Question 1

Giant molecular clouds of H2 and CO gas are found in which regions of our galaxy?

Accepted Answer

A) They appear to be uniformly spread throughout the galaxy, both in the spiral arms and above and below them. 
B) They appear above and below the plane of the spiral arms, over the galactic poles. 
C) They are found at the center of the galaxy. 
D) They appear along the spiral arms. 
A) They appear to be uniformly spread throughout the galaxy, both in the spiral arms and above and below them. 
B) They appear above and below the plane of the spiral arms, over the galactic poles. 
C) They are found at the center of the galaxy. 
D) They appear along the spiral arms.

Question 2

What prevents a star from having a mass greater than about 200 M ? ?

Accepted Answer

A) No interstellar clouds are found that contain more than 200 M ? . 
B) A star of larger mass would collapse under its own gravity, and the whole star would become a black hole. 
C) Gas pressure becomes so high as a consequence of high temperatures that the excess mass is pushed back into space. 
D) The core of a larger-mass star would evolve rapidly and explode before the overall star finished contracting as a protostar. 
A) No interstellar clouds are found that contain more than 200 M ? . 
B) A star of larger mass would collapse under its own gravity, and the whole star would become a black hole. 
C) Gas pressure becomes so high as a consequence of high temperatures that the excess mass is pushed back into space. 
D) The core of a larger-mass star would evolve rapidly and explode before the overall star finished contracting as a protostar.

Question 3

A cocoon nebula is a:

Accepted Answer

A) bright knot of ionized gas in the bipolar outflow from a young star. 
B) cloud of dust hiding a young protostar from sight. 
C) giant molecular cloud containing young pre-stellar objects. 
D) dark globule of dust and gas silhouetted against a bright H II region. 
A) bright knot of ionized gas in the bipolar outflow from a young star. 
B) cloud of dust hiding a young protostar from sight. 
C) giant molecular cloud containing young pre-stellar objects. 
D) dark globule of dust and gas silhouetted against a bright H II region.

Question 4

In the magnetic model for the bipolar outflow from a protostar:

Accepted Answer

A) magnetic field lines emanate from the poles of the protostar and carry material outward from the stellar interior. 
B) magnetic field lines through the circumstellar accretion disk become twisted and concentrated by the rotation of this disk. 
C) magnetic field lines associated with the galaxy as a whole are concentrated and shaped by their interaction with the magnetosphere of the protostar. 
D) the jets are formed along magnetic field lines, which go from the north magnetic pole of one protostar to the south magnetic pole of a second protostar that forms a close binary pair with the first. 
A) magnetic field lines emanate from the poles of the protostar and carry material outward from the stellar interior. 
B) magnetic field lines through the circumstellar accretion disk become twisted and concentrated by the rotation of this disk. 
C) magnetic field lines associated with the galaxy as a whole are concentrated and shaped by their interaction with the magnetosphere of the protostar. 
D) the jets are formed along magnetic field lines, which go from the north magnetic pole of one protostar to the south magnetic pole of a second protostar that forms a close binary pair with the first.

Question 5

In the Hertzsprung-Russell diagram, how does the position of a typical star change while it is at the main-sequence phase of its evolution?

Accepted Answer

A) Stars move from upper right to lower left along the main sequence. 
B) A star moves very little on the H-R diagram while it is at this phase of its life. 
C) Massive stars ( > 4 M ? ) move toward the upper left as their luminosity increases, whereas lower-mass stars move toward the lower right as their temperature decreases along the main sequence. 
D) Stars move from upper left to lower right along the main sequence. 
A) Stars move from upper right to lower left along the main sequence. 
B) A star moves very little on the H-R diagram while it is at this phase of its life. 
C) Massive stars ( > 4 M ? ) move toward the upper left as their luminosity increases, whereas lower-mass stars move toward the lower right as their temperature decreases along the main sequence. 
D) Stars move from upper left to lower right along the main sequence.

Question 6

The average density in a dark nebula is about how many times the average density in the interstellar medium?

Accepted Answer

A) 10 
B) 1000 
C) 100,000 
D) 10 million 
A) 10 
B) 1000 
C) 100,000 
D) 10 million

Question 7

Where would you look to find a newly forming star?

