SITES of STAR FORMATION |
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In 1 million years, a spiral arm moves around 65 light years with respect to the disk material. This is small compared to the size of our Galaxy; the stellar disk of our Galaxy is around 100,000 light years across.
We know that massive stars have short lifetimes--for example, a 20 Solar mass star lives for only a few million years. Massive stars indicate recent star formation and thus mark star formation regions. If we saw O and B stars distributed uniformly in the disk of our Galaxy we would infer that star formation took place everywhere in the Galaxy.
Star Formation Takes Places in large Interstellar Medium Clouds Known as Giant Molecular Clouds
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Trifid Nebula in Sagittarius, HII region |
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Why is dust such an efficient blocker of starlight (compared to the vastly more abundant gas-- recall)?
Giant Molecular Clouds (GMC) -- It is well-established that GMCs are the clouds in which star formation occurs. Orion, Orion nebula, You tube Flythrough. |
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One sees the reflection of blue light by the dust particles in the cloud. |
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