Multiple Choice Questions

Which statement describes the trend among the galaxies shown on this graph?
  • It describes the expansion rate of the universe, with higher values meaning more rapid expansion.
  • Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull.
  • very high speed orbital motions around galactic nucleirapid changes in the luminosity of the galaxy nucleusquasars emit approximately equal power at all wavelengths from infrared to gamma raysthe discovery of powerful jets coming from a compact core
  • More distant galaxies tend to have a larger infrared color ratio, but there are some exceptions.
You discover a new cluster of galaxies, and the brightest galaxy in this new cluster has an infrared color ratio of 0.Based on the data in the graph, what is the approximate distance to this new cluster?
  • X-ray Emission from hot gas
  • 5 billion years, 2 billion light years, 800 million light years, 230 million light years, 70 million light years.
  • 1 Billion light years
  • 1.4 billion years
Suppose a collision strips gas out of a spiral galaxy. Why would this tend to change the spiral galaxy into an elliptical galaxy?
  • mapping the distribution of globular clusters in the galaxy.
  • A galaxy cannot have a disk if it does not have gas.
  • Active galactic nuclei tend to become less active as they age.
  • observations of gravitational lensing by the cluster
What do we mean by the straightest possible path between two points on Earth's surface?
  • It interacts only through the weak force and the force of gravity.
  • Clouds of gas are being heated by ultraviolet light from nearby, recently formed stars.
  • It is the idea that time runs slower in places where gravity is stronger.
  • the shortest path between the two points
Based on current estimates of the value of Hubble's constant, how old is the universe?
  • between 12 and 16 billion years old
  • warm, rarefied clouds of atomic hydrogen
  • It interacts only through the weak force and the force of gravity.
  • has greater density
What is the most accurate way to determine the distance to a nearby star?
  • It absorbs visible, ultraviolet, and some infrared light.
  • 100,000 light years
  • There are no blue halo stars.
  • stellar parallax ---- 1/arcsecond= parsecs
What kinds of objects lie in the disk of our galaxy?
  • It interacts only through the weak force and the force of gravity.
  • Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull.
  • open clustersgas and dustold K and M starsO and B stars
  • It is the idea that time runs slower in places where gravity is stronger.
Einstein's general theory of relativity suggests that gravity is ______.
  • Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull.
  • caused by curvature of spacetime
  • open clustersgas and dustold K and M starsO and B stars
  • It absorbs visible, ultraviolet, and some infrared light.
Based on the association of star formation with spiral arms, we can conclude that the gas in spiral arms __________ than it does in regions between the arms.
  • the shortest path between the two points
  • has greater density
  • 1 Billion light years
  • Flat Geometry: sum of angles of a triangle is always 180∘circumference of a circle is exactly 2πrSpherical Geometry:sum of angles of a triangle is greater than 180.straightest possible path is a segment of a great circle.lines that are initially parallel eventually convergeSaddle-Shaped Geometry: sum of angles of a triangle is less than 180∘lines that are initially parallel eventually diverge
What makes up the interstellar medium?
  • gas and dust
  • Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
  • Gas and dust are abundant in the disk but not in the halo.Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits.Clusters of young stars are found only in the disk.Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red.
  • 1,000 light years
What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
  • Flat Geometry: sum of angles of a triangle is always 180∘circumference of a circle is exactly 2πrSpherical Geometry:sum of angles of a triangle is greater than 180.straightest possible path is a segment of a great circle.lines that are initially parallel eventually convergeSaddle-Shaped Geometry: sum of angles of a triangle is less than 180∘lines that are initially parallel eventually diverge
  • The existence of gravitational waves is predicted by Einstein's general theory of relativity. The first direct detection of gravitational waves came in 2015. Gravitational waves carry energy away from their sources of emission. Gravitational waves are predicted to travel through space at the speed of light.
  • 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.
  • the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies.observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies.observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy.observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
What is a "Standard Candle"?
  • It interacts only through the weak force and the force of gravity.
  • the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole
  • It is the idea that time runs slower in places where gravity is stronger.
  • An object for which we are likely to know the true luminosity
LIGO detects gravitational waves because the lengths of its arms change as gravitational waves pass by. About how much are these lengths expected to change when LIGO detects gravitational waves from the merger of two neutron stars or two black holes?
