Milky Way
What is the significance of the object Sagittarius A* ("Sagittarius A-star") in our Galaxy? It appears to be a jet of material ejected from an accretion disk around a supermassive black hole in the galactic nucleus. It is a globular cluster passing close to the galactic nucleus, and the RR Lyrae stars in it allow the distance to the galactic center to be calculated. It is a bright, high-speed cloud of gas close to the galactic nucleus, which allows the mass of the nucleus to be calculated. It appears to be the actual nucleus of the Galaxy.
It appears to be the actual nucleus of the Galaxy.
Do the shapes of elliptical galaxies really reflect their true shape? No, they may all be the same shape but viewed either edge-on, face-on, or in between these two cases. Yes. The shapes we see have been shown to be their true three-dimensional shape. No, because we cannot see the outlying spherical shells of material detected by radio telescopes around elliptical galaxies. No. The shapes of most of them have been severely distorted by gravitational lensing around the super-massive black hole at their centers.
No, they may all be the same shape but viewed either edge-on, face-on, or in between these two cases.
The Hubble classification for a spiral galaxy with a prominent central bulge and tightly wound spiral arms directly connected to the central bulge is Sa. SBa. Sc. E0.
Sa.
The Milky Way Galaxy appears to have a spiral structure with one "arm," wound around the nucleus four times. at least four separate major arms. three loosely wound arms. two major arms, wound twice around the nucleus.
at least four separate major arms.
Which of the following best describes of the object at the center of our Galaxy? several trillion solar masses in a volume two light-years in diameter 20 solar masses in a volume the size of the Sun 4 million solar masses in a volume the size of our solar system 5 billion solar masses in a volume smaller then Jupiter's orbit
4 million solar masses in a volume the size of our solar system
What quantum transition occurs inside a cool hydrogen atom to produce a 21-cm radio photon? The electron combines with the proton in the nucleus to become a neutron, producing energy. An electron reverses the direction of its motion in orbit around the proton. An electron falls from the level n = 100 to the level n = 99 in the atom. An electron in the ground atomic state reverses its direction of spin with respect to that of the proton.
An electron in the ground atomic state reverses its direction of spin with respect to that of the proton.
What do we know about the geometry of the dark matter distribution in the vicinity of the Milky Way Galaxy? It appears to be a lens-shaped disk like the Galaxy's disk of visible stars, only larger. It appears to be a spherical halo. The geometry of the dark matter distribution, like its constituents, is totally unknown at the present time. Dark matter, including that near the Milky Way Galaxy, appears to be part of a uniform density distribution that fills all of space.
It appears to be a spherical halo.
If the galactic center is now thought to contain a supermassive black hole, why is the Sun not falling into it under the black hole's extreme gravity? because its mass is so small that even this extreme mass concentration at the galactic center will not exert a significant force on it because the mutual gravitational forces of local stars in the Orion spiral arm are sufficient to overcome the strong inward force and keep the Sun moving in its orbit because it has sufficient velocity that it can orbit the galactic center in a circle because the inward force exerted on the Sun from the black hole is offset by the force exerted outward by the hidden "dark" matter beyond the Sun's orbit
because it has sufficient velocity that it can orbit the galactic center in a circle
How is the mass of the Galaxy estimated? by observing its movement toward neighboring galaxies because of gravitational attraction by counting stars and assuming an average stellar mass by observing the bending of light from distant galaxies as it passes near the Milky Way center by applying Newton's extension of Kepler's laws to the motion of the Sun and other stars
by applying Newton's extension of Kepler's laws to the motion of the Sun and other stars
The density wave that produces the spiral arm in the Milky Way Galaxy is similar in properties to a compression wave. wave on a stretched string. gravitational wave. light wave.
compression wave.
