Lecture 20…The Formation of Stars: where and how Nature provides a hint: young star clusters The...
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![Page 1: Lecture 20…The Formation of Stars: where and how Nature provides a hint: young star clusters The proto- typical object.](https://reader036.fdocuments.in/reader036/viewer/2022062409/5697bfde1a28abf838cb23f3/html5/thumbnails/1.jpg)
Lecture 20…The Formation of Stars: where and how
Nature provides a hint: young star clusters
The proto-typical object
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A star cluster with O Main Sequence stars cannot be more than a few million years old. It
may still retain information about the processes of formation
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The prime example: M42, the Orion Nebula
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Another characteristic of star formation regions, Dark Clouds
Prior to late 1960’s the nature of the connection between these and star formation was not clear
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What causes the red glow near young star clusters?
Answer: photo- ionization and recombination of Hydrogen by ultraviolet starlight
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Some physics of the hydrogen atom: “quantized” energy levels
Electrons can only be in certain states, with certain energies
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“Transitions” between states
via absorption or emission of light
Ionization by ultraviolet light with 91.2 nm
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Now talk about molecules (explanation later). They have quantized energy levels, too
Wavelengths of molecular transitions typically from 0.1 millimeter to several millimeters
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Examples of simple, astrophysically-relevant molecules
• Water
• Carbon Monoxide
• Molecular hydrogen
• ammonia
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Technology for radiotelescopes operating at millimeter
wavelengths came of age in late 1960’s
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Observations showed huge clouds of molecular gas at dark clouds
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Orion to the eye and in molecules
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The Milky Way is filled with these molecular clouds
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Summary of Molecular Clouds
• They are to be found wherever stars are forming• The molecular gas is the “raw material” from
which stars are formed• Roughly 2500 “giant molecular clouds/star
formation regions” in the Milky Way• Temperatures in these clouds as cold as 10K• Remaining questions: (a) How do stars form from
this gas? (b) What is the chemistry of these clouds?