Lecture 20…The Formation of Stars: where and how Nature provides a hint: young star clusters The...
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Transcript of Lecture 20…The Formation of Stars: where and how Nature provides a hint: young star clusters The...
Lecture 20…The Formation of Stars: where and how
Nature provides a hint: young star clusters
The proto-typical object
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
The prime example: M42, the Orion Nebula
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
What causes the red glow near young star clusters?
Answer: photo- ionization and recombination of Hydrogen by ultraviolet starlight
Some physics of the hydrogen atom: “quantized” energy levels
Electrons can only be in certain states, with certain energies
“Transitions” between states
via absorption or emission of light
Ionization by ultraviolet light with 91.2 nm
Now talk about molecules (explanation later). They have quantized energy levels, too
Wavelengths of molecular transitions typically from 0.1 millimeter to several millimeters
Examples of simple, astrophysically-relevant molecules
• Water
• Carbon Monoxide
• Molecular hydrogen
• ammonia
Technology for radiotelescopes operating at millimeter
wavelengths came of age in late 1960’s
Observations showed huge clouds of molecular gas at dark clouds
Orion to the eye and in molecules
The Milky Way is filled with these molecular clouds
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?