Summary Chapter 11 Star form

Summary Chapter 11 Star form - a) supernova explosion b)...

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Chapter Summaries Chapter 11: The Formation of Stars Short review of Ch 10 ( ISM) Molecular Clouds consist of gas and dust (note: molecules form in molecular clouds) ISM in the Milky Way: 70% H, 28% He, 2% heavy elements Temperature in molecular clouds: 10 – 30 K Molecular clouds are observed in the radio part of the electromagnetic spectrum CO (carbon monoxide) is the main molecule observed Interstellar dust (made of Carbon, Oxygen, Silicon, and Iron) Dust is observed in the Infrared part of the electromagnetic spectrum Interstellar Reddening dust grains block out shorter wavelengths (bluer photons) dust grains emit longer wavelengths (redder photons) -------- Stars form in molecular clouds in the Interstellar Medium (ISM) (Molecular cloud must be very dense to create a single star) 1) dark cloud cores 2) gravitational collapse 3) protostar stage (planet formation, too) 4) main sequence star Star formation is triggered by shocks:
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Unformatted text preview: a) supernova explosion b) ionization fronts of hot, massive O & B star radiation c) collisions of giant molecular clouds d) spiral arms of galaxies Gravity starts contraction Gravity and thermal pressure (tug of war) Mass of molecular clouds are about 100 solar masses to be able to form stars Magnetic Fields, rotation, and turbulence can prevent or slow a stars contraction Molecular clouds are a place where stars form in multiples Bok Globules Herbig-Haro Objects T Tauri Stars Protostar Main Sequence Stars (fusion at core balances gravitational force) First Stars: contained only H and He no CO (that would cool collapsing molecular cloud) warmer environment that present epoch of clouds huge stars formed (greater than 30 solar masses) Gravitational Equilibrium (gravity inwards = pressure outwards) Stellar Mass: low limit: 0.08 M Sun upper limit: about 100 M Sun...
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