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Star Formation

0. Star Formation. 0. Giant Molecular Clouds. Barnard 68. Infrared. Visible. Star formation ← collapse of the cores of giant molecular clouds : Dark, cold, dense clouds obscuring the light of stars behind them. 0. Parameters of Giant Molecular Clouds. Size: r ~ 50 pc.

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Star Formation

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  1. 0 Star Formation

  2. 0 Giant Molecular Clouds Barnard 68 Infrared Visible Star formation← collapse of the cores ofgiant molecular clouds:Dark, cold, dense cloudsobscuring the light of stars behind them.

  3. 0 Parameters of Giant Molecular Clouds Size: r ~ 50 pc Mass: ~ 106 Msun Temp.: ~ 20 K Density: ~ 100 – 300 cm-3 Hot, dense cores: r ~ 0.05 - 1 pc M ~ 10 - 100 Msun T ~ 100 - 200 K n ~ 107 – 109 cm-3 Bok globules: r ~ 1 pc M ~ 1 - 1000 Msun T ~ 10 K n ≥ 104 cm-3

  4. 0 Trifid Nebula Bok Globules

  5. 0 Globules Bok Globules: ~ 10 – 1000 solar masses; Contracting to form protostars

  6. 0 Globules Evaporating Gaseous Globules (“EGGs”): Newly forming stars exposed by the ionizing radiation from nearby massive stars

  7. 0 Free Fall of a GMC Core

  8. 0 Fragmentation • MJ ~ T3/2r-1/2 • ~ r-1/2 • during isothermal collapse • Fragmentation => Stars do not form isolated, but in large groups, calledOpen Clusters of Stars. Open Cluster M7

  9. 0 Pre-Main-Sequence Evolution Hydrostatic equilibrium reached → Adiabatic collapse → Heating Isothermal collapse of the protostar: Gravitational energy release in equilibrium with radiative cooling: Hayashi Track Isothermal collapse → Formation of a protostellar core

  10. 0 Protostars Protostars = pre-birth state of stars: Hydrogen to Helium fusion not yet ignited Still enshrouded in opaque “cocoons” of dust => barely visible in the optical, but bright in the infrared.

  11. 0 Pre-Main-Sequence Evolution Star emerges from the enshrouding dust cocoon Hayashi Track First thermonuclear reactions: p + 21H → 32He + g Radiative core develops p + p → 21H + e+ + ne and 126C-burning steps of CNO cycle set in Core expands; T drops 126C supply exhausted; final adjustment to ZAMS

  12. 0 → O/B associations Young Star Clusters Stars fully evolved towards ZAMS 8 million years Containing very young, hot O/B stars Luminosity Stars still contracting and evolving towards ZAMS ZAMS 30 million years Temperature

  13. 0 HII Regions The Strömgren Sphere rs ~ 0.3 pc for a typical O6 star H ionization rate = recombination rate N>13.6 eV = (4/3) p rs3 nH2a a ≈ 3.1x10-13 (T/8000 K)-1/2 cm3 s-1 rs = [(3 N>13.6 eV) / (4 p nH2a)]1/3

  14. T Tauri Stars • Intermediate stage between dust-enshrouded (IR sources) and ZAMS • Large-amplitude variability on time scales of days • 0.5 – 3 M0 • Strong emission lines (Balmer, Ca II, Fe) • Forbidden lines [O], [SII] • Often associated with protostellar/protoplanetary disks

  15. 0 Protostellar Disks and Jets – Herbig Haro Objects Disks of matter accreted onto the protostar (“accretion disks”) often lead to the formation of jets (directed outflows; bipolar outflows): Herbig Haro Objects

  16. 0 Protostellar Disks and Jets – Herbig Haro Objects (II) Herbig Haro Object HH34

  17. 0 Protostellar Disks and Jets – Herbig Haro Objects (III) Herbig Haro Object HH30

  18. 0 The Orion Nebula: An Active Star-Forming Region

  19. 0 The Trapezium The 4 trapezium stars: Brightest, very young (less than 2 million years old) stars in the central region of the Orion nebula Only one of the trapezium stars is hot enough to ionize hydrogen in the Orion nebula Infrared image: ~ 50 very young, cool, low-mass stars X-ray image: ~ 1000 very young, hot stars The Orion Nebula

  20. 0 Kleinmann-Low nebula (KL): Cluster of cool, young protostars detectable only in the infrared The Becklin-Neugebauer Object (BN): Hot star, just reaching the main sequence Spectral types of the trapezium stars B3 B1 B1 O6 Visual image of the Orion Nebula Protostars with protoplanetary disks

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