Accepted Answer

A) a globular cluster 
B) an open cluster 
C) a planetary nebula 
D) inside a black hole 
A) a globular cluster 
B) an open cluster 
C) a planetary nebula 
D) inside a black hole

Question 8

Hydrogen atoms can be ionized by light with a wavelength of 9.12 × 10-8 m or shorter. What approximate temperature would a star need in order to have the PEAK of its spectrum at this wavelength?

Accepted Answer

A) 32,000 K 
B) 44,000 K 
C) 51 million K 
D) 4 × 1015 K 
A) 32,000 K 
B) 44,000 K 
C) 51 million K 
D) 4 × 1015 K

Question 9

The effect of interstellar dust on starlight is:

Accepted Answer

A) to dim and redden distant stars by preferentially scattering their blue light. 
B) to scatter the red light from stars preferentially, making them appear more blue than expected. 
C) almost nonexistent, because light does not interact with dust. 
D) to make stars appear less bright than expected by absorbing light about equally at all wavelengths. 
A) to dim and redden distant stars by preferentially scattering their blue light. 
B) to scatter the red light from stars preferentially, making them appear more blue than expected. 
C) almost nonexistent, because light does not interact with dust. 
D) to make stars appear less bright than expected by absorbing light about equally at all wavelengths.

Question 10

What is the ultimate fate of an open cluster (or galactic cluster) of stars?

Accepted Answer

A) It is torn apart by collisions with giant molecular clouds. 
B) Its stars finish their lives and explode as supernovae, until eventually there are no stars left. 
C) It gradually becomes more compact until the stars in it merge and collapse to become a supermassive black hole. 
D) Its stars escape one by one until the cluster no longer exists. 
A) It is torn apart by collisions with giant molecular clouds. 
B) Its stars finish their lives and explode as supernovae, until eventually there are no stars left. 
C) It gradually becomes more compact until the stars in it merge and collapse to become a supermassive black hole. 
D) Its stars escape one by one until the cluster no longer exists.

Question 11

We see an emission nebula predominantly in:

Accepted Answer

A) blue light, originally emitted by stars within the nebula but scattered by dust. 
B) light emitted over a wide range of wavelengths by dust grains that have been heated by radiation from embedded stars. 
C) light emitted by molecules in the dense clouds of gas surrounding the stars in the nebula. 
D) the Balmer Hα red line, from recombination of electrons with nuclei in ionized hydrogen. 
A) blue light, originally emitted by stars within the nebula but scattered by dust. 
B) light emitted over a wide range of wavelengths by dust grains that have been heated by radiation from embedded stars. 
C) light emitted by molecules in the dense clouds of gas surrounding the stars in the nebula. 
D) the Balmer Hα red line, from recombination of electrons with nuclei in ionized hydrogen.

Question 12

What is the lowest mass that an object can have and still be a star?

Accepted Answer

A) 0.08 M ? (80 times Jupiter's mass) 
B) 0.02 M ? (20 times Jupiter's mass) 
C) 0.002 M ? (twice Jupiter's mass) 
D) 0.80 M ? (800 times Jupiter's mass) 
A) 0.08 M ? (80 times Jupiter's mass) 
B) 0.02 M ? (20 times Jupiter's mass) 
C) 0.002 M ? (twice Jupiter's mass) 
D) 0.80 M ? (800 times Jupiter's mass)

Question 13

Which of the following trigger mechanisms for the initiation of stellar formation in gas and dust clouds produces many high-mass O and B stars but only a few low-mass stars?

Accepted Answer

A) passage of the cloud through a black hole 
B) compression caused by the passage of the cloud through a galactic spiral arm 
C) shock waves from a supernova explosion 
D) gravitational condensation of the cloud 
A) passage of the cloud through a black hole 
B) compression caused by the passage of the cloud through a galactic spiral arm 
C) shock waves from a supernova explosion 
D) gravitational condensation of the cloud

Question 14

Herbig-Haro objects are:

Accepted Answer

A) dense dust clouds surrounding and being heated by massive protostars. 
B) higher density knots of matter in protoplanetary disks around very young, low-mass stars. 
C) regions of ionized gas on the edges of giant molecular clouds. 
D) luminous knots of material at either end of bipolar jets emerging from young T Tauri stars. 
A) dense dust clouds surrounding and being heated by massive protostars. 
B) higher density knots of matter in protoplanetary disks around very young, low-mass stars. 
C) regions of ionized gas on the edges of giant molecular clouds. 
D) luminous knots of material at either end of bipolar jets emerging from young T Tauri stars.