  • only from the instant when the two objects merge into one
  • by an amount smaller than the diameter of a proton
  • observations of gravitational lensing by the cluster
  • Supernova A is twice as far away as Supernova B.
Why do astronomers hypothesize that a massive black hole lies at the center of M87?
  • an object with the same mass as the Sun but only half as large in radius
  • A very small region at the center of M87 releases an enormous amount of energy.
  • It emits no or very little radiation of any wavelength.
  • Clouds of gas are being heated by ultraviolet light from nearby, recently formed stars.
Hubble's "constant" is constant in
  • globular clusters
  • False
  • Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use cepheids as "Standard Candles" for distant measurements
  • Space
How do we know that there is much more mass in the halo of our galaxy than in the disk?
  • Clouds of gas are being heated by ultraviolet light from nearby, recently formed stars.
  • 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.
  • There are no blue halo stars.
  • 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.
Dr. X believes that the Hubble constant is H0 = 55 km/s/Mpc. Dr. Y believes it is H0 = 80 km/s/Mpc. Which statement below automatically follows?
  • detecting the same changes at more than one location
  • Supernova A is twice as far away as Supernova B.
  • Dr. X believes that the universe is older than Dr. Y believes.
  • only from the instant when the two objects merge into one
What do we mean when we say that a particle is a weakly interacting particle?
  • It interacts only through the weak force and the force of gravity.
  • all elements besides hydrogen and helium
  • It absorbs visible, ultraviolet, and some infrared light.
  • an object with the same mass as the Sun but only half as large in radius
The disk component of a spiral galaxy includes which of the following parts?
  • Using Cepheid Variables
  • stellar parallax ---- 1/arcsecond= parsecs
  • Spiral Arms
  • a galaxy cluster
If two straight lines start out parallel but eventually cross, then they must be in a _______.
  • It interacts only through the weak force and the force of gravity.
  • through observations of the 21 cm line of atomic hydrogen
  • Spherical Geometry
  • 100,000 light years
What is spacetime?
  • It emits no or very little radiation of any wavelength.
  • the inseparable combination of space and time
  • the expansion of the universe
  • It interacts only through the weak force and the force of gravity.
Watch the video that comes up when you click the icon "Star formation in spiral arms" in the interactive figure. Which of the following best describes what spiral arms are?
  • Spiral arms are waves of higher density that move outward through a galaxy, triggering star formation as they pass.
  • X-ray Emission from hot gas
  • Gravitational potential energy is converted to thermal energy as matter from the surrounding gas disk spirals into the central black hole.
  • 5 billion years, 2 billion light years, 800 million light years, 230 million light years, 70 million light years.
The following figures give the approximate distances of five galaxies from Earth. Rank the galaxies based on the speed with which each should be moving away from Earth due to the expansion of the universe, from fastest to slowest.
  • Individual stars orbit around the center of the galaxy. Individual stars move in and out of spiral arms over time.
  • Spiral arms are waves of higher density that move outward through a galaxy, triggering star formation as they pass.
  • 5 billion years, 2 billion light years, 800 million light years, 230 million light years, 70 million light years.
  • Yes, by photographing the new cluster with better angular resolution to see whether its brightest galaxy has an unusually bright center.
Why are Cepheid variables important?
  • Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use cepheids as "Standard Candles" for distant measurements
  • Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull.
  • Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
  • in stars and supernovae
What is the diameter of the disk of the Milky Way?
  • globular clusters
  • 100,000 light years
  • redder and rounder.
  • stellar parallax ---- 1/arcsecond= parsecs
The data in the figure show how the orbital period of the two neutron stars changes with time. Based on these data, what can we conclude?
  • detecting the same changes at more than one location
  • Supernova A is twice as far away as Supernova B.
  • 130,000 km/s, 45,000 km/s, 18,730 km/s, 5264 km/s, 1557 km/s
  • shorter and the two neutron stars are moving closer together
There are also two large blue-colored regions in the composite image. These blue regions are labeled as "dark matter" based on __________.
  • White-dwarf supernovae occur only among young and extremely bright stars.
  • observations of gravitational lensing by the cluster
  • detecting the same changes at more than one location
  • shorter and the two neutron stars are moving closer together
Why can't we see past the cosmological horizon?
  • Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
  • It absorbs visible, ultraviolet, and some infrared light.
  • measuring the distances to many distant galaxies with a standard candle technique
  • It interacts only through the weak force and the force of gravity.
If we say that a galaxy has a look back time of 1 billion years, we mean that _________.
  • the distance of a galaxy and the speed at which it is moving away from us (1/H0)
  • an object with the same mass as the Sun but only half as large in radius
  • its light traveled through space for 1 billion years to reach us
  • through observations of the 21 cm line of atomic hydrogen
If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about
  • only from the instant when the two objects merge into one
  • 3 m.
  • False
  • the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies.observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies.observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy.observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
High angular momentum leads to faster rotation. Why does faster rotation tend to lead to a spiral galaxy, rather than an elliptical galaxy?
  • Gravitational potential energy is converted to thermal energy as matter from the surrounding gas disk spirals into the central black hole.
  • 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.
  • ionization nebulae, massive stars (spectral types O and B), dense, dusty gas clouds, young stars
  • 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.
How was Edwin Hubble able to use his discovery of a cepheid in Andromeda to prove that the "Spiral Nebulae" were actually entire galaxies?
  • across the diameter of the galactic haloacross the diameter of the galactic diskfrom the Sun to the center of the galaxyacross the diameter of the central bulgethrough the disk from top to bottom
  • More common in Spiral Arms: ionization nebulae, dense dusty gas clouds, star formation, young starsMore common within and between Spiral Arms:Old Stars
  • From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
  • a globular cluster in the outskirts of the halo, a cloud of gas and dust in the outskirts of the diskour solar systemthe edge of the central bulge
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 __________.
  • shorter and the two neutron stars are moving closer together
  • It describes the expansion rate of the universe, with higher values meaning more rapid expansion.
  • measuring the distances to many distant galaxies with a standard candle technique
  • detecting the same changes at more than one location
Compared to spiral galaxies, elliptical galaxies are
  • redder and rounder.
  • globular clusters
  • the expansion of the universe
  • in stars and supernovae
The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?
  • A galaxy cannot have a disk if it does not have gas.
  • Active galactic nuclei tend to become less active as they age.
  • in the galactic disk, roughly halfway between the center and the outer edge of the disk
  • shorter and the two neutron stars are moving closer together
The Sun's location in the Milky Way Galaxy is _________.
  • an object with the same mass as the Sun but only half as large in radius
  • in the galactic disk, roughly halfway between the center and the outer edge of the disk
  • open clustersgas and dustold K and M starsO and B stars
  • shorter and the two neutron stars are moving closer together
What makes white-dwarf supernovae good standard candles?
  • gas and dust
  • They are very bright, so they can be used to determine the distances to galaxies billions of light-years away.They should all have approximately the same luminosity.
  • 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.
  • From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
We can in principle measure the expansion rate by studying galaxies in many different directions in space and at different times of year. If we compare such observations, we would find that the expansion rate is __________.
  • the same no matter when or in which direction we measure it
  • It emits no or very little radiation of any wavelength.
  • the shortest path between the two points
  • 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.
As noted in the Introduction, some scientists have proposed that dark matter does not really exist. According to this view, all matter is ordinary (baryonic), but at large distances from matter, gravity does not precisely obey either Newton's or Einstein's theories of gravity. Is this alternative view of gravity consistent with what we observe in the Bullet Cluster? Why or why not?
  • Elliptical Galaxies: stars form rapidly as the protogalactic cloud shrinks.protogalactic cloud has high density.A galaxy collision strips away gas.Protogalactic cloud rotates very slowly.Spiral Galaxies: most protogalactic gas settles into a disk.Protogalactic cloud has high angular momentum.
  • The Bullet cluster is actually two separate galaxy clusters that have collided, stripping out hot gas in the process.
  • No. If all matter was ordinary, then the blue region representing the location of most of the matter would line up with the red region representing the hot gas.
  • Individual stars orbit around the center of the galaxy. Individual stars move in and out of spiral arms over time.
Which of the following is evidence for supermassive black holes in active galaxies?