Hubble's law describes how two properties of distant galaxies are related to each other. What are these two properties? distance and brightness brightness and the width of the 21-cm radio emission line of hydrogen distance and velocity of recession brightness and recession velocity
distance and velocity of recession
Variable stars, such as Cepheid variables and RR Lyrae stars, are used in what important measurement in astronomy? distance measurement surface temperature measurement the keeping of accurate time rotation speeds of galaxies
distance measurement
Recent evidence suggests that larger galaxies formed from the collapse of immense clouds of gas and dust. from the mergers of smaller objects. when clouds of dark matter coalesced. as direct, immediate products of the Big Bang.
from the mergers of smaller objects.
A lobe radio galaxy is any galaxy that emits large amounts of energy from the whole galaxy at radio wavelengths. has a bright, compact nucleus that emits large amounts of thermal energy at radio wavelengths. has regions, one on each side of the galaxy, which emit synchrotron radiation at radio wavelengths. is invisible at optical wavelengths (ordinary light) and detected only at radio wavelengths.
has regions, one on each side of the galaxy, which emit synchrotron radiation at radio wavelengths.
A rich, regular cluster of galaxies differs from a rich, irregular cluster by lacking the giant elliptical galaxies often found in irregular clusters. containing fewer galaxies than an irregular cluster. having fewer spirals and more ellipticals and S0 galaxies than an irregular cluster. having its galaxies distributed in a regular, highly flattened system (like a disk).
having fewer spirals and more ellipticals and S0 galaxies than an irregular cluster.
Active Galactic Nuclei (AGN) include a variety of objects, but all are powered by the merger of black holes. hot gas accreting around a supermassive black hole. energy emerging through a wormhole from some other part of the universe. collisions between giant ellipticals.
hot gas accreting around a supermassive black hole.
Where is the Sun located in our Galaxy (i.e., what is our address in the universe)? in or close to the Orion arm, which is between the Sagittarius and Perseus arms in the Sagittarius arm, which is between the Centaurus and Orion arms in the Centaurus arm, between the galactic center and the Orion arm in the Perseus arm, between the Orion and Cygnus arms
in or close to the Orion arm, which is between the Sagittarius and Perseus arms
Galactic cannibalism is seen most often in everywhere in the universe in rich irregular clusters in poor clusters in rich galaxy cluster
in rich galaxy cluster
Where is the solar system located in our Galaxy? in the galactic nucleus in the galactic halo in the galactic disk It is not in a galaxy, but in intergalactic space.
in the galactic disk
Quasars increase in number as redshift increases, a relationship that persists to the highest redshifts we can measure. are extinct. are more common in nearby clusters of galaxies and less common in distant clusters of galaxies. are rare in the Local Group, with only one or two examples.
increase in number as redshift increases, a relationship that persists to the highest redshifts we can measure.
The center of our Milky Way Galaxy can be observed most easily at which of the following wavelengths? infrared and radio radiation. highly penetrating gamma rays. red hydrogen light. ultraviolet light.
infrared and radio radiation.
The Magellanic Clouds seen from the southern hemisphere are examples of what type of objects? irregular galaxies lenticular galaxies planetary nebulae globular clusters
irregular galaxies
One of the big puzzles about the properties and behavior of large clusters of galaxies is that each one appears to consist of the same type of galaxy, some made up totally of spiral galaxies whereas others contain only ellipticals. they appear not to take part in the general expansion of the universe, in contrast to single separate galaxies, probably because they are gravitationally bound to one another. there appears to be insufficient mass in the luminous matter (star, etc.) to hold the cluster together gravitationally. they appear to be spread uniformly throughout space in all directions, which is difficult to explain with the Big Bang Theory.
there appears to be insufficient mass in the luminous matter (star, etc.) to hold the cluster together gravitationally.
When distances were carefully measured from Earth to globular clusters above and below the Milky Way plane (where our view of them is not obscured by interstellar dust and gas), their distribution was found to be uniformly distributed throughout space, with no concentration in any area of the Milky Way Galaxy. in a relatively flat disk almost perpendicular to the plane of the Galaxy, with relatively higher density of clusters toward its center. concentrated in the plane of the Milky Way and clustered around the Sun's position, indicating that the Sun is close to the Galaxy's center. spherically symmetric about a point in the constellation Sagittarius and concentrated in that direction.
spherically symmetric about a point in the constellation Sagittarius and concentrated in that direction.