Question 15

The Hubble Space Telescope has photographed disks of gas and dust around young, low-mass stars in the Orion Nebula. It is thought that planets may form from the material in disks such as these. What name has been given to these disks?

Accepted Answer

A) stellar accretions 
B) proplyds 
C) cocoon nebulae 
D) Barnard objects 
A) stellar accretions 
B) proplyds 
C) cocoon nebulae 
D) Barnard objects

Question 16

The most abundant material in a giant molecular cloud is:

Accepted Answer

A) carbon monoxide. 
B) hydrogen. 
C) dust. 
D) water vapor. 
A) carbon monoxide. 
B) hydrogen. 
C) dust. 
D) water vapor.

Question 17

What is believed to be the maximum mass that a star can have?

Accepted Answer

A) There appears to be no physical limit. 
B) about 1000 M ? 
C) about 200 M ? 
D) about 5 M ? 
A) There appears to be no physical limit. 
B) about 1000 M ? 
C) about 200 M ? 
D) about 5 M ?

Question 18

A particular, dense interstellar cloud is about 10 pc (30 ly) across and contains a few thousand M ? of material. This cloud is classified as a:

Accepted Answer

A) Barnard object. 
B) Herbig-Haro object. 
C) bipolar outflow. 
D) giant molecular cloud. 
A) Barnard object. 
B) Herbig-Haro object. 
C) bipolar outflow. 
D) giant molecular cloud.

Question 19

What is the mass of a typical giant molecular cloud?

Accepted Answer

A) 10 to 200 M ? 
B) 1000 to 20,000 M ? 
C) 100,000 to 2 million M ? 
D) 10 million to 2 billion M ? 
A) 10 to 200 M ? 
B) 1000 to 20,000 M ? 
C) 100,000 to 2 million M ? 
D) 10 million to 2 billion M ?

Question 20

Long-exposure color photographs of the night sky often show regions that glow red, such as parts of the Orion Nebula. This distinctive red color is caused by:

Accepted Answer

A) ionization and subsequent recombination of hydrogen atoms. 
B) the emission of red and infrared light by warm dust grains. 
C) the collective glow of many red giant stars in the region. 
D) scattering of starlight by dust grains in the nebula. 
A) ionization and subsequent recombination of hydrogen atoms. 
B) the emission of red and infrared light by warm dust grains. 
C) the collective glow of many red giant stars in the region. 
D) scattering of starlight by dust grains in the nebula.

Exam 18: The Birth of Stars

Giant molecular clouds of H2 and CO gas are found in which regions of our galaxy?

What prevents a star from having a mass greater than about 200 M ? ?

A cocoon nebula is a:

In the magnetic model for the bipolar outflow from a protostar:

In the Hertzsprung-Russell diagram, how does the position of a typical star change while it is at the main-sequence phase of its evolution?

The average density in a dark nebula is about how many times the average density in the interstellar medium?

Where would you look to find a newly forming star?

Hydrogen atoms can be ionized by light with a wavelength of 9.12 × 10-8 m or shorter. What approximate temperature would a star need in order to have the PEAK of its spectrum at this wavelength?

The effect of interstellar dust on starlight is:

What is the ultimate fate of an open cluster (or galactic cluster) of stars?

We see an emission nebula predominantly in:

What is the lowest mass that an object can have and still be a star?

Which of the following trigger mechanisms for the initiation of stellar formation in gas and dust clouds produces many high-mass O and B stars but only a few low-mass stars?

Herbig-Haro objects are:

The Hubble Space Telescope has photographed disks of gas and dust around young, low-mass stars in the Orion Nebula. It is thought that planets may form from the material in disks such as these. What name has been given to these disks?

The most abundant material in a giant molecular cloud is:

What is believed to be the maximum mass that a star can have?

A particular, dense interstellar cloud is about 10 pc (30 ly) across and contains a few thousand M ? of material. This cloud is classified as a:

What is the mass of a typical giant molecular cloud?

Long-exposure color photographs of the night sky often show regions that glow red, such as parts of the Orion Nebula. This distinctive red color is caused by:

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

Filters

Giant molecular clouds of H₂ and CO gas are found in which regions of our galaxy?

Hydrogen atoms can be ionized by light with a wavelength of 9.12 × 10^-8 m or shorter. What approximate temperature would a star need in order to have the PEAK of its spectrum at this wavelength?