Question 1

An electron moving in a magnetic field in space is forced to move in a spiral pattern.As it does so,it emits:

Accepted Answer

A)   characteristic X rays as the electron is slowed down by this motion.
B)   visible light, mostly blue in color because the electron is forced to move in a circular path.
C)   synchrotron radiation, mostly radio waves, since the electrons are accelerating.
D)   nothing since such electrons are moving with a constant speed and are not therefore accelerating.E) None of the above
F) All of the above

Question 2

The Milky Way Galaxy and the Andromeda Galaxy (M31) will probably collide in about four billion years.What is the probable result?

Accepted Answer

A)   Both galaxies will disappear and become part of the intergalactic medium.
B)   A larger spiral will form.
C)   A giant elliptical will form.
D)   An irregular galaxy will form.E) None of the above
F) B) and C)

Question 3

A starlike object seen on deep sky photographs coincides with an intense radio source and has a spectrum in which the characteristic Lyman pattern of hydrogen spectral lines has been shifted from the ultraviolet to the visible spectral range.What is this object?

Accepted Answer

A)   a quasar
B)   a pulsar
C)   a supernova explosion
D)   a black holeE) All of the above
F) B) and C)

Question 4

Which type of radiation has been MOST effective in evaluating the spiral arm structure of our Galaxy?

Accepted Answer

A)   21-cm radio emission from electron "spin-flip" transitions in cool hydrogen gas
B)   Lyman-α ultraviolet emission from hot hydrogen gas
C)   synchrotron radiation from electrons spiraling in magnetic fields in the spiral arms
D)   neutrinos from exploding stars in the spiral arms since they can easily penetrate dust and gasE) None of the above
F) A) and C)

Question 5

If most of the mass of a galaxy is located near the center of the galaxy,then in the outer part of this galaxy we would expect the orbital speeds of stars to decrease with increasing distance from the center.This behavior would be equivalent to:

Accepted Answer

A)   Newton's third law.
B)   Wien's law.
C)   Hubble's law.
D)   Kepler's third law.E) All of the above
F) C) and D)

Question 6

For which object has the phenomenon of differential rotation NOT been observed?

Accepted Answer

A)   Mars
B)   Jupiter
C)   the Sun
D)   the Milky Way GalaxyE) A) and C)
F) B) and D)

Question 7

In which type of galaxy is star formation no longer occurring?

Accepted Answer

A)   irregular
B)   barred spiral
C)   spiral
D)   ellipticalE) B) and C)
F) A) and D)

Question 8

Why is it strange to find spiral arms in spiral galaxies (see Figure 13-24,Comins,Discovering the Essential Universe,6th ed.) ?

Accepted Answer

A)   Spiral arms require new stars, and previous new stars should have already used up the interstellar medium; no new stars should be forming now.
B)   The variations in speed of the stars across galaxies are not high enough to twist the shape of the arms into a spiral.
C)   There is no known mechanism to generate spiral arms.
D)   The motions of the stars and differential rotation of the galaxy should have wound their arms tightly and made them blend and disappear.E) B) and C)
F) A) and D)

Question 9

When a hydrogen atom is excited by some addition of energy and it responds with electron transitions between electron energy levels,the radiation it emits is usually in which regions of the electromagnetic spectrum?

Accepted Answer

A)   visible and infrared
B)   visible and ultraviolet
C)   radio
D)   microwaveE) B) and C)
F) C) and D)

Question 10

What is the distribution of stars in the spiral arms of a typical spiral galaxy?

Accepted Answer

A)   The density of stars in the arms is far higher than the density of stars between the arms.
B)   Far fewer but brighter stars exist in the arms, while many more fainter stars exist between the arms.
C)   All the stars of a spiral galaxy are in the arms; there are none at all between the arms.
D)   The density of stars is relatively uniform in the disk of the galaxy but is slightly higher within the arms than between them.E) B) and C)
F) A) and B)

Question 11

Why is the Milky Way Galaxy different from most spiral galaxies?

Accepted Answer

A)   The Milky Way has only three spiral arms, whereas most spiral galaxies have at least four.
B)   The Milky Way has only two spiral arms, whereas most galaxies have at least four.
C)   The spiral arms of the Milky Way are far more tightly wound than those in most galaxies.
D)   The Milky Way has at least four spiral arms, whereas most galaxies have only two.E) C) and D)
F) B) and D)

Question 12

An elliptical galaxy typically contains which kinds of stars?

Accepted Answer

A)   primarily young, metal-rich stars
B)   stars of all ages, but all metal-poor
C)   primarily old, metal-poor stars
D)   stars of all ages from young, metal-rich stars to old, metal-poor starsE) B) and C)
F) A) and D)

Question 13

The vast majority of the stars in the galactic halo are isolated field stars.What is the origin of these stars?

