ASTR 102 Chapter 16: Star Birth

Astronomers estimate that new stars form in our galaxy at the rate of about

A) one per year.

B) a few (2-3) per year.

C) ten per year.

D) 20-30 per year.

E) 100 per year.

B) a few (2-3) per year.

The typical density and temperature of molecular clouds are

A) 100 molecules per cubic centimeter, 10-30 Kelvin.

B) 300 molecules per cubic centimeter, 10-30 Kelvin.

C) 1000 molecules per cubic centimeter, 10-30 Kelvin.

D) 100 molecules per cubic centimeter, 100-300 Kelvin.

E) 300 molecules per cubic centimeter, 100-300 Kelvin.

B) 300 molecules per cubic centimeter, 10-30 Kelvin.

What is interstellar reddening?

A) Interstellar dust absorbs more red light than blue light, making stars appear redder than their true color.

B) Interstellar dust absorbs more red light than blue light, making stars appear bluer than their true color.

C) Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color.

D) Interstellar dust absorbs more blue light than red light, making stars appear bluer than their true color.

E) The spectral line shift due to a star's motion through the interstellar medium.

C) Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color.

If you wanted to observe a molecular cloud, in what wavelength of light would you most likely observe?

A) ultraviolet

B) visible

C) infrared

D) X-ray

E) gamma-ray

C) infrared

What happens to the visible radiation produced by new stars within a molecular cloud?

A) It escapes the cloud completely.

B) It is absorbed by dust grains and heats up the cloud.

C) It is reflected back onto the protostar, heating it up further.

D) The blue light is absorbed and the red light transmitted.

E) It shoots out in bright jets.

B) It is absorbed by dust grains and heats up the cloud.

What is the likely reason that we cannot find any examples of the first generation stars?

A) The first generation stars are too faint to be visible now.

B) The first generation stars formed such a long time ago that the light from them has not yet had time to reach us.

C) The first generation stars were all very massive and exploded as supernova.

D) The first generation stars formed with only H and He and therefore have no spectral features.

E) We do not know how the first generation stars were formed.

C) The first generation stars were all very massive and exploded as supernova.

What happens to the rotation of a molecular cloud as it collapses to form a star?

A) The rotation rate remains the same and results in stellar rotation.

B) The rotation dissipates and any residual is left in small overall rotation of the star.

C) The rotation rate increases and results in fast rotation of the star.

D) The rotation rate increases and results in a disk of material around a protostar.

E) The rotation increases the speed of collapse and produces more massive stars.

D) The rotation rate increases and results in a disk of material around a protostar.

When does a protostar become a true star?

A) when the star is 1 million years old

B) when the central temperature reaches 1 million Kelvin

C) when nuclear fusion begins in the core

D) when the thermal energy becomes trapped in the center

E) when the stellar winds and jets blow away the surrounding material

C) when nuclear fusion begins in the core

When does a star become a main-sequence star?

A) when the protostar assembles from a molecular cloud

B) the instant when hydrogen fusion first begins in the star's core

C) when the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium

D) when a star becomes luminous enough to emit thermal radiation

E) when hydrogen fusion is occurring throughout a star's interior

C) when the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium

What prevents a brown dwarf from undergoing nuclear fusion?

A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.

B) There is not enough mass to maintain nuclear reactions in a self-sustaining way.

C) The surface temperature never rises high enough for the radiation to be trapped and heat their interior to the temperatures required for nuclear fusion.

D) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.

E) There are too many heavy elements and not enough hydrogen for fusion to occur in a self-sustaining way.

A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.

What is the eventual fate of a brown dwarf?

A) It remains the same forever.

B) It gradually cools down and becomes ever dimmer.

C) It gradually contracts and heats up until nuclear fusion ignites in its interior and it

becomes a faint star.

D) It becomes ever denser and hotter until it becomes a white dwarf.

E) Gravity ultimately "wins" and it becomes a small black hole.

B) It gradually cools down and becomes ever dimmer.

what is the greatest mass a newborn star can have

a. 20 solar masses

b. 50 solar masses

c. 10 solar masses

d. 200 solar masses

e. 100 solar masses

d 200 solar masses

No stars have been found with masses greater than 100 times our Sun because

A) molecular clouds do not have enough material to form such massive stars.

B) they would fragment into binary stars because of their rapid rotation.

C) they would generate so much power that they would blow themselves apart.

D) they shine exclusively at X-ray wavelengths and become difficult to detect. E) they are not bright enough to be seen nearby

C) they would generate so much power that they would blow themselves apart

what do astronomers mean when they say we are all "star stuff"?

a. that the sun formed from the interstellar medium: the "stuff between the stars

b. that life would be impossible without energy from the sun

c. that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cones

d. that earth formed at the same time as the sun

e. that the universe contains billions of stars

c. that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cones

What prevents a brown dwarf from undergoing nuclear fusion?

A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.

B) There is not enough mass to maintain nuclear reactions in a self-sustaining way.

C) The surface temperature never rises high enough for the radiation to be trapped and heat their interior to the temperatures required for nuclear fusion.

D) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.

E) There are too many heavy elements and not enough hydrogen for fusion to occur in a self-sustaining way.

A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.