Seyfert galaxies are elliptical galaxies whose nuclei resemble quasars. spiral galaxies whose nuclei resemble quasars. active galaxies, most of whose energy is emitted at radio wavelengths by two widely spaced lobes above the galactic poles. giant irregular galaxies that have neither spiral arms nor the smooth shape of elliptical galaxies.
spiral galaxies whose nuclei resemble quasars.
The Tully-Fisher Relationship can be used to measure the luminosity of (and thus the distance to) elliptical galaxies. Type II supernovae. globular clusters. spiral galaxies.
spiral galaxies.
Which component of our galaxy has the shape of a football? the bulge the halo the disk all components have this shape
the bulge
Which components of our galaxy have random motions? the halo only the bulge and halo the bulge and disk the bulge only
the bulge and halo
Which of the following main components of our galaxy have a reddish color? all components have this color the disk the halo the bulge
the halo
Astronomers have found the existence of spiral arms in galaxies difficult to account for because the arms should have been destroyed by collisions with other galaxies over the galaxy's lifetime. the outer regions of a galaxy including the spiral arms have no significant rotation, so the arms should have fallen into the center of the galaxy. the outer parts of a galaxy rotate faster than the inner parts, so the arms should have straightened out into spokes like those of a bicycle wheel. the inner part of a galaxy rotates in a shorter time than the outer parts, so the arms should have wound up so tightly that they would have disappeared over the lifetime of the galaxy.
the inner part of a galaxy rotates in a shorter time than the outer parts, so the arms should have wound up so tightly that they would have disappeared over the lifetime of the galaxy.
The primary evidence for the expanding universe concept is the slow increase with time of the separation between Earth and the Moon. the redshift of light from distant galaxies, which increases with distance of the galaxy from Earth. observation of supernova explosions. the discovery of black holes in binary stars.
the redshift of light from distant galaxies, which increases with distance of the galaxy from Earth.
What fraction of the mass required by the cluster's observed gravity, as shown by the speeds of galaxies in the cluster, is represented by the mass of the presently observable matter in a typical rich cluster of galaxies? 90% 10% about 1% 100%, or all of the galaxy
10%
What is the luminosity of a Cepheid variable star with a pulsation period of 5 days compared to the Sun? (Hint: use the Period-Luminosity Relationship Plot) 5000x 100x 1000x 10000x
1000x
Given that the Milky Way is 100,000 light years across and assuming that the Andromeda galaxy is at a distance of 2 million light years, how many Milky Way diameters separate the Milky Way and Andromeda? 20 100 50 10
20
The spiral-arm structure of the Milky Way Galaxy has been measured and evaluated most effectively by observations of UV radiation from hot hydrogen gas. red emission lines of visible radiation from hydrogen. 21-centimeter radiation from interstellar hydrogen and the positions of young stars. globular clusters in the halo of the Galaxy.
21-centimeter radiation from interstellar hydrogen and the positions of young stars.
The time taken for the Sun to orbit the galactic center once in its motion in the Galaxy is 2.3 million years. about 1/2 million years. 1.3 × 1011 years. 225 million years.
225 million years.
Why are we able to see only a small part of our Galaxy, the Milky Way Galaxy? Distant stars are obscured by gas in interstellar space. Distant stars are obscured by dust in interstellar space. There are so many stars in our Galaxy that the more distant ones are hidden behind the nearer ones. Expansion of the universe has carried the more distant stars out of our view.
Distant stars are obscured by dust in interstellar space.
