thinking about the nature of dark energy? A. Dark energy is the source of the mind weapon used by Sith Lords in Star Wars. B. Dark energy most likely consists of a form of photons that we can't see or detect. C. Dark energy is most likely made up of weakly interacting particles that do not interact with light. D. Dark energy probably exists, but we have little (if any) idea what it is.

Based on current evidence, what is the overall inventory of the mass-energy content of the universe? A. Current studies indicate that the actual density of the universe is about 32% of the critical density: 5% dark matter, 27% ordinary matter, including 0.5% from stars; that dark energy represents about 68% of the critical density. B. Current studies indicate that the actual density of the universe is about 32% of the critical density: 27% dark matter, 5% ordinary matter, including 0.5% from stars; that dark energy represents about 68% of the critical density. C. Current studies indicate that the actual density of the universe is about 73% of the critical density: 68% dark matter, 5% ordinary matter, including 0.5% from stars; that dark energy represents about 27% of the critical density. D. Current studies indicate that the actual density of the universe is about 73% of the critical density: 5% dark matter, 68% ordinary matter, including 0.5% from stars; that dark energy represents about 27% of the critical density.

What implications does the evidence for dark energy have for the fate of the universe? A. The expansion would continually slow down with time and eventually would stop entirely and then reverse. Galaxies would come crashing back together. B. The galaxies would always move apart at approximately the speeds they have today. C. The expansion would decelerate forever, leading to a universe that would never collapse but would expand ever more slowly as time progressed. D. The expansion would accelerate with time, causing galaxies to recede from one another with ever-increasing speed.

Why do we call dark matter "dark"? A. It blocks out the light of stars in a galaxy. B. It emits no visible light. C. It emits no or very little radiation of any wavelength. D. We cannot detect the type of radiation that it emits.

The distribution of the dark matter in a spiral galaxy is A. flattened in a disk but about ten times larger than the stellar disk. B. flattened in a disk and about the same size as the stellar disk. C. predominantly concentrated in the spiral arms. D. approximately spherical and about the same size as the galaxy halo. E. approximately spherical and about ten times the size of the galaxy halo.

A gravitational lens occurs when A. a massive object causes more distant objects to appear much larger than they should, and we can observe the distant objects with better resolution. B. dark matter builds up in a particular region of space, leading to a very dense region and an extremely high mass-to-light ratio. C. a massive object bends light beams that are passing nearby. D. a telescope lens is distorted by gravity.

The gravitational lens effect has been verified by A. single images of highly distorted, high-redshift galaxies seen towards massive galaxy clusters. B. observations of the bending of starlight by the Sun during a 1919 eclipse. C. observations of multiple images of the same background galaxy seen towards a massive galaxy cluster. D. all of the above E. None of the above; this effect is purely hypothetical.

Which of the following is not evidence for dark matter? A. the flat rotation curves of spiral galaxies B. the expansion of the universe C. the broad absorption lines found in the spectra of elliptical galaxies D. X-ray observations of hot gas in galaxy clusters E. gravitational lensing around galaxy clusters

This figure shows the X-ray emission from hot gas in two colliding galaxy clusters (red) and the distribution of mass (blue). Which of these are reasonable conclusions that can be drawn from this image? I) The mass found by gravitational lensing in these colliding galaxy clusters is in a separate physical location from the hot gas that resulted from the collision. II) Dark matter does not physically interact with regular matter, other than through gravity. III) Hot intracluster gas makes up the majority of the mass of galactic clusters.

Which of the following are candidates for galactic dark matter? A. brown dwarfs B. Jupiter-size objects C. faint red stars D. WIMPs E. all of the above

What do we mean when we say that a particle is weakly interacting? A. It doesn't interact with any type of baryonic matter. B. It interacts with other particles only through the weak force. C. It interacts only with other weak particles, such as neutrinos. D. It interacts with other particles only through the weak force and the force of gravity. E. It interacts with other particles only through the weakest force, gravity.

Why isn't the space within our solar system or the Milky Way expanding according to Hubble's Law? A. The gravity exerted by the solar system and the Milky Way is strong enough to hold them together against the expansion of the universe. B. The universe is not old enough for the solar system or Milky Way to have begun their expansion. C. Hubble's law of expansion applies only to the space between galaxies. D. As we are inside our solar system and the Milky Way, we cannot observe their expansion.

Which of the following best describes how galaxies are distributed on large scales in the universe? A. Galaxies are distributed in a great shell expanding outward from the center of the universe. B. Galaxies are randomly distributed. C. Galaxies appear to be distributed in chains and sheets that surround great voids. D. Galaxies are distributed in a hierarchy of clusters, superclusters, and hyperclusters. E. Galaxies are uniformly distributed.

How have astronomers measured the acceleration of the universe? A. by measuring changes in galaxies' redshifts from year to year B. by comparing lookback times for white-dwarf supernovae (by measuring their apparent brightness) with the average distance between galaxies (based on their cosmological redshifts) C. They have not. It is a purely hypothetical idea.

Why is the cause of the acceleration of the universe called "dark energy"? A. Dark energy and dark matter are just two forms of the same thing. B. We're pretty sure that whatever is causing the acceleration is pure evil. C. The term dark energy was the one that caught on with other astronomers.

Which of the following would not be considered evidence for dark matter in clusters of galaxies? A. the curvature of gravitationally-lensed galaxies B. the temperature of the intergalactic gas C. the velocities and radii of galaxy orbits around the center of mass in the cluster D. the total amount of stars

What is one of the alternatives to the hypothesized existence of dark matter? A. The theory of gravity is wrong. B. The astronomers are misrepresenting the observations. C. The observations are incorrect. D. The current theory of gravity is being used incorrectly.

Consider the data points together with the models in the graph of expansion models. Which model is most strongly supported by the data? A.recollapsing B. coasting C. critical D.accelerating

Comparing the following 4 models, which model predicts that galaxies had the largest separations in the past? (Use the graph of expansion models as a guide.) A.accelerating B. coasting C. critical D.recollapsing

Consider the graph of expansion models. Which model(s) predicts that galaxies will eventually get closer together? A.accelerating B. coasting C. critical D.recollapsing E. all of them F. none of them

The graph above shows 4 models for how the average distance between galaxies could change with time, from the past (left) to now (middle ) to the future (right hand side ). The graph also shows real data, based on studies of supernovae. Each black dot on the graph is for one supernova explosion. The data are plotted with dots and black lines that indicate the range of uncertainty of each individual measurement. Use this graph to answer the following question about cosmological models for the expansion of the universe. (Note that the models are in the same order, from top to bottom, whether on the right hand side of the graph or the left hand side. For example the accelerating model is the top line on both sides of the graph. You should also have a handout with a better version of this graph.) Which model(s) predict that galaxies are getting farther apart NOW? A.accelerating B. coasting C. critical D.recollapsing E. all of them F. none of them

What might be causing the universe to accelerate? A. dark energy B. gravitation C. WIMPs D. white-dwarf supernovae E. brown dwarfs