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WHERE STARS ARE BORN

WHERE STARS ARE BORN. The Interstellar Medium (ISM). The space between the stars looks empty . . . But it’s not!. Gas. Dust. ~ 0.0001 cm. * Mainly hydrogen + helium * Avg density  1 – 10 atoms/cm 3 * 99% of ISM. * Tiny grains (‘smoke’). * Silicates, carbon, ice (?)

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WHERE STARS ARE BORN

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  1. WHERE STARS ARE BORN

  2. The Interstellar Medium (ISM) The space between the stars looks empty . . . But it’s not!

  3. Gas Dust ~ 0.0001 cm * Mainly hydrogen + helium * Avg density  1 – 10 atoms/cm3 * 99% of ISM * Tiny grains (‘smoke’) * Silicates, carbon, ice (?) * Avg density  1 grain/million m3

  4. ‘Whirlpool’ Galaxy

  5. Looking at a galaxy from the inside.

  6. Looking for Gas

  7. Rosette Nebula Emission Nebulae * Ultraviolet photons from hot stars are absorbed by gas atoms – cause gas to glow.

  8. Great Orion Nebula

  9. Trifid Nebula North America Nebula

  10. Hot Stars H atoms UV Earth

  11. UV Hydrogen atom Electron ejected Electron recaptured Photon emitted

  12. Red Balmer emission Line

  13. Molecules – mainly hydrogen (H2). Carbon monoxide (CO) in Orion

  14. Looking for Dust

  15. Reflection Nebulae Pleiades Star Cluster * Glows due to scattered (reflected) starlight. * Dust scatters blue light more efficiently than red light.

  16. Molecules abundant here Dark Nebulae

  17. Emission nebula ‘Horsehead’ Nebula Reflection nebula

  18. Star Formation

  19. * Results from collapse of a molecular cloud. • Cloud collisions • Supernova blast wave • Expanding emission nebula • Galactic density wave

  20. p. 271

  21. Molecular Cloud Shrink & heat Central temp  10 million K: Hydrogen fusion ignites ‘protostars’ (on main sequence)

  22. Star birth in the Eagle Nebula

  23. Forming star? Star birth in the Trifid Nebula

  24. * Accretion disk may form around young stars . . . Bipolar Flow

  25. Bipolar Flow Disk p. 273

  26. Protostellar Disks

  27. ‘Evolutionary tracks’ on the HR diagram: Time required for contraction to main sequence depends on mass. pgs. 274-5

  28. Limits to Star Formation

  29. Protostar mass < 0.08 M: No hydrogen ignition: ‘Brown Dwarf’

  30. The ‘Pistol’ Star M > 100 M Star disrupted by the pressure of photons.

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