A spiral density wave is like a stalled truck on the freeway. True False
False
A spiral density wave moves with the disk of a galxy. False True
False
After the Milky Way formed, the stars in the halo fell into the disk. False True
False
Collisions between galaxies can be observed in real time. True False
False
Stars in the halo of our galaxy have stronger absorption lines due to heavy elements. True False
False
The "Quasar Epoch" continues to this day. False True
False
The Local Group is the largest galaxy cluster in our local supercluster. True False
False
The Milky Way formed from one giant cloud of protogalactic gas. False True
False
The Milky Way is spherical. True False
False
The first stars to form in the Milky Way were in the disk. True False
False
The supermassive balck hole at the center of the Milky Way is larger than average for a galaxy of its size. False True
False
The voids seen between superclusters are completely empty. False True
False
WIMPs are associated with baryonic dark matter. True False
False
Most galaxies observed at high redshifts in the Hubble deep field images are small irregular galaxies large irregular galaxies giant elliptical galaxies small spiral galaxies
small irregular galaxies
Who was the first to look at the Milky Way with a telescope? Galileo Galilei Johannes Kepler Sir William Herschel Sir Isaac Newton
Galileo Galilei
In 1785, William Herschel proposed that the solar system was at the center of the Milky Way Galaxy. How did he reach this conclusion? Like the ancient Greeks and many of their successors for over a thousand years, Herschel based his conclusion on the philosophical importance of Earth in the cosmos. Herschel determined that Cepheid variable stars in the Milky Way Galaxy were distributed uniformly around Earth. Herscel's observations suggested that the stars in the Milky Way Galaxy were distributed uniformly around Earth. Herschel measured distances to globular clusters and determined that they were distributed uniformly around Earth.
Herscel's observations suggested that the stars in the Milky Way Galaxy were distributed uniformly around Earth.
The distances to galaxies in redhsift surveys are measured using the Tully-Fisher relation Cepheid variable stars Hubble's Law Type Ia supernova explsoions
Hubble's Law
The idea that some of the "nebulae" that are observed in the sky might be "island universes"—immense collections of stars far beyond the Milky Way—was first proposed by Immanuel Kant. Heber Curtis. Lord Rosse. Edwin Hubble.
Immanuel Kant.
Even though the Hubble law for galactic motions indicates that the spectra of all galaxies should show redshift as a consequence of the general expansion of the universe, the Andromeda Galaxy M31 appears to show a blueshift in its spectrum. Why is this? The peculiar motion of M31 has overcome the general Hubble flow. One side of M31 is heavily obscured by dust and gas and the blueshift simply shows the Doppler shift of the other side of the galaxy, produced by galactic rotation. M31 has an abnormally powerful black hole at its center that gravitationally blueshifts its entire spectrum. Young giant spiral galaxies such as M31 do not follow the normal Hubble flow because they have formed relatively recently.
The peculiar motion of M31 has overcome the general Hubble flow.
How many large spiral galaxies are there in the Local Group of galaxies? The Milky Way Galaxy is the only one. There are only two, Andromeda and the Milky Way. There are three. We really don't know how many because some could be hidden unseen on the other side of our Galaxy, cut off from our view by clouds of gas and dust.
There are three.
After colliding the Milky Way and Andromeda galaxies will probably merge into a single larger galaxy. False True
True
Einstein rings are only seen when a distant galaxy and the lensing galaxy are in perfect alignment. False True
True
Most if not all bright galaxies have supermassive black holes. True False
True
Most supermassive black holes formed from the mergers of smaller black holes. False True
True
Self-propagating star formation can only account for the formation of short segments of spiral arms. True False
True
Supercluster filaments are the largest structures in the local universe. False True
True
The Milky Way can be seen from every location on Earth (assuming no light pollution). True False
True
The Sun is a Population I star. True False
True
The conservation of angular momentum resulted in the formation of the Milky Way's disk. True False
True
The overall shape of galaxies suggest that they form in a similar manner to stars but on a larger scale. True False
True
What is a barred spiral galaxy? a galaxy with a bar through the nuclear bulge, and the spiral arms starting from the ends of the bar a spiral galaxy with a straight bar instead of a nuclear bulge a galaxy in which the arms form straight bars instead of spiral curves a galaxy with a bar extending across the entire diameter and the arms starting at intervals along the bar
a galaxy with a bar through the nuclear bulge, and the spiral arms starting from the ends of the bar
The major merger between two Quasars produces a radio galaxy an irregular galaxy a normal spiral galaxy a normal elliptical galaxy
a radio galaxy
What type of object has been proposed to explain the tremendous activity detected at the center of our Galaxy? a rapidly rotating neutron star a supermassive black hole a giant molecular cloud a supernova explosion
a supermassive black hole
In size, the Milky Way Galaxy is one of the smallest galaxies, with few others known to be much smaller. virtually the entire universe, with very few objects known to be outside it. a typical galaxy, with many others known to be larger and many known to be smaller. one of the largest galaxies, with no other galaxy known to be much larger.
