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What do we mean by the interstellar medium? |
the gas and dust that lies in between the stars in the Milky Way galaxy |
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The interstellar clouds called molecular clouds are _______. |
the cool clouds in which stars form |
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Which of the following types of molecule is the most abundant in an interstellar molecular cloud? |
H2 |
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Interstellar dust consists mostly of _____ |
microscopic particles of carbon and silicon |
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Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds? |
infrared |
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Suppose you look at a star that can be seen through the edge of a dusty interstellar cloud. The star will look _______ than it would if it were outside the cloud. |
dimmer and redder |
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Most interstellar clouds remain stable in size because the force of gravity is opposed by _______ within the cloud. |
thermal pressure |
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What kind of gas cloud is most likely to give birth to stars? |
a cold, dense gas cloud |
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How are magnetic fields thought to affect star formation in molecular clouds? |
They can help resist gravity, so that more total mass is needed before the cloud can collapse to form stars. |
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Which of the following statements is probably true about the very first stars in the universe? |
They were made only from hydrogen and helium. |
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What is a protostar? |
a star that is still in the process of forming |
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Which of the following phenomena is not commonly associated with the star formation process? |
intense ultraviolet radiation coming from a protostar |
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What law explains why a collapsing cloud usually forms a protostellar disk around a protostar? |
conservation of angular momentum |
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What can we learn about a star from a life track on an H-R diagram? |
the surface temperature and luminosity the star will have at each stage of its life |
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When does a protostar become a main-sequence star? |
when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space |
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Approximately what core temperature is required before hydrogen fusion can begin in a star? |
10 Million K |
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Which star spends the longest time in the protostellar phase of life? |
a 1 solar mass star |
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What is the approximate range of masses that newborn main sequence stars can have? |
0.1 to 150 solar masses |
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The vast majority of stars in a newly formed star cluster are ______. |
less massive than the Sun |
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Which of the following statements about brown dwarfs is not true? |
Brown dwarfs eventually collapse to become white dwarfs. |
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