Exam 16: Star Birth

A) a hot,dense gas cloud
B) a cold,dense gas cloud
C) a cold,low-density gas cloud
D) a hot,low-density gas cloud

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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.

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A) A main-sequence star is hotter and brighter than it was as a protostar.
B) A main-sequence star is cooler and dimmer than it was as a protostar.
C) A main-sequence star is cooler and brighter than it was as a protostar.
D) A main-sequence star is hotter and dimmer than it was as a protostar.

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A) All rotating objects slow down over time.
B) Magnetic fields can transfer angular momentum to the protostellar disk and protostellar winds can carry angular momentum away.
C) The onset of fusion causes the rotation rate to slow dramatically.
D) Magnetic fields of other stars interact with the magnetic fields of the protostars,slowing its rotation.

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A) It is blocked by dust and its energy is thereby lost.
B) It is absorbed by dust,which heats the dust grains so that they emit the absorbed energy as infrared light.
C) It is reflected by dust back to the star from whence it came.
D) It passes through the cloud unaffected.

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A) to the right of the main sequence,and lower down than the Sun
B) to the right of the main sequence,and higher up than the Sun
C) to the left of the main sequence,and higher up than the Sun
D) Nowhere-only stars that have fusion in their cores can be shown on H-R diagrams.

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A) two interstellar gas clouds happen to contract so close together that there's no room for a disk or planets.
B) the protostellar disk around a protostar has enough material to form a second star.
C) gravity pulls two neighboring protostars quite close together,but angular momentum causes them to orbit each other rather than colliding.
D) a protostar emits two jets,each of which turns into a star.

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A) 1%
B) 10%
C) 50%
D) 98%

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A) 1
B) 3
C) 10
D) 30
E) 200

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A) They can help resist gravity,so that more total mass is needed before the cloud can collapse to form stars.
B) They accelerate the star formation process.
C) They allow small stars to form in isolation within gas clouds.
D) None-there are no magnetic fields in interstellar space.

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A) when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space
B) when a piece of a molecular cloud first begins to contract into a star
C) when it becomes luminous enough to emit thermal radiation
D) at the instant that the first hydrogen fusion reactions occur in the protostar's core

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A) from 1 million years for the most massive stars up to 10 million years for the least massive stars
B) from 1 million years for the most massive stars up to 100 million years for the least massive stars
C) from 1 million years for the least massive stars up to 10 million years for the most massive stars
D) from 1 million years for the least massive stars up to 100 million years for the most massive stars
E) about 30 million years for all stars,whatever mass

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A) the clouds in which elements such as carbon,nitrogen,and oxygen are made.
B) clouds that are made mostly of complex molecules such as carbon dioxide and sulfur dioxide.
C) the hot clouds of gas expelled by dying stars.
D) the cool clouds in which stars form.

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The low end is set by the resistance to ...

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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 flattened disk of material around a protostar.
E) The rotation increases the speed of collapse and produces more massive stars.

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A) shrinks and cools.
B) shrinks and maintains a constant temperature.
C) shrinks and heats.
D) expands and cools.

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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.

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