Exam 2 Key

Multiple Choice

Identify the choice that best completes the statement or answers the question.

1. What happens during the planetary nebula stage in the lifetime of a star with a mass similar to that of our Sun?

a.	The envelope of the star rapidly forms compact spherical objects – planets.
b.	The envelope of the star deforms from a spherical to a disk-like shape as a result of the star’s increasing rate of rotation.
c.	The envelope of the star separates from the inert and degenerate core and drifts away.
d.	The envelope of the star violently collapses onto the inert and degenerate core of the star.
e.	The envelope rapidly changes its chemical composition from mostly hydrogen and helium gas to iron and nickel granules.

2. Which four adjectives would apply to a white dwarf?

a.	Luminous, small, hot, non-degenerate
b.	Luminous, large, hot, non-degenerate
c.	Dim, large, cool, degenerate
d.	Dim, small, cool, non-degenerate
e.	Dim, small, hot, degenerate

3. When the core of a high mass star is composed of this element, the star becomes unstable and explodes as a supernova. What element is it?

a.	Uranium
b.	Iron
c.	Xenon
d.	Silicon
e.	Helium

4. Which observation suggests that the Milky Way is a disk galaxy?

a.	The stars of the Milky Way have about 2% abundance of heavy elements.
b.	Astronomers have detected a million solar mass black hole in the center of the Milky Way.
c.	The light of the Milky Way appears as a luminous band stretching across the sky.
d.	There are hundreds of globular clusters containing old, metal-poor stars in the Milky Way.
e.	The majority of stars have a gaseous disk around them.

5. Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit (i.e., the Chandrasekhar limit)?

a.	The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star, but is comparable in energy.
b.	The white dwarf, which is made mostly of carbon, suddenly becomes much hotter and is therefore able to begin fusing carbon. This turns the white dwarf back into a star supported against gravity by ordinary pressure.
c.	The white dwarf immediately collapses into a black hole, disappearing from view.
d.	The white dwarf “freezes out” and becomes a black dwarf.
e.	A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the material from reaching it in the first place.

6. What is Hubble’s law?

a.	The longer the time period between peaks in brightness, the greater the luminosity of the Cepheid variable star.
b.	The recession velocity of a galaxy is inversely proportional to its distance from us.
c.	The recession velocity of a galaxy is directly proportional to its distance from us.
d.	The faster a spiral galaxy’s rotation speed, the less luminous it is.
e.	None of the above.

7. One primary difference between spiral and elliptical galaxies is:

a.	All elliptical galaxies are more massive than spiral galaxies.
b.	Elliptical galaxies contain less interstellar medium than do spiral galaxies.
c.	Star formation is more common in elliptical galaxies than in spiral galaxies.
d.	Spiral galaxies have more stars than do elliptical galaxies.
e.	Elliptical galaxies can have bars, but spiral galaxies cannot.

8. Why is a galaxy much more likely to collide with another galaxy than a star is to collide with another star?

a.	Sizes of galaxies are of appreciable fraction compared to their separations. This is not true for stars.
b.	Sizes of galaxies are of negligible fraction compared to their separations. This is not true for stars.
c.	Galaxies attract each other by their strong nuclear forces; stars do not.
d.	Galaxies attract each other by their strong magnetic forces; stars do not.
e.	Galaxies attract each other by their strong electric forces; stars do not.

9. Surveys of galaxies reveal that:

a.	Our Galaxy is at the center of the Universe.
b.	Galaxies and galaxy clusters are randomly distributed in the Universe.
c.	Galaxies and galaxy clusters are not randomly distributed in the Universe. Instead, they tend to form structures such as “walls” or “sheets,” surrounding regions of relative emptiness – “voids.”
d.	Galaxies and galaxy clusters are no more distant than 100 Mpc. Beyond 100 Mpc, the universe is devoid of galaxies.
e.	Our Galaxy is the only real galaxy in the Universe. The other galaxies are merely gravitational lenses of our Galaxy.

10. Which of the following statements best describes the location of the Sun in the Milky Way?

a.	The Sun is located at the center of the Milky Way.
b.	The Sun is located in the Galactic disk and about 8 – 8.5 kpc from the Galactic center.
c.	The Sun is located at the edge of the Galactic disk.
d.	The Sun is located in the Galactic halo and about 15 kpc from the Galactic center.
e.	The Sun is located in the Galactic bulge and about 1 kpc from the Galactic center.

11. A galaxy is a system of stars, dark matter, gas, and dust. What force keeps these objects together as a system?

a.	Friction between matter and space
b.	Nuclear force
c.	Magnetic force
d.	Gravitational force
e.	Electric force

12. Which statement best describes the motion of the Sun in the Milky Way?

a.	The Sun is stationary at the center of the Milky Way.
b.	The Sun revolves around the center of the Milky Way on an approximately circular orbit of 8.5-kpc radius that is perpendicular to the Milky Way’s disk and with the speed of about 220 km/s.
c.	The Sun moves randomly throughout the Milky Way’s space, spending most of the time in the halo.
d.	The Sun revolves around the center of the Milky Way on an approximately circular orbit of 8.5-kpc radius located in the Milky Way’s disk and with the speed of about 220 km/s.
e.	The Sun moves directly away from the center of the Milky Way with a constant speed of about 400 km/s.

13. In the Theory of General Relativity, gravity is the manifestation of:

a.	Rigidity of the space-time
b.	Curvature of the space-time
c.	Thickness of the space-time
d.	Electric charge of the space-time
e.	Porosity of the space-time

14. If our Sun were to become a black hole, it would have to be compressed to a sphere with the radius of about:

a.	3 centimeters
b.	3 meters
c.	300 meters
d.	3 kilometers
e.	300 kilometers

15. Mass transfer in binaries occurs when one star expands and fills the:

a.	Chandrasekhar Limit
b.	Cassini Division
c.	Hayashi Track
d.	Roche Lobe
e.	Herbig-Haro Limit

16. How does a black hole form from a massive star?

a.	During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.
b.	Under some conditions, the helium flash in a massive star leads to the formation of a black hole.
c.	If a massive star merges with a white dwarf, a black hole forms.
d.	If a massive star merges with a neutron star, a black hole forms.
e.	A black hole forms when two massive main-sequence stars collide.

17. Which of the following has a radius closest to that of a neutron star?

a.	The Sun
b.	The Earth
c.	A large city
d.	A basketball
e.	An atom

18. What is the Hubble classification of an elliptical galaxy that appears spherical in shape?

a.	S0
b.	G0
c.	SGO
d.	EG7
e.	E0

19. Which one of these objects emits Hawking radiation?

a.	Sun
b.	Neutron star
c.	White dwarf
d.	Black hole
e.	Cepheid variable

20. Astronomers have convincing evidence that this object with a mass of about million Suns resides at the center of the Milky Way? What object is it?

a.	Pulsar
b.	UFO
c.	Quark hole
d.	White hole
e.	Black hole