  • very high speed orbital motions around galactic nucleirapid changes in the luminosity of the galaxy nucleusquasars emit approximately equal power at all wavelengths from infrared to gamma raysthe discovery of powerful jets coming from a compact core
  • The Milky Way is much wider than it's thickness. So it is a narrow band with many stars in it, while the sky outside the band has much fewer stars.Shapley's 20th-century observations of globular cluster orbits, which center on a point about 30,000 light years from our Sun, showed we weren't in the center of the galaxy.
  • They all require rapid rotation , They are require very hot ionized gas,They all require hydrogen gas.
  • More distant galaxies tend to have a larger infrared color ratio, but there are some exceptions.
Sort each item into the appropriate bin according to whether it is more common in spiral arms or about equally common within and between the spiral arms in a spiral galaxy's disk.
  • No. If all matter was ordinary, then the blue region representing the location of most of the matter would line up with the red region representing the hot gas.
  • 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.
  • Supernova A is twice as far away as Supernova B.
  • More common in Spiral Arms: ionization nebulae, dense dusty gas clouds, star formation, young starsMore common within and between Spiral Arms:Old Stars
As predicted by general relativity, time runs slightly slower at the peak of Mount Everest than it does at sea level.
  • True
  • False
Consider the observation "The Andromeda Galaxy, a member of our Local Group, is moving toward us." Why doesn't this observation contradict the idea that the universe is expanding?
  • Rapid star formation means that there may not be enough gas left to make a disk.
  • Because the galaxies of the Local Group are gravitationally bound together.
  • across the diameter of the galactic haloacross the diameter of the galactic diskfrom the Sun to the center of the galaxyacross the diameter of the central bulgethrough the disk from top to bottom
  • It absorbs visible, ultraviolet, and some infrared light.
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?
  • Active galactic nuclei tend to become less active as they age.
  • The X-ray source is no more than a few light-days in diameter.
  • through observations of the 21 cm line of atomic hydrogen
  • A galaxy cannot have a disk if it does not have gas.
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.
  • a globular cluster in the outskirts of the halo, a cloud of gas and dust in the outskirts of the diskour solar systemthe edge of the central bulge
  • Gravitational potential energy is converted to thermal energy as matter from the surrounding gas disk spirals into the central black hole.
  • 5 billion years, 2 billion light years, 800 million light years, 230 million light years, 70 million light years.
Given such small length changes (as noted in Part D), what can give scientists confidence that they have really detected a gravitational wave signal?
  • It describes the expansion rate of the universe, with higher values meaning more rapid expansion.
  • A galaxy cannot have a disk if it does not have gas.
  • detecting the same changes at more than one location
  • Dr. X believes that the universe is older than Dr. Y believes.
A follow-up study showed that the galaxies that are exceptions to the general trend on the original graph have unusually brighter centers; that is, these galaxies contain active galactic nuclei. Based on this follow-up study, could you improve your confidence in your distance estimate for the new cluster discussed in Part B, and, if so, how?
  • Yes, by photographing the new cluster with better angular resolution to see whether its brightest galaxy has an unusually bright center.
  • Elliptical Galaxies: stars form rapidly as the protogalactic cloud shrinks.protogalactic cloud has high density.A galaxy collision strips away gas.Protogalactic cloud rotates very slowly.Spiral Galaxies: most protogalactic gas settles into a disk.Protogalactic cloud has high angular momentum.
  • 5 billion years, 2 billion light years, 800 million light years, 230 million light years, 70 million light years.
  • a globular cluster in the outskirts of the halo, a cloud of gas and dust in the outskirts of the diskour solar systemthe edge of the central bulge
What do we mean by gravitational time dilation?
  • all elements besides hydrogen and helium
  • It absorbs visible, ultraviolet, and some infrared light.
  • 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.
  • It is the idea that time runs slower in places where gravity is stronger.
The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on the amount of redshift that would be observed in each galaxy's spectrum, from largest to smallest.
  • 130,000 km/s, 45,000 km/s, 18,730 km/s, 5,264 km/s, 1,577 km/s
  • Dr. X believes that the universe is older than Dr. Y believes.
  • Yes, by photographing the new cluster with better angular resolution to see whether its brightest galaxy has an unusually bright center.
  • an object with the same mass as the Sun but only half as large in radius
Select the сorrect statements.
  • 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.
