Lecture_13

Lecture_13 - 1 Star Birth Star Birth Our Goals for Learning...

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Unformatted text preview: 1 Star Birth Star Birth Our Goals for Learning How do stars form? How massive are newborn stars? REVIEW: We can measure apparent brightness and distance for thousands of stars and therefore calculate their LUMINOSITY (energy output in watts). We can use the spectrum of the star to derive its TEMPERATURE. Binary star systems reveal the MASS and RADII of many types of stars. Put all this information in a single plot of Luminosity vs Temperature and we get the H-R diagram. Most stars lie along a Main Sequence (MS) determined by mass . Stars not on the MS are either Giants or Dwarfs, a result of stellar evolution. How do stars form? How do stars form? Stars are born in molecular clouds consisting mostly of hydrogen molecules. Stars form in places where gravity can overcome thermal pressure in a cloud Cloud heats up as gravity causes it to contract Conservation of energy Contraction can continue if thermal energy is radiated away Spitzer Infrared Space Telescope image of a star-forming hydrogen cloud Star-forming clouds emit infrared light because of the heat generated as stars form in the collapsing cloud VISIBLE LIGHT VIEW INFRARED Another infrared view obtained by the Spitzer Infrared Space Telescope Infrared light from the warm Orion cloud Orion Nebula is one of the closest star- forming clouds Visible light view of Orion 2 As gravity forces a cloud to become smaller, it begins to spin faster and faster Solar Solar-system formation is a system formation is a good example of star birth good example of star birth Conservation of angular momentum The gas always settles into a spinning disk because collisions between particles destroy the inward radial motion, but all particles partake in the rotation. Angular momentum leads to: Rotation of the protostar Disk formation and sometimes Jets from protostar or Fragmentation into binary or multiple stars How do we know? THE REAL THING Hubble Space Telescope pictures DISK JET Protostar Protostar to Main Sequence to Main Sequence The large protostar contracts and heats until its core temperature is sufficient for hydrogen fusion Contraction ends when energy released by hydrogen fusion balances energy radiated away from the surface (photosphere) For a star like the Sun, this process takes about 50 million years (less time for more massive stars) 3 Summary of Star Birth 1. Gravity causes gas cloud to 1....
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This note was uploaded on 02/20/2012 for the course ASTRO 3 taught by Professor Mclean during the Spring '11 term at UCLA.

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Lecture_13 - 1 Star Birth Star Birth Our Goals for Learning...

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