Question 1

Herbig-Haro objects, bright, variable regions within nebulae, are now thought to be the result of:

Accepted Answer

A) the initial condensation of matter into a protostar, producing an infrared and visible glow. 
B) intense jets of material ejected from a young star, hitting parts of the nebula. 
C) brightening of the gas surrounding a massive star as the precursor to a supernova explosion. 
D) the hot atmosphere of a star as it is ejected in the dying phases of the star's life. 
A) the initial condensation of matter into a protostar, producing an infrared and visible glow. 
B) intense jets of material ejected from a young star, hitting parts of the nebula. 
C) brightening of the gas surrounding a massive star as the precursor to a supernova explosion. 
D) the hot atmosphere of a star as it is ejected in the dying phases of the star's life.

Question 2

Which of the following is a tightly bound physical system, likely to endure for many billions of years?

Accepted Answer

A) a binary star system 
B) an open cluster 
C) a stellar association 
D) an OB association 
A) a binary star system 
B) an open cluster 
C) a stellar association 
D) an OB association

Question 3

Evidence for the interstellar medium has been provided by all of the following EXCEPT ONE. Which is the EXCEPTION?

Accepted Answer

A) the existence of interstellar clouds like the Horsehead Nebula in Orion 
B) unshifted spectral lines observed when examining a binary star system 
C) interstellar reddening 
D) the neutrino flux 
A) the existence of interstellar clouds like the Horsehead Nebula in Orion 
B) unshifted spectral lines observed when examining a binary star system 
C) interstellar reddening 
D) the neutrino flux

Question 4

A T Tauri star is:

Accepted Answer

A) an intermediate mass protostar near the end of its pre-main-sequence lifetime. 
B) a young, massive O or B star. 
C) a low-mass protostar embedded in a cocoon of dust clouds. 
D) a high-mass protostar surrounded by a rotationally flattened disk of gas and dust. 
A) an intermediate mass protostar near the end of its pre-main-sequence lifetime. 
B) a young, massive O or B star. 
C) a low-mass protostar embedded in a cocoon of dust clouds. 
D) a high-mass protostar surrounded by a rotationally flattened disk of gas and dust.

Question 5

The smallest mass that a main-sequence star can have is about 0.08 M ? . The reason for this is that:

Accepted Answer

A) the temperature in the core of a contracting protostar of less than 0.08 M ? does not get high enough for nuclear reactions to start. 
B) protostars cannot form with masses less than 0.08 M ? 
C) thermonuclear reactions begin so suddenly in stars of less than 0.08 M ? that the star is disrupted by an explosion. 
D) protostars of less than 0.08 M ? are not massive enough to contract. 
A) the temperature in the core of a contracting protostar of less than 0.08 M ? does not get high enough for nuclear reactions to start. 
B) protostars cannot form with masses less than 0.08 M ? 
C) thermonuclear reactions begin so suddenly in stars of less than 0.08 M ? that the star is disrupted by an explosion. 
D) protostars of less than 0.08 M ? are not massive enough to contract.

Question 6

How large and bright is a young protostar of 1 M ? , whose age is about 1000 years, compared to the radius R and luminosity L of the Sun?

Accepted Answer

A) 1 × R, the same size as the Sun, and 100 × L 
B) 20 × R, 100 × L 
C) 1 × R, 1 × L, because a protostar of this mass has already evolved to a Sun-like main-sequence star 
D) 20 × R, but still much fainter than the Sun, at L/10 
A) 1 × R, the same size as the Sun, and 100 × L 
B) 20 × R, 100 × L 
C) 1 × R, 1 × L, because a protostar of this mass has already evolved to a Sun-like main-sequence star 
D) 20 × R, but still much fainter than the Sun, at L/10

Question 7

A large emission nebula contains about how many solar masses of material?

Accepted Answer

A) 1 
B) 100 
C) 10,000 
D) 1 million 
A) 1 
B) 100 
C) 10,000 
D) 1 million

Question 8

Protostars with masses of more than about 4 times the mass of the Sun maintain approximately constant luminosity through their pre-main-sequence lifetimes. This is because:

Accepted Answer

A) the star contracts as its surface temperature decreases, and the change in surface area compensates for the change in energy emitted per unit area. 
B) the surface temperature increases as the star contracts, and the change in energy emitted per unit area compensates for the change in surface area. 
C) they contract too rapidly for their temperature and luminosity to change significantly. 
D) they are too massive to contract significantly, thus keeping luminosity constant. 
A) the star contracts as its surface temperature decreases, and the change in surface area compensates for the change in energy emitted per unit area. 
B) the surface temperature increases as the star contracts, and the change in energy emitted per unit area compensates for the change in surface area. 
C) they contract too rapidly for their temperature and luminosity to change significantly. 
D) they are too massive to contract significantly, thus keeping luminosity constant.

Question 9

How large was the Sun when it first formed as a protostar, perhaps 1000 years after formation?

Accepted Answer

A) the same diameter as it is now 
B) about 100 times its present diameter 
C) about 1000 times its present diameter 
D) about 20 times its present diameter 
A) the same diameter as it is now 
B) about 100 times its present diameter 
C) about 1000 times its present diameter 
D) about 20 times its present diameter

Question 10

A star-forming region is best viewed in what region of the electromagnetic spectrum?

