Term
| What is the range of timescales for a star to reach the main sequence? |
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Definition
| From 10,000 years for the most massive stars (100 solar masses) up to 100 million years for the least massive stars (0.1 solar masses) |
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Term
| CNO chain of thermonuclear reactions is efficient if |
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Definition
| a star's core temperature is greater than 15,000,000K |
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Term
| When does a star arrive at the main sequence? |
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Definition
| The instant when hydrogen fusion gest ignited in the star's core |
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Term
| The interstellar medium contains |
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Definition
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Term
| When starlight passes through interstellar dust |
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Definition
| It gets fainter and The blue light tends to be scattered more efficiently than red light |
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Term
| What process stops the contraction of a protostar? |
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Definition
| Initiation of thermonuclear reactions in its core |
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Term
| If a protostar's mass is less than 0.08 Msun, it becomes a: |
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Definition
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Term
| Why can’t a cloud with less than 0.08 solar masses become a star? |
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Definition
| Its temperature will never rise to 10 million K required for initiation of thermonuclear fusion |
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Term
| Structures that are usually associated with formation of a young star include |
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Definition
| bipolar outflows, collimated jets, stellar winds, and circumstellar disks |
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Term
| A molecular cloud is unstable to gravitational collapse if its |
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Definition
| Mass is greater than about a few hundred solar masses and gravitational force is greater than the thermal pressure force |
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Term
| Why do protostars are surrounded by rotating disks of gas and dust? |
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Definition
| If an initial cloud spins at a slow rate, its spin increases as the clouds contracts and Conservation of angular momentum |
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Term
| What is the energy source that heats a contracting protostar? |
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Definition
| Gravitational potential energy released as the matter is pulled inward |
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Term
| Why do astronomers think that stars are formed from clouds of gas and dust? |
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Definition
| Astronomers observe young star clusters with gas and dust around them, Observations in the infrared and microwave bands reveal protostars shrouded by gas and dust clouds, and Computer models predict that if a cloud has enough mass it will gravitationally contract, break up into fragments, heat up each of it, and form a star |
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Term
| The initial process in the formation of a protostar is represented by |
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Definition
| gravitational collapse of gas and dust |
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Term
| Coronal gas in the interstellar medium is mostly formed due to |
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Definition
| shock waves produced by stellar winds and supernova explosions |
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Term
| Regions of ionized hydrogen heated to 10,000K are visible in the optical bands due to |
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Definition
| photoexcitation, photoionization and recombination processes |
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Term
| Cold and warm neutral atomic hydrogen is observed via |
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Definition
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Term
| Dust grains heated by stellar radiation are good emitters in |
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Definition
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Term
| Molecular clouds represent |
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Definition
| cold and dense complexes of molecular hydrogen |
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Term
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Definition
| 99% of the total mass of the interstellar medium |
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