Deck 24: Quasars and Active Galaxies

Question 1

One of the three astronomical objects that were first detected at radio wavelengths by Grote Reber in the 1930s and 1940s was:

A)Cygnus
B)the Moon.
C)Jupiter.
D)the Sun.

Answer 1

A

Question 2

Where does the name quasar come from?

A)It comes from quasarium, the name given to the new element that was identified with the spectral lines before these were recognized as hydrogen with a very large redshift.
B)It is a contraction of "quasistellar radio source."
C)It is a contraction of "quantum pulsar," the original name.
D)It comes from Alfred

Answer 2

B

Question 3

The major surprise about Cygnus A, one of the first three sources of strong radio emission detected by Grote Reber in the late 1930s, when examined with a large optical telescope, was that it:

A)was at the center of our galaxy.
B)was a supernova remnant.
C)corresponded to no optical source at all.
D)was a relatively faint yet very distant object at optical wavelengths.

Answer 3

D

Question 4

All quasars appear to be:

A)moving in random directions, at high speeds.
B)very distant, intrinsically faint objects.
C)relatively close, very bright objects.
D)moving away from Earth at very high speeds.

Question 5

The typical optical spectrum of a quasar shows:

A)very redshifted emission lines superimposed upon a weak continuum of radiation.
B)a series of very blueshifted emission lines, with no continuum component.
C)a continuum of radiation crossed by a sequence of very redshifted absorption lines.
D)a sequence of highly blueshifted absorption lines upon a continuum of radiation.

Question 6

Astronomers initially had difficulty identifying the emission lines in quasar spectra at optical wavelengths because:

A)the lines are created by elements that do not exist on Earth.
B)no one expected violet and ultraviolet spectral lines to be shifted so far toward the red.
C)quasars are receding from us at extremely high speeds, and this smears out the emission lines, making them hard to measure.
D)they were emission lines from ionized atoms that had not been seen before.

Question 7

The emission lines in quasar spectra were difficult to identify at first because:

A)emission lines of such intensity were not expected from astronomical sources.
B)no one expected far-ultraviolet spectral lines to be shifted to visible wavelengths.
C)they were very faint and could not be measured accurately.
D)they arise from elements that do not exist on Earth.

Question 8

What is believed to be the status of quasars in the present universe?

A)A quasar is an evolutionary stage between spiral galaxies and giant ellipticals, and the evolutionary transformation is ongoing.
B)There are no quasars closer than about 800 million ly. Since their lifetimes are shorter than this, all have burned themselves out and are extinct.
C)Quasars appear only in very young galaxies. As a result, we find new quasars only in the centers of rich clusters where new galaxies are being formed.
D)Quasars date from an early time in the history of the universe when galaxies were more plentiful and collisions were more frequent-like the planetesimals in the early solar system. Quasars result from collisions of protogalaxies. This era of collisions has past and there are no more quasars.

Question 9

The unusual feature that was noted in the optical spectra of the faint starlike objects that coincided in position with the intense sources of radio energy known as quasars was:

A)sets of spectral lines that indicated simultaneous motion of sources toward and away from the Sun, possibly a rapidly expanding shell of material around the radio source.
B)the extreme redshift of emission lines that indicated high recessional velocities and hence great distances, requiring extremely high energy output in order to be detected.
C)the extreme blueshift, meaning that these stars in our galaxy are coming toward Earth at very high velocities.
D)the periodic variation of the Doppler shift from red to blue, indicating a light source oscillating back and forth over a few weeks.

Question 10

Active galactic nuclei (AGN) include a variety of objects, but all are powered by:

A)collisions between giant ellipticals.
B)the merger of black holes.
C)energy emerging through a wormhole from some other part of the universe.
D)hot gas accreting around a supermassive black hole.

Question 11

The recessional velocity of a distant quasar is measured to be 60% of the speed of light. This speed is large enough that we must take relativity into account in computing its distance, which proves to be 3290 Mpc. Suppose we just use the Hubble law (without taking into account relativity); what is the result?

