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| Star Birth and the Main Sequence |
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1. | The Jeans critical density formula for the gravitational collapse of a molecular cloud depends both on the total mass of the cloud and the average mass of the particles in the gas. Why do you think it depends on the second quantity? Does the form of the Jeans critical mass formula support your interpretation? |
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2. | In the discussion of brown dwarfs, it was argued that the presence of the element lithium is a strong indicator that the object has never undergone core hydrogen fusion because lithium is quickly destroyed in fusion reactions. How would you counter the argument that this is not a good test because fusion takes place in the core but we observe the surface of a brown dwarf? |
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3. | Why can I make the following statement with confidence: "Virtually all O and B main sequence stars that have ever lived are now dead, but no M main sequence star has yet left the main sequence"? |
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4. | Why can't we use the 21 cm spin flip transition in the radio spectrum to map dark molecular clouds? |