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The Birthplace of Stars: Exploring the Interstellar Medium and Star Formation

The Interstellar Medium (ISM) may appear empty, yet it's rich with gas and dust, primarily hydrogen and helium, with an average density of 1 to 10 atoms/cm³. It plays a crucial role in star formation, where molecular clouds collapse under gravity, fueled by collisions and supernova shock waves. Within regions like the Orion Nebula and the Trifid Nebula, hot stars emit ultraviolet light, exciting surrounding gas and causing it to glow. The formation process includes protostars with accretion disks and the significant role of dust, influencing light scattering and leading to distinct reflection and emission nebulae.

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The Birthplace of Stars: Exploring the Interstellar Medium and Star Formation

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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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