A)779 Mpc
B)2470 Mpc
C)3290 Mpc
D)10,700 Mpc

Question 12

Suppose a distant quasar has a redshift of z = 0.3. To obtain the correct value of the distance at which one sees the object, one must use the relativistic formulas. These give an answer of 1020 Mpc. For comparison, what answer does the nonrelativistic calculation give?

A)120 Mpc
B)518 Mpc
C)1230 Mpc
D)1580 Mpc

Question 13

Suppose a distant quasar has a redshift of z = 3.0. To obtain the correct value of the distance at which one sees the object, one must use the relativistic formulas. These give an answer of 3500 Mpc. For comparison, what answer does the nonrelativistic calculation give?

A)120 Mpc
B)518 Mpc
C)1230 Mpc
D)12,300 Mpc

Question 14

The apparent brightness of the quasar 3C 273 is b = 2.22 × 10^-12 W/m². Its distance, from the Hubble relationship, is 2 billion ly. What is its luminosity (in watts)?

A)10³⁶
B)10³⁸
C)10⁴⁰
D)10⁴²

Question 15

The highest redshifts (z = Δλ / λ₀) that have been observed for quasars are in the range of:

A)z = 11 to 12.
B)z = 5 to 6.
C)z = 8 to 9.
D)z = 4 to 5.

Question 16

The lowest redshifts (z = Δλ / λ₀) commonly observed for quasars are approximately:

A)z = 0.3.
B)z = 0.8.
C)z = 1.2.
D)z = 2.5.

Question 17

At what distance do we see a quasar having a redshift of z = 3.0? (See Figure 24-4 of Universe, 11th ed.(in the text))

A)1.63 billion ly
B)4.89 billion ly
C)8.15 billion ly
D)11.4 billion ly

Question 18

The quasar PKS 1247+3406 has a redshift z = 4.897. What is its recession speed away from our galaxy?

A)4.897c
B)2.06c
C)1.204c
D)0.94c

Question 19

The hydrogen Balmer H $\alpha$ line with laboratory wavelength 656.3 nm is identified in emission in the spectrum of a quasar at 1968.9 nm. What is its velocity with respect to us?

A)0.8c toward us
B)0.8c away from us
C)1.2c toward us
D)1.2c away from us

Question 20

The hydrogen Balmer H $\alpha$ line with laboratory wavelength 656.3 nm is identified in emission in the spectrum of a quasar at 1968.9 nm. What is its redshift?

A)z = 0.3
B)z = 1.0
C)z = 2.0
D)z = 3.0

Question 21

The spectrum of the quasar PKS 2000-330 contains the UV Lyman L_α line (λ₀ = 121.6 nm), which has been shifted into the visible region of the spectrum by a redshift of z = 3.773. What is the shift, Δλ₀, of this radiation in nanometers?

A)45.85 nm
B)458.5 nm
C)701.5 nm
D)635 nm

Question 22

The redshift of quasar 3C 273 is z = 0.158. What is the wavelength of the H $\gamma$ line ( $\lambda$ ₀ = 434 nm) in the spectrum of this quasar?

A)68.5 nm
B)365 nm
C)503 nm
D)669 nm

Question 23

The energy output of a bright quasar is equivalent to:

A)1000 times that of the Sun.
B)10⁶ solar-type stars.
C)that of the Milky Way Galaxy.
D)1000 bright galaxies.

Question 24

How do we determine the distance to a quasar?

A)Quasars are all essentially identical and thus act as standard candles. We can determine the distances to the nearer ones because they contain variable stars, and the distance to a farther quasar can then be determined from its brightness.
B)Quasars contain Cepheid variables.
C)The Tully-Fisher relation is used.
D)The Hubble velocity-distance relation is used once spectroscopy gives a redshift value.

Question 25

The quasar 3C 273 is believed to have a luminosity of about 2.5 × 10¹³ L_e at a distance of 620 Mpc. Suppose instead that it were a normal galaxy with a luminosity 1000 times smaller. How far away would it have to be to have the same apparent brightness it has now?