  • the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole
  • very high speed orbital motions around galactic nucleirapid changes in the luminosity of the galaxy nucleusquasars emit approximately equal power at all wavelengths from infrared to gamma raysthe discovery of powerful jets coming from a compact core
  • The Milky Way is much wider than it's thickness. So it is a narrow band with many stars in it, while the sky outside the band has much fewer stars.Shapley's 20th-century observations of globular cluster orbits, which center on a point about 30,000 light years from our Sun, showed we weren't in the center of the galaxy.
How are the masses of supermassive black holes related to the masses of the bulges of their surrounding galaxies and what does this suggest about the role of supermassive black holes in galaxy evolution.
  • Disk Stars: youngest starsThe sunstars that all orbit in nearly the same planehigh-mass starsHalo Stars:stars whose orbits can be inclined at any angle,stars with the smallest abundance of heavy elements,oldest stars,globular clusters
  • Galaxies with unusually bright nuclei are more common at greater distances.Galaxies with unusually bright nuclei were more common when the universe was young than they are today.On average, more distant galaxies have larger infrared color ratios.
  • very high speed orbital motions around galactic nucleirapid changes in the luminosity of the galaxy nucleusquasars emit approximately equal power at all wavelengths from infrared to gamma raysthe discovery of powerful jets coming from a compact core
  • Masses of supermassive black holes are proportional to the masses of the bulge components. The role of supermassive black holes in galaxy evolution is not clear, but somehow these black holes seem to grow along with the bulge component of their host.
What is a quasar?
  • A very small region at the center of M87 releases an enormous amount of energy.
  • They are very bright, so they can be used to determine the distances to galaxies billions of light-years away.They should all have approximately the same luminosity.
  • the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole
  • It interacts only through the weak force and the force of gravity.
Why do we call dark matter "dark"?
  • It emits no or very little radiation of any wavelength.
  • stellar parallax ---- 1/arcsecond= parsecs
  • It interacts only through the weak force and the force of gravity.
  • It absorbs visible, ultraviolet, and some infrared light.
With current technology, we expect to be able to detect (directly) gravitational waves from a binary system of two neutron stars or two black holes __________.
  • measuring the distances to many distant galaxies with a standard candle technique
  • only from the instant when the two objects merge into one
  • shorter and the two neutron stars are moving closer together
  • ionization nebulae, massive stars (spectral types O and B), dense, dusty gas clouds, young stars
the Bullet Cluster. What kind of cluster is it?
  • A galaxy cannot have a disk if it does not have gas.
  • a galaxy cluster
  • Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
  • Space
The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on their distance from Earth, from farthest to closest.
  • Active galactic nuclei tend to become less active as they age.
  • an object with the same mass as the Sun but only half as large in radius
  • shorter and the two neutron stars are moving closer together
  • 130,000 km/s, 45,000 km/s, 18,730 km/s, 5264 km/s, 1557 km/s
What is the thickness of the disk of the Milky Way?
  • Clouds of gas are being heated by ultraviolet light from nearby, recently formed stars.
  • You
  • 1,000 light years
  • redder and rounder.
The distribution of the dark matter in a spiral galaxy is
  • Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
  • More distant galaxies tend to have a larger infrared color ratio, but there are some exceptions.
  • approximately spherical and about ten times the size of the galaxy halo.
  • It is the idea that time runs slower in places where gravity is stronger.
A large mass-to-light ratio for a galaxy indicates that
  • on average, each solar mass of matter in the galaxy emits less light than our Sun.
  • It emits no or very little radiation of any wavelength.
  • Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull.
  • Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
The patterns on the graph of galaxy colors and luminosities allow scientists to make inferences about galaxy evolution. Which of the following statements accurately reflect current scientific thinking about galaxy evolution based on these data?
  • a globular cluster in the outskirts of the halo, a cloud of gas and dust in the outskirts of the diskour solar systemthe edge of the central bulge
  • Masses of supermassive black holes are proportional to the masses of the bulge components. The role of supermassive black holes in galaxy evolution is not clear, but somehow these black holes seem to grow along with the bulge component of their host.
  • All galaxies start their lives as members of the blue cloud.Very large galaxies tend to use up the gas available for star formation more rapidly than smaller galaxies.Some large red galaxies arose from mergers of smaller blue galaxies.
  • 5 billion years, 2 billion light years, 800 million light years, 230 million light years, 70 million light years.
