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Ch 11: Star Formation

Ch 11: Star Formation. Star formation/birth is ongoing in our galaxy: e.g. sun is younger than oldest stars; short lived stars exist. How does it occur ? youngest stars found near gas clouds  somehow: gas clouds make stars. Giant Molecular Cloud :

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Ch 11: Star Formation

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  1. Ch 11: Star Formation • Star formation/birth is ongoing in our galaxy: • e.g. sun is younger than oldest stars; short lived stars exist • How does it occur ? • youngest stars found near gas clouds •  somehow: gas clouds make stars • Giant Molecular Cloud : • overall: ~105 Msun ; ~50pc ; few K • with dense cores : ~1pc ; ~1 Msun • this is where new stars are born • they will also be born in groups

  2. (1b) Example : M16

  3. (2) Support vs collapse • Usually, dense cores are supported by: • Gas pressure • Turbulence • Magnetic fields (magnetic pressure) • Rotation (centrifugal support) • Collapse triggered by shock waves from: • Supernova explosions • Strong star winds • Cloud collisions • Spiral arm passage

  4. (3) Collapse Gravitational contraction :  cloud fragments  spins up & flattens & heats  protostar & protostellar disk  planets form in disk  jets & winds common

  5. (3b) Examplesdisks Sketch  disk formation Disks with proto-stars & winds Sketch: Planets form in disk

  6. (3c) Examples : Jets Jets

  7. (4) Trajectory on H-R diagram • contraction releases gravitational energy = proto-star • enters far right & low (cool & dim) • moves left & up (hotter & brighter) • H fusion in core starts = real star • arrives on main sequence (ZAMS) • mass important: • High M : fast & top-left • Low M : slow & low-right Often hidden

  8. (4b) Examples • Stars form in clusters – many together • range of mass ( 0.08 – 50 Msun ) • Many more low mass than high mass • HR diagram shows all these : Pleiades: older cluster Very young cluster

  9. (5) Star Formation Regions • Complex : global evolution • O stars ionize surrounding gas •  Pink HII regions • Winds blow cavity; disperse gas

  10. (5b) Example: Orion Optical Infrared Optical Infrared

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