A)620 kpc
B)6.2 Mpc
C)19.6 Mpc
D)620 × 10⁹ pc

Question 26

The flickering of an AGN allows one to calculate the size of the source. This is actually the size of the:

A)host galaxy.
B)accretion disk around the black hole.
C)event horizon of the black hole.
D)central bulge of the host galaxy.

Question 27

An object with a diameter of 4 ly emits a sudden flash of light. On Earth this brightness change is seen to evolve over a period of:

A)2 years.
B)4 years.
C)8 years.
D)16 years.

Question 28

The time of variation in the brightness of quasars can be as short as:

A)a few seconds.
B)about a month.
C)about a year.
D)less than a day.

Question 29

Relatively rapid fluctuations (within 1 day) in the electromagnetic output of quasars is an indication of:

A)objects moving in front of them from our point of view.
B)the rapid rotation of the sources.
C)the relatively small size of the emitting regions.
D)their relative closeness to the Milky Way.

Question 30

What observational fact convinces astronomers that the source of energy in a typical quasar is physically very small?

A)the extremely high redshift of its spectrum
B)the appearance of all quasars as starlike objects in our sky
C)the extreme distance of all quasars
D)the rapid variation of the intensity of the source

Question 31

Why is it that, when we observe an extragalactic source whose diameter is about 1 light-day, we are unlikely to see fluctuations in light output in times shorter than about 1 day?

A)because the light from different parts of the source will be Doppler shifted by different amounts, allowing us to see only an average shift
B)because light from the back of an object, 1 light-day further from us than the front, cannot be received by us earlier than 1 day after the front
C)because absorption of light by intergalactic matter will smooth out rapid fluctuations within the beam
D)because it is inconceivable that a source of this size could vary on such a short time scale

Question 32

The surprising observational fact about quasars is that they appear to:

A)be the largest known structures in the universe, although they produce only modest amounts of energy.
B)be moving rapidly toward us, while emitting large amounts of energy.
C)be associated with ancient supernova explosions.
D)produce the energy output of 1000 galaxies in a volume similar to that of our planetary system.

Question 33

Which observational fact about quasars and their behavior is perhaps the most extraordinary?

A)velocities of recession of up to 9/10 of the speed of light
B)distances from the Sun of up to 18 billion ly
C)incredibly powerful radio emitters, such that simple receivers can detect them, from vast distances across the universe
D)energy output equivalent to 1000 galaxies from a volume as small as our planetary system

Question 34

How do we measure or calculate the size of the black hole in the center of a quasar?

A)Observe a star moving around the black hole and use Kepler's third law to calculate the central mass.
B)Measure directly the size of the dark area corresponding to the black hole.
C)Use the Eddington radiation limit.
D)Watch a star fall through the event horizon and measure its acceleration.

Question 35

The Sun's luminosity would have to increase by how many times for it to reach its Eddington limit?

A)30,000
B)1000
C)The Sun, like all main sequence stars, it already at its Eddington limit.
D)The Eddington limit does not apply to stars.

Question 36

What would the mass of a supermassive black hole at the center of a quasar need to be, in terms of the solar mass, in order to produce a luminosity of 10¹² times that of our Sun, assuming that this luminosity is at the Eddington limit?

A)10⁹
B)3.3 × 10⁷
C)10¹²
D)3.3 × 10⁸

Question 37

The distant quasar ULAS J1120+0641 has a luminosity 6 × 10¹³ L_e. Assuming it is at its Eddington limit, what is its mass (in solar masses)?

A)30,000
B)2 million
C)2 billion
D)6 billion

Question 38

The distant quasar ULAS J1120+0641 has a mass 2 × 10⁹ M_e. Assuming it is at its Eddington limit, what is its luminosity (in solar luminosities)?

A)30,000
B)2 x 10⁶
C)6 x 10⁹
D)6 x 10¹³

Question 39

The luminosity of the Milky Way Galaxy is about 3 × 10¹⁰ L_e. Suppose all of this luminosity is due to a black hole and accretion disk at the center of the galaxy that is assumed to be at its Eddington limit. What would this suggest the mass is of this black hole (in solar masses)?