How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected?
  • only from the instant when the two objects merge into one
  • It absorbs visible, ultraviolet, and some infrared light.
  • an object with the same mass as the Sun but only half as large in radius
  • through observations of the 21 cm line of atomic hydrogen
Based on what you have learned, which of the following best describes the meaning of Hubble's constant (H0 )?
  • Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull.
  • It interacts only through the weak force and the force of gravity.
  • between 12 and 16 billion years old
  • It describes the expansion rate of the universe, with higher values meaning more rapid expansion.
Recall that Hubble's law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0 = 65 km/s/Mpc. How fast would a galaxy located 500 megaparsecs distant be receding from us?
  • It should cause the orbits of the two objects to decay with time.
  • 32,500 km/s
  • the distance of a galaxy and the speed at which it is moving away from us (1/H0)
  • 1.4 billion years
Which of the following accurately describe some aspect of gravitational waves?
  • very high speed orbital motions around galactic nucleirapid changes in the luminosity of the galaxy nucleusquasars emit approximately equal power at all wavelengths from infrared to gamma raysthe discovery of powerful jets coming from a compact core
  • the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies.observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies.observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy.observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
  • The existence of gravitational waves is predicted by Einstein's general theory of relativity. The first direct detection of gravitational waves came in 2015. Gravitational waves carry energy away from their sources of emission. Gravitational waves are predicted to travel through space at the speed of light.
  • 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.
If you were to take a voyage across the Milky Way, what kind of material would you spend most of your time in?
  • the shortest path between the two points
  • The X-ray source is no more than a few light-days in diameter.
  • warm, rarefied clouds of atomic hydrogen
  • only from the instant when the two objects merge into one
Which of the following is not evidence for dark matter?
  • the expansion of the universe
  • in stars and supernovae
  • between 12 and 16 billion years old
  • very high speed orbital motions around galactic nucleirapid changes in the luminosity of the galaxy nucleusquasars emit approximately equal power at all wavelengths from infrared to gamma raysthe discovery of powerful jets coming from a compact core
What kinds of objects lie in the halo of our galaxy?
  • in stars and supernovae
  • 1,000 light years
  • There are no blue halo stars.
  • globular clusters
Massive-star supernovae and white-dwarf supernovae work equally well as standard candles for measuring cosmic distances.
  • True
  • False
White-dwarf supernovae are good standard candles for distance measurements for all the following reasons except which?
  • A very small region at the center of M87 releases an enormous amount of energy.
  • White-dwarf supernovae occur only among young and extremely bright stars.
  • It interacts only through the weak force and the force of gravity.
  • Active galactic nuclei tend to become less active as they age.
Click the icon "Spiral arm and star motion" in the interactive figure and watch the animation of the galaxy's rotation over several hundred million years. Which of the following statements accurately describe the motion?
  • across the diameter of the galactic haloacross the diameter of the galactic diskfrom the Sun to the center of the galaxyacross the diameter of the central bulgethrough the disk from top to bottom
  • No. If all matter was ordinary, then the blue region representing the location of most of the matter would line up with the red region representing the hot gas.
  • Individual stars orbit around the center of the galaxy. Individual stars move in and out of spiral arms over time.
  • They all require rapid rotation , They are require very hot ionized gas,They all require hydrogen gas.
Each item below belongs either with the population of disk stars or the population of halo stars of the Milky Way Galaxy. Match each item to the appropriate population.
  • ionization nebulae, massive stars (spectral types O and B), dense, dusty gas clouds, young stars
  • Disk Stars: youngest starsThe sunstars that all orbit in nearly the same planehigh-mass starsHalo Stars:stars whose orbits can be inclined at any angle,stars with the smallest abundance of heavy elements,oldest stars,globular clusters
  • The existence of gravitational waves is predicted by Einstein's general theory of relativity. The first direct detection of gravitational waves came in 2015. Gravitational waves carry energy away from their sources of emission. Gravitational waves are predicted to travel through space at the speed of light.
  • a globular cluster in the outskirts of the halo, a cloud of gas and dust in the outskirts of the diskour solar systemthe edge of the central bulge
Classify the given types of matter as either ordinary (baryonic) matter that contains protons and neutrons or as exotic (nonbaryonic) matter that consists of subatomic particles different from those that build atoms.
