PCS 181 Lecture Notes - Lecture 4: Protoplanetary Disk, Milky Way, Protostar
23 Apr 2016
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This is dust and gas that occupy space between stars. 100x more gas mass than dust mass in universe. These are clouds of neutral (not ionized) hydrogen. Cold hydrogen gas is in its ground state (n=1 orbit) Hydrogen atom has 2 possible ground state configurations. Electron may undergo a spontaneous spin flip from aligned (parallel) state to opposed (anti- parallel) state. Cold neutral hydrogen clouds in space emit a wavelength: Excess energy is released as a tiny burst of radiation. =a photon of definite wavelength: =21 cm=0. 21 m. Corresponding frequency is f=1. 42x109 hz = 1. 42 ghz = 1. 42 gigahertz. This wavelength is used to map milky way galaxy, and to search for messages from extra- terrestrials. Consider a giant interstellar cold molecular h2 cloud. Random particle fluctuations in cloud act as gravitational foci to attract more material. Contracting condensates in cloud dissipate their gravitational energy as hear (infrared radiation) Core reaches 10 million k=10 x 106 k=1 x 107 k.
