NATS 1740 Assignment 20

Dark matter is inferred to exist because: 1. we see lots of dark patches in the sky. 2. it explains how the expansion of the universe can be accelerating. 3. we can observe its gravitational influence on visible matter.

Dark energy has been hypothesized to exist in order to explain: 1. observations suggesting that the expansion of the universe is accelerating. 2. the high orbital speeds of stars far from the center of our galaxy. 3. explosions that seem to create giant voids between galaxies.

The flat part of the Milky Way Galaxy's rotation curve tells us that stars in the outskirts of the galaxy: 1. orbit the galactic center just as fast as stars closer to the center. 2. rotate rapidly on their axes. 3. travel in straight, flat lines rather than elliptical orbits.

Which region of the early universe was most likely to become a galaxy? 1. a region whose matter density was lower than average 2. a region whose matter density was higher than average 3. a region with an unusual concentration of dark energy

Based on current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies? 1.subatomic particles that we have not yet detected in particle physics experiments 2. swarms of relatively dim, red stars 3. supermassive black holes

The major evidence for the idea that the expansion of the universe is accelerating comes from observations of: 1. white dwarf supernovae. 2. the orbital speeds of stars within galaxies. 3. the evolution of quasars.

Why do we call dark matter "dark"? 1. It blocks out the light of stars in a galaxy. 2. We cannot detect the type of radiation that it emits. 3. It emits no visible light. 4. It emits no or very little radiation of any wavelength.

What is meant by "dark energy"? 1. the energy associated with dark matter through E=mc2 2. any unknown force that opposes gravity 3. highly energetic particles that are believed to constitute dark matter 4. the total energy in the Universe after the Big Bang but before the first stars 5. the agent causing the universal expansion to accelerate

How do we know that there is much more mass in the halo of our galaxy than in the disk? 1. Although the question of mass in the halo was long mysterious, we now know it exists because we see so many brown dwarfs in the halo. 2. The recent discovery of photinos, combined with theoretical predictions, tells us that there must be a huge mass of photinos in the halo. 3. We don't know that there is more mass in the halo; it is only a guess based on theory. 4. Stars in the outskirts of the Milky Way orbit the galaxy at much higher speeds than we would expect if all the mass were concentrated in the disk. 5. There are so many globular clusters in the halo that their total mass is greater than the mass of stars in the disk.

The distribution of the dark matter in a spiral galaxy is 1. flattened in a disk and about the same size as the stellar disk. 2. flattened in a disk but about ten times larger than the stellar disk. 3. approximately spherical and about ten times the size of the galaxy halo. 4. predominantly concentrated in the spiral arms. 5. approximately spherical and about the same size as the galaxy halo.

How do we determine the amount of dark matter in elliptical galaxies? 1. We count the number of stars in the galaxy and determine its volume, so that we can calculate the galaxy's density. 2. We measure how fast the galaxy rotates as a whole. 3. We measure the speeds of stars at different radii from the galactic center and determine how much mass is interior to the orbit. 4. We search for dark lanes of dust and black holes within the galaxy. 5. We measure the orbital velocities of star-forming gas clouds around the outer portions of the galaxy.

Compared to the central regions of spiral galaxies, we expect elliptical galaxies to have 1. lower mass-to-light ratios because elliptical galaxies have less gas and dust than spirals. 2. lower mass-to-light ratios because stars in elliptical galaxies are dimmer than those in spirals. 3. higher mass-to-light ratios because stars in elliptical galaxies do not have high orbital velocities. 4. higher mass-to-light ratios because stars in elliptical galaxies are dimmer than those in spirals. 5. the same mass-to-light ratio because they are made of the same material, stars and dark matter.

Which of the following methods used to determine the mass of a cluster does not depend on Newton's laws of gravity? 1. measuring the amount of distortion caused by a gravitational lens 2. measuring the temperature of X-ray gas in the intracluster medium 3. measuring the orbital velocities of galaxies in a cluster 4. none of the above

Gravitational lensing occurs when 1. dark matter builds up in a particular region of space, leading to a very dense region and an extremely high mass-to-light ratio. 2. massive objects bend light beams that are passing nearby. 3. massive objects cause more distant objects to appear much larger than they should and we can observe the distant objects with better resolution. 4. telescope lenses are distorted by gravity.