  • very high speed orbital motions around galactic nucleirapid changes in the luminosity of the galaxy nucleusquasars emit approximately equal power at all wavelengths from infrared to gamma raysthe discovery of powerful jets coming from a compact core
  • Ordinary (baryonic) matter:matter in our bodies,Matter in stars,matter in brown dwarfs,dark matter consisting of Jupiter-size objects in galactic halosExotic (nonbaryonic) matter:matter that probably makes up the majority of dark matter.dark matter consisting of weakly interacting subatomic particles.
  • Gas and dust are abundant in the disk but not in the halo.Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits.Clusters of young stars are found only in the disk.Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red.
  • Spiral arms are waves of higher density that move outward through a galaxy, triggering star formation as they pass.
Listed below are some characteristics of flat, spherical, and saddle-shaped geometries. Match each of these characteristics to the corresponding geometry.
  • From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
  • Flat Geometry: sum of angles of a triangle is always 180∘circumference of a circle is exactly 2πrSpherical Geometry:sum of angles of a triangle is greater than 180.straightest possible path is a segment of a great circle.lines that are initially parallel eventually convergeSaddle-Shaped Geometry: sum of angles of a triangle is less than 180∘lines that are initially parallel eventually diverge
  • Spirals: contain abundant clouds of cool gas and dust, are rare in central regions of galaxy clusters,contain many bright hot stars, have significant ongoing star formation, have a flattened disk of starsElliptical: contain primarily old, low-mass stars, are more reddish in color
  • the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies.observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies.observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy.observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
Astronomers suspect that 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. Each item below describes either a condition in a protogalactic cloud or a later interaction. Match these items to the galaxy type you would expect to form as a result.
  • Elliptical Galaxies: stars form rapidly as the protogalactic cloud shrinks.protogalactic cloud has high density.A galaxy collision strips away gas.Protogalactic cloud rotates very slowly.Spiral Galaxies: most protogalactic gas settles into a disk.Protogalactic cloud has high angular momentum.
  • Ordinary (baryonic) matter:matter in our bodies,Matter in stars,matter in brown dwarfs,dark matter consisting of Jupiter-size objects in galactic halosExotic (nonbaryonic) matter:matter that probably makes up the majority of dark matter.dark matter consisting of weakly interacting subatomic particles.
  • No. If all matter was ordinary, then the blue region representing the location of most of the matter would line up with the red region representing the hot gas.
  • Spirals: contain abundant clouds of cool gas and dust, are rare in central regions of galaxy clusters,contain many bright hot stars, have significant ongoing star formation, have a flattened disk of starsElliptical: contain primarily old, low-mass stars, are more reddish in color
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.
  • They all require rapid rotation , They are require very hot ionized gas,They all require hydrogen gas.
  • The X-ray source is no more than a few light-days in diameter.
  • Individual stars orbit around the center of the galaxy. Individual stars move in and out of spiral arms over time.
Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?
  • Because Hubble's law predicts that all galaxies outside our Local Group should be moving away from us.
  • warm, rarefied clouds of atomic hydrogen
  • stellar parallax ---- 1/arcsecond= parsecs
  • parallax, Cepheid variables, Hubble's law
What do astronomers consider heavy elements?
  • open clustersgas and dustold K and M starsO and B stars
  • we can observe its gravitational influence on visible matter.
  • It emits no or very little radiation of any wavelength.
  • all elements besides hydrogen and helium
Listed following are several locations in the Milky Way Galaxy. Rank these locations based on their distance from the center of the Milky Way Galaxy, from farthest to closest.
  • a globular cluster in the outskirts of the halo, a cloud of gas and dust in the outskirts of the diskour solar systemthe edge of the central bulge
  • an object with the same mass as the Sun but only half as large in radius
  • Flat Geometry: sum of angles of a triangle is always 180∘circumference of a circle is exactly 2πrSpherical Geometry:sum of angles of a triangle is greater than 180.straightest possible path is a segment of a great circle.lines that are initially parallel eventually convergeSaddle-Shaped Geometry: sum of angles of a triangle is less than 180∘lines that are initially parallel eventually diverge
  • 5 billion years, 2 billion light years, 800 million light years, 230 million light years, 70 million light years.
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Multiple Choice Questions
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