18_-_ISM - 18 - The interstellar medium: a mix of dust,...

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18 - The interstellar medium: a mix of dust, gas, photons, cosmic rays and a few stars Lyman Spitzer 2 Prospectus •Space is filled with gas, dust, stars, cosmic rays, and light. •How do dust and gas influence the formation of stars. •How are dust and molecules formed and destroyed? 3 Interstellar dust and gas •Dust and gas are mostly found in spiral galaxies. •HI gas in the Milky Way M87 “no” ISM Dust Lane 4 The Interstellar Medium •Stars are born from the gas and dust, collectively known as the interstellar medium, ISM. •During their lifetime, stars may return some material to the ISM through surface winds or explosive events. •In supernova explosions, most of the star is dispersed throughout the ISM.
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5 Composition of the ISM • Hydrogen is by far the most common element in the ISM Molecular (H 2 ) Neutral (HI) Ionized (HII) • Also contains helium and other elements. The solid component is in the form of dust . 6 All the Players PDR HII Regions (hot young stars, H + Molecular Gas and Dust Diffuse HI in the ISM Photo Dissociation Regions 7 Photodissociation Regions: the no-man’s land between HII and HI regions • Shielded from H ionizing radiation, but is exposed to lower energy UV and X-rays • Dust is the dominant UV absorber • Contains nearly all atomic and molecular gas • Origin of much of IR radiation from ISM dust continuum PAH features fine structure lines 8 Photodissociation Regions
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9 HII Regions in our Galaxy: Location, Location , Location Orion Nebula M42 (Near) W3 (Far) Optical Infrared OSU Image Gallery and DSS PDR 10 Hidden Star Formation 11 The Antennae, galaxies in collision! Infrared Image
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This note was uploaded on 04/05/2009 for the course ASTRO 3332 taught by Professor Houck,j during the Spring '09 term at Cornell.

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18_-_ISM - 18 - The interstellar medium: a mix of dust,...

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