Deck 24: Quasars and Other Active Galaxies

Question 1

Which of the following is a good description of a Seyfert galaxy?

A)A spiral with a small bright nucleus
B)A giant elliptical
C)A tidally distorted irregular galaxy
D)A galaxy in which star formation has ceased

Answer 1

A spiral with a small bright nucleus

Question 2

How do we know that quasars are no larger than the solar system?

A)They vary in brightness on a timescale of days or weeks
B)They appear pointlike when viewed through a telescope
C)They contain black holes,which must be small
D)They are too luminous to be very large

Answer 2

They vary in brightness on a timescale of days or weeks

Question 3

Since quasars are thought to be at cosmological distances,we see them as they were when the universe was

A)Much older than it is today
B)Relatively young
C)Contracting
D)Much larger than it is today

Answer 3

Relatively young

Question 4

About how large is a 1 million solar mass black hole such as those that may exist at the centers of many galaxies?

A)A few km in radius
B)A few thousand km in radius
C)A few million km in radius
D)A few billion km in radius

Question 5

Some quasars vary in brightness in only a few days.What does this tell us about the quasars?

A)They have large magnetic fields
B)They are quite small
C)They must be highly luminous
D)They cannot emit radio waves

Question 6

Why do Seyfert Galaxies strengthen the case for quasars being active young galaxies?

A)Seyfert galaxies are closer than most quasars,and brighter.
B)Seyfert galaxies are closer than most quasars,and are less bright.
C)Seyfert galaxies are farther away than quasars,and are less bright.
D)Seyfert galaxies are father away than quasars,and are more bright.

Question 7

Quasars are currently believed to be

A)The brightest elliptical galaxies
B)The most luminous supernova remnants
C)An early phase of intense activity in the centers of galaxies
D)Structures larger than clusters of galaxies

Question 8

Quasars were originally discovered as

A)Strong radio sources identified with star-like images on photographs
B)Variable sources of light
C)Bright galaxies,and only later found to be radio sources
D)The only type of radio source within our galaxy

Question 9

Which of the following is true of Seyfert galaxies?

A)They have no spiral arms
B)They have unusually bright nuclei
C)They are a form of elliptical galaxy
D)They are all found in the Local Group of galaxies

Question 10

Quasars all have great distances.Why are there no nearby quasars?

A)No quasars have existed in the recent past
B)Quasars avoid spiral galaxies
C)Quasars are found only in clusters of galaxies
D)If quasars are too close to us,they look like pulsars

Question 11

How do we know that the quasars are at large distances?

A)They are extremely dim
B)They have large redshifts
C)They have large parallaxes
D)They are greatly obscured by interstellar dust

Question 12

For a typical luminous radio galaxy,most of the radio emission comes primarily from

A)The core of the galaxy
B)Spiral arms.
C)Globular clusters.
D)Two large regions far from the center of the galaxy

Question 13

Why was it difficult for astronomers to identify the spectral lines observed in the spectra of quasars?

A)They were formed by elements unknown on Earth
B)There were too many lines in the spectra
C)The lines were greatly redshifted
D)No two quasars have the same spectral lines

Question 14

How do astronomers explain the "superluminal" motions observed in quasars?

A)It is an illusion produced when something moves rapidly almost straight at us
B)No trick,things really do move faster than the speed of light
C)The black holes in quasars cause a distortion in the rate of passage of time
D)Quasars are contracting at almost the speed of light

Question 15

It is thought that most large galaxies probably have black holes at their centers.

Question 16

The spectra of quasars reveal lines of elements such as nitrogen and carbon.These elements are as abundant in quasars as in the Sun.Which of the following is a correct reflection on this fact?

A)This is to be expected,since quasars are powered by nucleosynthesis
B)This observation verifies our ideas on the evolutionary status of quasars
C)This is odd,since quasars are old and should have Pop.II abundances
D)This is unexpected,quasars should have large amounts of iron

Question 17

The radio emission from radio galaxies and quasars is due to

A)Thermal emission
B)21 cm radiation from hydrogen atoms.
C)Star formation regions.
D)Synchrotron radiation

Question 18

According to current theories,the energy source of radio galaxies and quasars is

A)A one thousand solar mass pulsar in each of two radio lobes
B)A one hundred million solar mass black hole at the center of the object
C)The conversion of hydrogen to helium via nuclear reactions
D)Gravitational contraction of massive stars near the spiral arms

Question 19

Absorption lines in quasars usually have lower redshifts than the quasars themselves do.This suggests that the absorption lines are caused by gas

A)At the same distance as the quasars
B)Between us and the quasars
C)That is farther away than the quasars
D)In the quasar itself