a typical galaxy, with many others known to be larger and many known to be smaller.
In the verification of the Hubble law for the expansion of the universe and the determination of the constant H0, the greatest difficulty has been allowance for the fact that the high gravitational fields of the supermassive black holes within distant galaxies can redshift light (gravitational redshift). identification of distant objects as galaxies, rather than very bright stars. measurement of recession velocities of distant galaxies by Doppler shift. accurate determination of distances to very distant galaxies.
accurate determination of distances to very distant galaxies.
Radio waves of 21-cm wavelength originate from which component of the interstellar medium? molecular hydrogen, H2 neutral atomic hydrogen carbon monoxide, CO ionized atomic hydrogen
neutral atomic hydrogen
The method used by Hubble to determine the distance to the Andromeda Galaxy (M31), thereby establishing the concept of separate and individual galaxies throughout the universe, was the measurement of the redshift of the whole galaxy. observation of the apparent brightnesses of supernovas in M31. observation of Cepheid variable stars. measurement of stellar parallax, or apparent motion of stars because of Earth's orbital motion.
observation of Cepheid variable stars.
Our Galaxy is one member of a small cluster of galaxies. an isolated galaxy, not a member of any cluster. one member of a large, irregular cluster of thousands of galaxies. one member of a large, regular cluster of thousands of galaxies.
one member of a small cluster of galaxies.
Which two parameters of star motion in the Milky Way are represented by its rotation curve? orbital speed as a function of star distance from the galactic center star position above or below the galactic plane as a function of distance from the galactic center orbital period of the stars as a function of their distance from the galactic center orbital speed of the stars as a function of their age
orbital speed as a function of star distance from the galactic center
In the Hubble Classification Scheme for spiral galaxies, the tightness of the winding of the spiral arms appears to be directly related to the overall intrinsic size of the galaxy, or the diameter across the spiral arms. number of globular clusters in the halo of the galaxy. age of the galaxy, as determined from the age of its individual stars. size of the central bulge of the galaxy.
size of the central bulge of the galaxy.
Quasars appear to be relatively close, very bright objects moving away from Earth. very distant, intrinsically faint objects, moving toward Earth very rapidly. very distant, intrinsically bright objects, moving away from Earth at very high speeds. very distant and intrinsically bright objects moving in random directions at high speeds.
very distant, intrinsically bright objects, moving away from Earth at very high speeds.
The dimensions of our Galaxy are not precisely known. For example, our distance to the galactic center is known only to 8±1 kpc. One fundamental reason for this lack of further knowledge is that we are inside the Galaxy. the Milky Way Galaxy is an irregular galaxy without much uniformity. our detection systems are not powerful enough to see across the entire Galaxy. the whole system rotates rapidly, making measurements difficult.
we are inside the Galaxy.
Which of the following fundamental astronomical questions did Curtis and Shapley debate in 1920 in their famous confrontation? whether the spiral "nebulae" were part of the Milky Way Galaxy or more distant, separate entities whether the universe was expanding outward in all directions whether the Theory of General Relativity could be used to explain the behavior of our universe whether the Sun was at the center of the Milky Way Galaxy
whether the spiral "nebulae" were part of the Milky Way Galaxy or more distant, separate entities