A)30,000
B)3 × 10⁵
C)10⁶
D)3 × 10¹⁰

Question 40

The quasar 3C 273 has a luminosity about 25 trillion times that of the Sun. Assuming this is the Eddington limit, what is the minimum mass of the active galactic nucleus (stated in solar masses)?

A)8.5 million
B)25 million
C)850 million
D)8.5 billion

Question 41

A radio galaxy is any galaxy that:

A)has two lobes, one on each side of the galaxy, which emit synchrotron radiation at radio wavelengths.
B)emits large amounts of energy from the whole galaxy at radio wavelengths.
C)is invisible at optical wavelengths (ordinary light) and detected only at radio wavelengths.
D)has a bright, compact nucleus that emits large amounts of thermal energy at radio wavelengths.

Question 42

The most likely mechanism for the many double radio sources that are now detected in distant space is:

A)two oppositely directed jets of matter, ejected from a small source in the center of a galaxy.
B)two pulsars on opposite sides of a quasar.
C)two black holes on either side of a small galactic nucleus.
D)two radio stars in the spiral arms of a galaxy, symmetrically placed around the galactic nucleus.

Question 43

As matter swirls inward in the accretion disk surrounding an AGN, the pressure increases enormously. One consequence of this is:

A)the formation of jets of material pushing outward perpendicular to the plane of the disk.
B)that the event horizon of the black hole is pushed inward.
C)a supernova eruption.
D)an outward expansion of the size of the accretion disk.

Question 44

The jets associated with AGN are defined by intense magnetic fields. What is the origin of these magnetic fields?

A)The stars that formed the black hole had magnetic fields, and the black hole retains those fields.
B)The accretion disk contains a plasma of charged particles. The acceleration of these particles produces a magnetic field.
C)The intense gravity of the black hole attracts and concentrates the magnetic field associated with the host galaxy as a whole.
D)Friction between the inner and outer parts of the rotating accretion disk produce the magnetic fields.

Question 45

In order to appear superluminal, a few conditions must be satisfied by the material under observation. One of these is that:

A)the material must consist of neutrinos that can, in fact, exceed the speed of light.
B)the material must be moving directly away from us.
C)the material must be moving close to the speed of light.
D)we must be able to isolate a single wavelength, usually 21 cm, for observation.

Question 46

The apparent motion of objects at speeds greater than that of light ("superluminal motion") is caused by:

A)objects moving almost directly toward us at speeds close to (but less than) that of light.
B)gravitational lensing.
C)objects moving almost directly toward us at speeds greater than that of light.
D)the expansion of space, carrying distant galaxies away from us at apparent speeds greater than that of light.

Question 47

To what does the phrase "superluminal motion" refer?

A)the motion of relativistic electrons in magnetic fields
B)the apparent motion of jets of gas at speeds faster than light
C)the apparent motion of arcs of light caused by gravitational lensing
D)the motion of galaxies at redshifts z > 1

Question 48

Consider the diagram of superluminal motion in Figure 24-11 of Universe, 11th ed. Suppose the motion of the blob of material continued on in a straight line at 5/6c for an additional 5 years to position C. Viewed from Earth, the speed of the blob would then appear to be:

A) 5/6c.
B) 11/12c.
C) 1.5c.
D) incalculable. In this case the light from the final position C would arrive at Earth before the light from the initial position A.

Question 49

The accretion disk around a typical quasar is about the size of:

A)the Sun.
B)Earth's orbit.
C)the solar system.
D)the central bulge of the Milky Way Galaxy.

Question 50

As currently understood, the ultimate source for the tremendous energy output of an AGN is:

A)nuclear fusion.
B)nuclear fission.
C)E = mc².
D)gravitational potential energy.

Question 51

Seyfert galaxies were once considered to be a distinct class of galaxies because they:

A)are completely devoid of structure, appearing to be amorphous spheres of gas and dust.
B)are in the constellation of Seyfert in the southern hemisphere sky.
C)are very close to the Milky Way and appear to be gravitationally bound to it.
D)have hot and very bright and variable, compact central cores.

