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Chapter 6: Planetological foundations for origins of life

Chapter 6: Planetological foundations for origins of life. A. Major questions in star formation:. 1. What determines the stellar mass spectrum (the “initial mass spectrum” IMF)? 2. How do individual stars/disks/jets form?

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Chapter 6: Planetological foundations for origins of life

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  1. Chapter 6: Planetological foundations for origins of life

  2. A. Major questions in star formation: 1. What determines the stellar mass spectrum (the “initial mass spectrum” IMF)? 2. How do individual stars/disks/jets form? 3. Do all stars form in the same way? (both low and high mass stars)? 4. How does star formation affect planet formation? [what accounts for weird extrasolar planetary systems?]

  3. Star formation in the Milky Way: Stars form in massive clouds of dusty, cold, molecular gas - To detect gas - map millimetre wave emission from carbon monoxide molecule. - To detect dust - map sub-millimetre emission from dust grains (eg. Use James Clerk Maxwell Telescope – on top of Mauna Kea volcano - Hawaii)

  4. The Galactic Center in visible Light Star formation in the Galaxy

  5. Optical images and infrared images of the Orion Nebula IRAS satellite: sensitive at wavelengths 10 – 100 microns

  6. Orion GMC - and the Orion Nebula Cluster Most stars form as members of star clusters and not in isolation: Major clue to origin of IMF….. Johnstone et al (2000)

  7. Super-massive star clusters Star cluster in the Large Magellanic Cloud, (HST image)

  8. The Origin of Stellar Masses: Formation of Molecular Cloud Cores? • Numerous small dense gas “cores” within a clump. Individual stars form in cores – typically 0.04 pc in size (Motte et al 2001)

  9. Origin of stellar masses – have same distribution in mass as small gas cores

  10. How do nearby stars form in molecular clouds? • Clouds are turbulent • Turbulence produces density fluctuations that resemble rotating cores. • Simulations and theory show that “turbulent fragmentation” can produce core mass spectrum. • Turbulence is universal – may imply universality of the IMF

  11. Largest star formation simulation ever done: 100,000 cpu hours! - Begin with: cloud is 1.2 light-years across, contains 50 solar masses of gas. - Initial turbulence in the cloud fragments it – then gravity pulls regions together to form “cores”

  12. Turbulence and star cluster simulation • shows highly filamented structure • shows many small overdense regions which can be identified with “cores”. • cores formed through turbulent fragmentation Tilley & Pudritz (2004)

  13. Massive star formation – filamentary accretionFLASH – Adaptive Mesh Refinement (AMR) simulation: (Banerjee, Pudritz, & Anderson 2006: start with TP04 ) • Collapse along filament into a forming disk...

  14. Tilley & Pudritz ‘04 – hydro simulations of turbulent fragmentation

  15. Simulating star formation in magnetized clouds (Tilley & Pudritz 2005) Turbulence breaks up clouds into dense cores in which stars form

  16. Gravitational collapse of core: formation of a star/disk/jet Infrared image Barnard 68 (Alves et al 2001): excellent fit with Bonner-Ebert model (pressure truncated isothermal sphere)

  17. Disks around young – and old stars Orion Proplyd – star in formation Submm image of Epsilon Eridanni Greaves et al (1998)

  18. Disks in the Orion nebula…

  19. Disk structure: reprocessing stellar radiation Submm Infrared Optical Radiative resprocessing: hydrostatic equilibrium disk models 1: Disk Surface Tds 2: Disk Interior Ti Chiang and Goldreich (1997)

  20. Chemisty in protoplanetary disks: mm wavelengths (Aikawa et al 2002): distribution of T (top row) and n (bottom row), in D’Allessio et al model. Columns correspond to 3 different accretion rates. Top: dark is low CO/H2, grey is higher:

  21. H2 UV, NIR, MIR H2O ro-vib OH v=1 CO v=1 CO v=2 1 AU ~200 K 10 AU ~50 K 0.1 AU ~1000 K Molecular Probes of Inner Disks

  22. Hydrocarbons in massive protostar NGC 7538 Are the organic precursor molecules for life common in planet-forming disks? • The MIR is rich in transitions of organic molecules

  23. Collapse & disk formation: Density(Banerjee & Pudritz, 2004)

  24. Jets are strongly correlated with disk properties… what produces jets? Magnetic fields are crucial…

  25. Collapse of a magnetized core: produce outflows by “magnetic centrifuge”. (Banerjee & Pudritz 2006)

  26. Jets as disk winds: (Banerjee & Pudritz 2006) - launch inside 0.07 AU (separated by 5 month interval) - jets rotate and carry off angular momentum of disk - spin of protostellar core at this early time?

  27. Universality – do all stars form in the same way? Brown dwarfs: observed to have disks and jets! (eg. Whelan et al 2006 for 60 MJupiter BD). Massive YSO jets: massive accretion > 0.001 solar masses/yr prevent radiation pressure from blowing away the infall: -> massive star formation by accretion picture too? (McKee & Tan 2003) - some massive stars observed to have both disks and jets.

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