Accepted Answer

A) visible 
B) ultraviolet 
C) infrared 
D) radio 
A) visible 
B) ultraviolet 
C) infrared 
D) radio

Question 11

The expanding shell of gas from a supernova has the ability to compress the medium through which it is moving abruptly enough to trigger star formation. What special characteristic of this expanding shell allows it to do this?

Accepted Answer

A) It is accompanied by a flood of ultraviolet radiation. 
B) It is supersonic. 
C) It is pure hydrogen. 
D) It contains heavy elements that can only be produced in supernovae. 
A) It is accompanied by a flood of ultraviolet radiation. 
B) It is supersonic. 
C) It is pure hydrogen. 
D) It contains heavy elements that can only be produced in supernovae.

Question 12

T Tauri stars are at what stage of stellar evolution?

Accepted Answer

A) early phase, just after the formation of the protostar 
B) just after the red giant phase 
C) post-main sequence or later phase 
D) main sequence or "middle age" 
A) early phase, just after the formation of the protostar 
B) just after the red giant phase 
C) post-main sequence or later phase 
D) main sequence or "middle age"

Question 13

At approximately what temperature will nuclear reactions begin in the core of a pre-main-sequence star?

Accepted Answer

A) 50 million K 
B) 1 million K 
C) 500,000 K 
D) 5 million K 
A) 50 million K 
B) 1 million K 
C) 500,000 K 
D) 5 million K

Question 14

Giant molecular clouds, which are major sites of star formation, can be up to:

Accepted Answer

A) 1000 pc across and contain 100 million M ? of material. 
B) 10 times the size of the solar system and contain 2 to 3 M ? of material. 
C) 100 pc across and contain 2 million M ? of material. 
D) 10 pc across and contain a few thousand M ? of material. 
A) 1000 pc across and contain 100 million M ? of material. 
B) 10 times the size of the solar system and contain 2 to 3 M ? of material. 
C) 100 pc across and contain 2 million M ? of material. 
D) 10 pc across and contain a few thousand M ? of material.

Question 15

Modern astronomers have been observing stars for about a century. What fraction is this of the typical lifetime of a normal main sequence?

Accepted Answer

A) 1 part in 1010 
B) 1 part in 1012 
C) 1 part in 105 
D) 1 part in 108 
A) 1 part in 1010 
B) 1 part in 1012 
C) 1 part in 105 
D) 1 part in 108

Question 16

How does a massive star normally end its life?

Accepted Answer

A) It gradually shrinks to the size of Earth. 
B) We don't know, because its lifetime is longer than the age of the universe. 
C) It collapses inward, and the whole star becomes a black hole. 
D) It explodes. 
A) It gradually shrinks to the size of Earth. 
B) We don't know, because its lifetime is longer than the age of the universe. 
C) It collapses inward, and the whole star becomes a black hole. 
D) It explodes.

Question 17

A Herbig-Haro object is:

Accepted Answer

A) the gas cloud produced by a supernova explosion. 
B) a dark nebula that obscures distant stars from our view. 
C) a young protostar emerging from its nebula. 
D) glowing interstellar gas, heated by a high-velocity jet of matter from an evolving star. 
A) the gas cloud produced by a supernova explosion. 
B) a dark nebula that obscures distant stars from our view. 
C) a young protostar emerging from its nebula. 
D) glowing interstellar gas, heated by a high-velocity jet of matter from an evolving star.

Exam 18: The Birth of Stars

Herbig-Haro objects, bright, variable regions within nebulae, are now thought to be the result of:

Which of the following is a tightly bound physical system, likely to endure for many billions of years?

Evidence for the interstellar medium has been provided by all of the following EXCEPT ONE. Which is the EXCEPTION?

A T Tauri star is:

The smallest mass that a main-sequence star can have is about 0.08 M ? . The reason for this is that:

How large and bright is a young protostar of 1 M ? , whose age is about 1000 years, compared to the radius R and luminosity L of the Sun?

A large emission nebula contains about how many solar masses of material?

Protostars with masses of more than about 4 times the mass of the Sun maintain approximately constant luminosity through their pre-main-sequence lifetimes. This is because:

How large was the Sun when it first formed as a protostar, perhaps 1000 years after formation?

A star-forming region is best viewed in what region of the electromagnetic spectrum?

The expanding shell of gas from a supernova has the ability to compress the medium through which it is moving abruptly enough to trigger star formation. What special characteristic of this expanding shell allows it to do this?

T Tauri stars are at what stage of stellar evolution?

At approximately what temperature will nuclear reactions begin in the core of a pre-main-sequence star?

Giant molecular clouds, which are major sites of star formation, can be up to:

Modern astronomers have been observing stars for about a century. What fraction is this of the typical lifetime of a normal main sequence?

How does a massive star normally end its life?

A Herbig-Haro object is:

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Optics and Telescopes

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

Stellar Evolution: on and After the Main Sequence

Stellar Evolution: The Death of Stars

Stellar Remnants: Neutron Stars and Black Holes

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

Exploring the Early Universe

The Search for Extraterrestrial Life

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