Question 52

Seyfert galaxies are:

A)elliptical galaxies whose nuclei resemble quasars.
B)spiral galaxies whose nuclei resemble quasars.
C)giant irregular galaxies that have neither spiral arms nor the smooth shape of elliptical galaxies.
D)active galaxies, most of whose energy is emitted at radio wavelengths by two widely spaced lobes above the galactic poles.

Question 53

Among galaxies with active galactic nuclei, Seyfert galaxies are:

A)spiral galaxies with strong radio emission.
B)spiral galaxies with weak radio emission.
C)elliptical galaxies with strong radio emission.
D)elliptical galaxies with weak radio emission.

Question 54

A spiral galaxy with a bright, compact nucleus showing strong emission lines is called a:

A)quasar.
B)gravitational lens.
C)blazar.
D)Seyfert galaxy.

Question 55

What is the difference between a Seyfert galaxy and other AGNs?

A)Seyferts are always spirals; other AGNs are always elliptical.
B)Seyferts always have broad emission lines; other AGNs can have lines that are broad or narrow.
C)Seyferts are basically like other AGNs, only closer to us.
D)Seyferts are the only radio-loud AGNs that are spirals.

Question 56

Observationally, the biggest difference between quasars and other active galaxies such as Seyferts and radio galaxies appears to be that:

A)Seyferts and radio galaxies have bright nuclei, but do not have ejected jets of material from their nuclei.
B)quasars appear to be located inside elliptical galaxies, whereas Seyferts and radio galaxies are all inside spirals.
C)Seyferts and radio galaxies do not have the bright, starlike nuclei of quasars.
D)Seyferts and radio galaxies are less powerful than quasars.

Question 57

Blazars are:

A)elliptical galaxies whose nuclei resemble quasars.
B)spiral galaxies whose nuclei resemble quasars.
C)giant irregular galaxies that have neither spiral arms nor the smooth shape of elliptical galaxies.
D)active galaxies, most of whose energy is emitted by two widely spaced radio lobes.

Question 58

A blazar is a(n):

A)eclipsing binary star in which one component is believed to be a neutron star or a black hole.
B)rapidly spinning neutron star.
C)active galactic nucleus.
D)emission nebula containing a young T Tauri star.

Question 59

The spectrum of a blazar shows:

A)absorption lines of highly ionized atoms.
B)doubled emission lines split by the Doppler shift of oppositely directed jets of material.
C)strong, highly redshifted emission lines.
D)a continuum with very faint emission and absorption lines that are all but rendered invisible by the intense radio radiation.

Question 60

A starlike object showing an almost featureless continuum spectrum would be a:

A)gravitational lens.
B)quasar.
C)Seyfert galaxy.
D)blazar.

Question 61

Active galaxies include each of the following EXCEPT:

A)quasars.
B)blazars.
C)Seyfert galaxies.
D)irregular galaxies.

Question 62

A radio galaxy, viewed from a position so that the observer is looking down one of the jets toward the galaxy, is a:

A)blazar.
B)quasar.
C)Seyfert Type 1 galaxy.
D)Seyfert Type 2 galaxy.

Question 63

Recent evidence indicates that quasars:

A)are isolated objects not associated with galaxies.
B)occur only in elliptical galaxies.
C)occur only in spiral galaxies.
D)occur in both spiral and elliptical galaxies.

Question 64

What is the relationship between blazars (intense, rapidly varying nonthermal sources of polarized radio radiation) and double-lobed radio sources?

A)A blazar is an early view of a superluminous supernova, which will eventually evolve into a double radio source as matter expands outward.
B)A blazar appears to be what is left in space after all the surrounding matter has been devoured by a black hole, whereas a double radio source still has matter spiraling into the black hole.
C)A blazar is now considered to be the end-on view of a double radio source, looking along one of the relativistic particle jets emitted from the central core.
D)A blazar is the central "engine" that generates the energy for the relativistic particle beams that produce the double radio lobes.