Which of the following particles are baryons? 1. protons 2. electrons 3. quarks 4. neutrinos 5. photons

Which of the following are candidates for dark matter? 1. faint red stars 2. WIMPs 3. brown dwarfs 4. Jupiter-size objects 5. all of the above

Why isn't space expanding within systems such as our solar system or the Milky Way? 1. The universe is not old enough yet for these objects to begin their expansion. 2. Their gravity is strong enough to hold them together against the expansion of the universe. 3. Hubble's law of expansion applies only to the space between galaxies. 4. We are so close to these systems that we don't observe their expansion.

What are peculiar velocities? 1. velocities perpendicular to our line of sight 2. velocities directly along our line of sight 3. velocities of distant objects that are not caused by the expansion of the universe 4. velocities that we cannot explain by only the force of gravity 5. velocities caused by the expansion of the universe

How do astronomers create three-dimensional maps of the universe? 1. by using the position on the sky and the galaxy brightness as a measure of distance along the line of sight 2. by interpreting the peculiar velocities of each galaxy 3. by carefully measuring the parallax of each galaxy 4. through comparison of computer models of the structure formation with observations 5. by using the position on the sky and the redshift to determine a distance along the line of sight

What does the universe look like on very large scales? 1. Galaxies are randomly distributed. 2. Galaxies are uniformly distributed. 3. Galaxies appear to be distributed in chains and sheets that surround great voids. 4. Galaxies are distributed in a great shell expanding outward from the center of the universe. 5. Galaxies are distributed in a hierarchy of clusters, superclusters, and hyperclusters.

Based on inventoried matter in the universe, including dark matter known to exist in galaxies and clusters, the actual density of the universe is what fraction of the critical density? 1. 100 percent 2. 200 percent 3. 25 percent 4. 1 percent 5. 10 percent

If all the "dark matter" in the Universe were to be, somehow, instantaneously removed, which of the following would not happen? 1. Clusters of galaxies would fly apart. 2. The Solar System would fly apart. 3. The Universe would expand forever. 4. The Milky Way would fly apart. 5. all of the above

Recent measurements of the expansion rate of the universe reveal that the expansion rate of the universe is doing something astronomers did not expect. What is that? 1. The measurements show that the universe may not be expanding at all. 2. The data show that the expansion rate varies widely in different parts of the universe. 3. The measurements indicate that the universe is at least 30 billion years old, meaning that more than 10 billion years passed between the Big Bang and the formation of the first stars and galaxies. 4. The measurements show that the universe may be shrinking rather than expanding. 5. The measurements show that the expansion is accelerating, rather than slowing under the influence of gravity.

What might be causing the universe to accelerate? 1. MACHOs 2. white-dwarf supernovae 3. dark gravity 4. WIMPs 5. We don't know! - but we call it "dark energy."

What is the evidence for an accelerating universe? 1. There is far more dark matter than visible matter in the universe. 2. White-dwarf supernovae are slightly dimmer than expected for a coasting universe. 3. The Andromeda Galaxy is moving away from the Milky Way at an ever-increasing speed. 4. White-dwarf supernovae are the same brightness regardless of redshift. 5. White-dwarf supernovae are slightly brighter than expected for a coasting universe.

Classify the given types of matter as either baryonic (meaning ordinary matter that contains protons and neutrons) or as nonbaryonic (meaning "extraordinary" matter that consists of more exotic subatomic particles). - matter in brown dwarfs - dark matter consisting of Jupiter-size objects in galactic halos - matter that probably makes up the majority of dark matter - matter in our bodies - matter in stars - dark matter consisting of weakly interacting subatomic particles

Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once. Sentences 1. An object the size of Earth located in the halo of our galaxy would be an example of the form of dark matter known as ___. 2. ___ are defined as subatomic particles that have more mass than neutrinos but do not interact with light. 3. Matter made from ordinary atoms represents what we call ___. 4. A massive object can distort the light of more distant objects behind it through the phenomenon that we call ___.5 5. The ___ of spiral galaxies provide strong evidence for the existence of dark matter. 6. Models show that the ___ of the universe is better-explained when we include the effects of dark matter along with the effects of luminous matter. Words a. WIMPS b. large-scale structure c. MACHOS d. rotation curvers e. baryonic matter f. gravitational lensing