1 / 20

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.

aysha
Download Presentation

Star Formation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related