Question 65

If double radio sources, quasars, and blazars are considered to be the same basic object, why do they appear to us to have very different and distinct properties?

A)because the relativistic particles in the double jets are different in each case: electrons in double radio sources, protons in quasars, and quarks in blazars
B)because they are at different distances from us, and we see more detail and different properties on those that are closer to us
C)because we are viewing them at different angles to the line of the double jets emitted from their cores
D)because they are of different ages

Question 66

In the "unified model" of active galaxies, the main difference among quasars, blazars, and radio galaxies appears to be that:

A)the mass of the central black hole is different in each case-largest in quasars, less in blazars, and least in radio galaxies.
B)the rate at which matter is falling into the central black hole is different in each case-highest in quasars, less in blazars, and lowest in radio galaxies.
C)the galaxy type is different in each case-spiral for blazars, elliptical for quasars, and irregular for radio galaxies.
D)we see the accretion disk around the central black hole from a different angle in each case-face on for blazars, edge on for radio galaxies, and in between for quasars.

Question 67

Quasars, blazars, and double radio sources may well be the same kind of object, their different appearance simply being caused by their:

A)age: BL Lac objects that evolve through a double radio source phase end up as a quasar.
B)orientation: In blazars the jets point toward and away from us, in double radio sources they point sideways, and quasars are in between.
C)position in the universe: Quasars are in our galaxy, double radio sources are associated with other galaxies, and BL Lac objects are within the vast voids of space between galaxies.
D)size: Quasars are star sized, double radio sources are larger, and BL Lac objects are galaxy sized.

Question 68

Suppose a rotation curve is made of the region close to the center of a galaxy. At a distance of 4 pc from the center the radial velocity is 328 km/sec. How much mass is within this 4-pc radius (in solar masses)?

A)10⁶
B)10⁸
C)2.4 × 10¹¹
D)1.2 × 10¹⁷

Question 69

What is the lifetime of the average quasar?

A)less than 1 million years
B)a few tens of millions of years
C)a few hundred million years
D)several billion years

Question 70

Why are there no nearby (and thus "young") quasars?

A)Eventually, most of the accretion disk falls into the black hole and the "central engine" runs out of fuel.
B)The central black hole eventually consumes the entire galaxy, and with no more matter in the vicinity, it becomes dormant until another galaxy happens to pass nearby.
C)The continual infall of material causes the mass of the black hole to grow until it explodes, resulting in a supernova.
D)The immense radiation output from the quasar carries away energy. The mass of the black hole gets smaller until it evaporates.

Question 71

Where do Seyfert galaxies fit into the unified and accretion disk models for AGN?

A)Seyferts are young active galaxies that have not yet become quasars.
B)Seyferts are former quasars that have become less active as a result of depletion of the source material needed to sustain the accretion disk around the central black hole.
C)Seyferts are what we observe when looking at an active galaxy without jets.
D)When an active galaxy has its accretion disk oriented so that the jets lie in the plane of the galaxy rather than perpendicular to it, the beams of synchrotron radiation can generate spiral arms, and the galaxy becomes a Seyfert.

Question 72

What is the end for a typical quasar?

A)The black hole at the center of the quasar pulls in more and more mass from the host galaxy until everything has fallen into the black hole and nothing visible remains.
B)The tremendous inrush of matter at the Eddington limit produces a supernova explosion, leaving a galaxy with a halo of supernova remnants.
C)The black hole eventually consumes all nearby fuel and becomes a dormant black hole, called a dead quasar, at the center of the still-functioning galaxy.
D)Quasars are long lived, and we have no evidence on which to base a picture of how they end.

Question 73

What is a dead quasar flare?

A)the last flicker of a dying black hole before it becomes dormant
B)the result of a star being consumed by a dormant black hole
C)the large burst of light emitted when two black holes (former quasars) collide and merge
D)the bright flash of light that occurs when one of the jets from a dying quasar sweeps over Earth