Quiz 13

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

A)higher mass-to-light ratios because stars in elliptical galaxies are dimmer than those in spirals.

How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected? A)through observations of the 21 cm line of atomic hydrogen B)through observations of spectral lines of dark matter C)by measuring the broadening of absorption lines D)by watching the galaxies rotate over a period of years E)by extrapolation

A)through observations of the 21 cm line of atomic hydrogen

Which of the following is an example of baryonic matter? A)you B)WIMPs C)neutrinos D)electrons and positrons produced by pair production E)the particles produced by physicists in particle accelerators

A)you

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

B)It emits no or very little radiation of any wavelength.

What do we mean when we say that a particle is a weakly interacting particle? A)It is so small that it doesn't affect objects in the universe. B)It interacts only through the weak force and the force of gravity. C)It is the only type of particle that interacts through the weak force. D)It doesn't interact with any type of baryonic matter. E)It interacts only through the weak force.

B)It interacts only through the weak force and the force of gravity.

If there is no dark matter in the Milky Way Galaxy, what is the best alternative explanation for the observations? A)We are not attributing enough mass to the visible or "bright" matter. B)Our understanding of gravity is not correct for galaxy-size scales. C)We are not measuring the distances to atomic clouds and stars properly. D)We are not observing all the visible or "bright" matter in the galaxy. E)We are not measuring the orbital velocities of atomic clouds and stars properly.

B)Our understanding of gravity is not correct for galaxy-size scales.

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

B)White-dwarf supernovae are slightly dimmer than expected for a coasting universe.

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

B)massive objects bend light beams that are passing nearby.

Which of the following particles are baryons? A)quarks B)protons C)neutrinos D)photons E)electrons

B)protons

When we see that a spectral line of a galaxy is broadened, that is, spanning a range of wavelengths, we conclude that A)we are actually measuring the orbital velocity of dark matter. B)there are different Doppler shifts among the individual stars in the galaxy. C)we are actually measuring the orbital velocity of a cloud of atomic gas. D)there are many stars traveling at extremely high orbital velocities. E)we do not have very good resolution of a star's orbital velocity.

B)there are different Doppler shifts among the individual stars in the galaxy.

If a galaxy's overall mass-to-light ratio is 100 solar masses per solar luminosity, and its stars account for only 5 solar masses per solar luminosity, how much of the galaxy's mass must be dark matter? A)50 percent B)5 percent C)95 percent D)100 percent E)80 percent

C)95 percent

Why do we believe 90 percent of the mass of the Milky Way is in the form of dark matter? A)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. B)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. C)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. D)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.

D)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.

What might be causing the universe to accelerate? A)white-dwarf supernovae B)WIMPs C)dark gravity D)We don't know!-but we call it "dark energy." E)neutrinos

D)We don't know!-but we call it "dark energy."

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

D)the agent causing the universal expansion to accelerate

What is the ultimate fate of an open universe? A)Individual stars die but their gas is recycled through the interstellar medium and new stars form in a never-ending process. B)Stars will expand away from each other and galaxies effectively "evaporate." C)All matter eventually ends up in massive black holes. D)the Big Crunch E)All matter decays to a low-density sea of photons and subatomic particles.

E)All matter decays to a low-density sea of photons and subatomic particles.

What does the universe look like on very large scales? A)Galaxies are distributed in a hierarchy of clusters, superclusters, and hyperclusters. B)Galaxies are uniformly distributed. C)Galaxies are distributed in a great shell expanding outward from the center of the universe. D)Galaxies are randomly distributed. E)Galaxies appear to be distributed in chains and sheets that surround great voids.

E)Galaxies appear to be distributed in chains and sheets that surround great voids.

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

E)approximately spherical and about ten times the size of the galaxy halo.

Measuring the amount of deuterium in the universe allows us to set a limit on A)the total amount of mass in the universe. B)the temperature of the universe at the end of the era of nuclei. C)the expansion rate of the universe. D)the current age of the universe. E)the density of ordinary (baryonic) matter in the universe.

E)the density of ordinary (baryonic) matter in the universe.