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14 Cards in this Set
- Front
- Back
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What are star forming clouds? |
dark clouds of dusty gas in interstellar space. composed of molecules (h2,CO,ect) mostly. temperature of between 10-30k and a density of about 300 molecules per cubic centimeter Gravity can create stars if it can overcum the force of thermal pressure in a cloud emission lines from molecules in a cloud can prevent a pressure buildup by converting thermal energy into infrared and radio photons (light) that esape the cloud. If this energy is escaping gravity can not pressure it into the formation of a star. star forming clouds must contain at least a few hudnred solar masses for gravity to overcome pressure typically they have a tempeture of 30k and 300 particles/cmto the power of 3. |
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Interstellar Medium |
Gas between the stars. made up of 70% hydrogen, 28%helium and 2% heavier elements in the milky way. |
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What is fragmentation of a cloud? |
gravity within a contracting gas cloud becomes stronger as the gas becomes denser and therefore overcomes pressure in smaller pieces of the cloud causing it to break apart into multiple fragments. each may go on to form a star.
large clouds can make whole clusters of stars. |
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What are properties of the first stars? |
elements like carbon and oxygen had not yet been made when stars first fomed and without co molecules to provide cooling the clouds that formed the first stars had to be considerably warmer than today's molecular clouds. they must have been more massive than most of todays stars for gravity to overcome pressure. theory suggest they never cooled below 100k which is 100msun |
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what tempeture do dusty clouds form stars? |
10-30 k |
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What is the trapping of thermal energy? |
contraction packs the molecules and dust particles of a cloud fragment close together and becomes harder for infrared and radio photons to escape thermal energy begins to build up inside increasing the internal pressure contraction slows down and the center of the cloud fragment becomes a protostar |
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What is a protostar? |
the dense centre of a cloud fragment. the stage before a main stage star. a clump of gas that will become a new star. look starlike but center is not yet hot enough for nuclear fusion. energy comes from contraction not fusion, contractoin continues until the core becomes hot enough for nulcear fusion. once contraction stops the energy released by core fusion balances energy radiated from teh surface. the star is now a main sequence star. luminosity and temperature grow as matter collects into a protostar |
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Convective conraction |
surface temp remains near 3000k while convection is the main energy transport mechanism. |
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Radiative contraction |
luminosity remains nearly constant during late stages of contraction, while radiation transports energy through star. |
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Self sustaining fusion |
core temperature continues to rise until star begins fusion and arrives on the main sequence. |
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Life tracks for different masses.... based on our sun |
our sun took 30 million years to go from protostar to main sequence but higer mass stars form faster and lower mass stars form more slowly. |
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What happens with high high and low low stars? |
stars more than 150msun blow apart and htose less than 0.08msun cannot sustain fusion and become brown dwarfs. |
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Does star formation make more low mas stars or high mass stars? |
star formation makes more, many more low mass stars. aprox 200 low mas stars to every large mass stars. |
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Degeneracy pressure |
the resistance to squeezing. |