Accepted Answer

A)   These very old stars are left over from the original in-fall of the material that formed our galaxy.
B)   These are stars left over from the formation of the globular clusters.
C)   These are stars that were moving too fast and were expelled from globular clusters.
D)   These are the remnants of small galaxies that have been absorbed by the Milky Way Galaxy.E) B) and D)
F) B) and C)

Question 14

We find almost no quasars younger than about _____ billion years.

Accepted Answer

A)   7
B)   9
C)   11
D)   13E) A) and B)
F) None of the above

Question 15

The Tully-Fisher relationship can be used to measure the luminosity of (and thus the distance to) :

Accepted Answer

A)   elliptical galaxies.
B)   spiral galaxies.
C)   globular clusters.
D)   Type II supernovae.E) A) and C)
F) All of the above

Question 16

Elliptical galaxies look far less impressive than spiral galaxies because:

Accepted Answer

A)   they contain far fewer stars.
B)   there are none within our Local Group, so the only elliptical galaxies we see are at very large distances from us.
C)   they contain no gas and dust clouds or young, hot stars.
D)   they are always smaller.E) A) and C)
F) B) and D)

Question 17

At visible wavelengths,which galaxies are the brightest in the universe?

Accepted Answer

A)   giant elliptical
B)   lenticular
C)   large spiral, like the Milky Way
D)   starburstE) A) and B)
F) A) and C)

Question 18

Barred galaxies:

Accepted Answer

A)   are increasing in number as the universe ages.
B)   are mostly leading-arm spirals.
C)   all have tightly wound spiral arms.
D)   all have spiral arms wound with various degrees of tightness.E) A) and D)
F) All of the above

Question 19

The supermassive black hole at the center of our Milky Way Galaxy is believed to be 4.3 × 10⁶ solar masses.The nearest of the stars orbiting it has a period of 11.5 years.What is the semimajor axis of the orbit of this star (in AU) ?

Accepted Answer

A)   716
B)   828
C)   5090
D)   2.6 × 10⁷E) B) and C)
F) A) and D)

Question 20

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

Accepted Answer

A)   Quasars have incredible power as radio emitters, such that simple receivers can detect them from vast distances across the universe.
B)   Quasars have an energy output equivalent to more than 100 ordinary galaxies from a volume as small as our planetary system.
C)   The distance of quasars from the Sun is up to 18 billion ly.
D)   The recession velocities or quasars can be up to 9/10 of the speed of light.E) B) and C)
F) A) and D)

Exam 13: The Galaxies

Barred galaxies:

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

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Why is the Milky Way Galaxy different from most spiral galaxies?

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We find almost no quasars younger than about _____ billion years.

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Why is it strange to find spiral arms in spiral galaxies (see Figure 13-24,Comins,Discovering the Essential Universe,6th ed.) ?

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An elliptical galaxy typically contains which kinds of stars?

Correct AnswerverifiedShow Answer

The supermassive black hole at the center of our Milky Way Galaxy is believed to be 4.3 × 10⁶ solar masses.The nearest of the stars orbiting it has a period of 11.5 years.What is the semimajor axis of the orbit of this star (in AU) ?

Correct AnswerverifiedShow Answer

Elliptical galaxies look far less impressive than spiral galaxies because:

Correct AnswerverifiedShow Answer

The vast majority of the stars in the galactic halo are isolated field stars.What is the origin of these stars?

Correct AnswerverifiedShow Answer

A starlike object seen on deep sky photographs coincides with an intense radio source and has a spectrum in which the characteristic Lyman pattern of hydrogen spectral lines has been shifted from the ultraviolet to the visible spectral range.What is this object?

Correct AnswerverifiedShow Answer

An electron moving in a magnetic field in space is forced to move in a spiral pattern.As it does so,it emits:

Correct AnswerverifiedShow Answer

For which object has the phenomenon of differential rotation NOT been observed?

Correct AnswerverifiedShow Answer

The Milky Way Galaxy and the Andromeda Galaxy (M31) will probably collide in about four billion years.What is the probable result?

Correct AnswerverifiedShow Answer

The Tully-Fisher relationship can be used to measure the luminosity of (and thus the distance to) :

Correct AnswerverifiedShow Answer

When a hydrogen atom is excited by some addition of energy and it responds with electron transitions between electron energy levels,the radiation it emits is usually in which regions of the electromagnetic spectrum?

Correct AnswerverifiedShow Answer

Which type of radiation has been MOST effective in evaluating the spiral arm structure of our Galaxy?

Correct AnswerverifiedShow Answer

What is the distribution of stars in the spiral arms of a typical spiral galaxy?

Correct AnswerverifiedShow Answer

In which type of galaxy is star formation no longer occurring?

Correct AnswerverifiedShow Answer

If most of the mass of a galaxy is located near the center of the galaxy,then in the outer part of this galaxy we would expect the orbital speeds of stars to decrease with increasing distance from the center.This behavior would be equivalent to:

Correct AnswerverifiedShow Answer

At visible wavelengths,which galaxies are the brightest in the universe?

Correct AnswerverifiedShow Answer

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