Question 1

How do we determine the distance to a quasar?

Accepted Answer

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.E) A) and C)
F) All of the above

Question 2

A radio galaxy is any galaxy that:

Accepted Answer

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.E) A) and D)
F) A) and C)

Question 3

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

Accepted Answer

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.E) A) and D)
F) B) and C)

Question 4

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

Accepted Answer

A)  30,000
B)  2 x 106
C)  6 x 109
D)  6 x 1013E) None of the above
F) B) and C)

Question 5

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?

Accepted Answer

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

Question 6

The hydrogen Balmer H  α\alphaα  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?

Accepted Answer

A)  0.8c toward us
B)  0.8c away from us
C)  1.2c toward us
D)  1.2c away from us E) None of the above
F) A) and C)

Question 7

What is the lifetime of the average quasar?

Accepted Answer

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

Question 8

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

Accepted Answer

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.E) A) and B)
F) C) and D)

Question 9

To what does the phrase "superluminal motion" refer?

Accepted Answer

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 > 1E) All of the above
F) B) and C)

Question 10

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

Accepted Answer

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.E) A) and C)
F) None of the above

Question 11

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

Accepted Answer

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

Question 12

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

Accepted Answer

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.E) B) and D)
F) B) and C)

Question 13

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

Accepted Answer

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.E) All of the above
F) A) and B)

Question 14

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

Accepted Answer

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.E) None of the above
F) A) and D)

Question 15

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

Accepted Answer

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 sourceE) None of the above
F) All of the above

Question 16

Seyfert galaxies are:

Accepted Answer

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.E) None of the above
F) All of the above

Question 17

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

Accepted Answer

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.E) A) and D)
F) B) and C)

Question 18

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

Accepted Answer

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

Question 19

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:

Accepted Answer

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.E) C) and D)
F) A) and D)

Question 20

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

Accepted Answer

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.E) A) and B)
F) None of the above

Exam 24: Quasars and Active Galaxies

The hydrogen Balmer H α\alphaα 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?

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

To what does the phrase "superluminal motion" refer?

Correct AnswerverifiedShow Answer

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:

Correct AnswerverifiedShow Answer

How do we determine the distance to a quasar?

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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?

Correct AnswerverifiedShow Answer

What is the lifetime of the average quasar?

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

A radio galaxy is any galaxy that:

Correct AnswerverifiedShow Answer

Seyfert galaxies are:

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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?

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

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

Correct Answer
verified

Correct Answer
verified

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

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

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) ?

Correct Answer
verified

Correct Answer
verified