Provincial Star Formation

1. Provincial Star Formation Larry Morgan

2. Contents • Molecular Clouds • Protostellar Evolution (IRDCs) • Massive Star-Formation • Support Factors (Turbulence,Ambipolar diffusion, Feedback, etc.)

3. Contents • Observational Features and How to recognise them (Masers, outflows, infall) • Observational Methods • Theoretical Work • Unanswered Questions in Star Formation

4. Giant Molecular Clouds The Gould Belt spans 3000 light years and is of unknown origin. It contains many massive stars and its true composition in terms of star-formation is unknown

5. Giant Molecular Clouds Orion Molecular Cloud

6. Molecular Clouds < 100 M⊙, Typically ‘isolated’

7. IRDCs IRDCs visible by their extinction of background stars

8. IRDCs • Thought to represent earliest stages of star-formation • Dust and gas agglomerating into dense ‘clumps’

9. Class -1 YSOs In order to get from a clump to a star a lot of physics must occur

10. Star-Formation Theory

11. Class -1 YSOs • As clumps collapse the increased density results in increased temperature in the interior regions • This increased temperature means increased internal pressure • Increased density also means more efficient radiation transport!

12. Class 0 Protostars • Gravitational contraction energy goes into ionising/dissociating atoms/molecules • Protostar becomes increasingly opaque to own radiation - results in hydrostatic equilibrium

13. Angular Momentum • Major problem with mechanics of star-formation, where does the angular momentum go? • Material ejected at rotation axis in bipolar outflow, may be magnetic field role in this

14. Class 0 YSOs

15. Final Phases

16. Accretion • Mass continues to accrete onto protostar until nuclear fusion occurs. At this point stellar winds overwhelm the inward attraction and the outer layers of the protostar are thrown off • This is a big problem for massive star-formation. Theoretically, thermonuclear fusion will occur long before final mass of star is reached

17. Accretion • Theories of coalescing cores and competitive accretion in which massive YSOs are formed from smaller protostellar objects have been largely dismissed, or at least played down • New theories have postulated that accretion processes can occur post-ignition and are similar to enhanced low mass star-formation

18. Support Mechanisms • Turbulence is blamed for much that we don’t understand, both in the fragmentation of molecular clouds and in the support of clumps • In the extreme turbulence paradigm structure in the ISM is formed through turbulence, some clumps form and usually dissipate while some become dense enough to collapse under self-gravity (Compressible Turbulence)

19. Support Mechanisms • “Magnetic Fields are to astrophysicists what sex is to psychoanalysts” • -H.C.Van de Hulst

20. Support Mechanisms • In the extreme magnetic support paradigm self-gravitation is offset by ambipolar diffusion • Inherent magnetic field of molecular clouds coupled with the ions, not neutrals. Self-gravitation pulls neutrals into condensations, intensifying magnetic field. This is ambipolar diffusion. • Mass eventually overwhelms core magnetic field and causes collapse

21. Ambipolar Diffusion

22. Magnetism Vs. Turbulence, or ‘Teach the Controversy’ • Why the dispute? • Magnetic properties in molecular clouds hard to observe, or rather, inherent errors are large enough that conclusions tend to be speculative • Recent observational results claim victory for magnetic support (Crutcher, unpublished). N.B. Magnetic fields may also explain loss of angular momentum problem

23. Magnetism Vs. Turbulence, or ‘Teach the Controversy’ • Numerical Simulations incorporating compressible turbulence show IMF consistent with observations (Ballesteros-Paredes et al 2004)

24. Observational Signatures of Star-Formation Masers • Population inversion, occurs in extreme environments where collisional and radiative pumping (usually IR) can occur • Such environments are typically found in star-forming regions, e.g. the edge of an outflow or the UCHII region around a young massive star

25. Observational Signatures of Star-Formation • Masers can be specific to environment, e.g. The OH maser transitions • 1612 MHz - late-type star association • 1665 & 1667 MHz - most common maser association • 1720 MHz - trace shock fronts, associated with methanol masers Masers

26. Observational Signatures of Star-Formation • Identifying masers - transitions usually well known, OH, H2O, CH3OH, NH3 • Masing transitions much more intense than expected thermal line • Location of maser can be indicative, thermal lines should be ubiquitous, maser emission is localised Masers

27. Observational Signatures of Star-Formation Outflow

28. Observational Signatures of Star-Formation Outflow Turbulent contribution to the Gaussian thermal lines expected from a condensation of ideal gas

29. Observational Signatures of Star-Formation Infall

30. IRDCs Extinction Mapping IRDCs visible by their extinction of background stars

31. Observational Methods Extinction Mapping

32. Observational Methods Extinction Mapping

33. Observational Methods Molecular Lines

34. Observational Methods Molecular Lines

35. Observational Methods Continuum

36. Theoretical Work Simulations • Simulation follows collapse of interstellar gas cloud >1 lyr across and 50 M⊙ • Surprising results are that interactions occur early in history of cloud • Roughly 1/2 of the formed objects are ejected so quickly that they cannot accrete beyond the stage of brown dwarf

37. Theoretical Work Simulations • Results show that interactions strip available gas for accretion so that many objects are truncated in size to less than solar system size, despite large initial disk sizes • Collapse takes 266,000 yr • T - 10K -> Thermal Jeans Mass of 1M⊙ • Accretion radius set to 5 AU, resolution of disks therefore 10 AU • Binary system separation followed to 1 AU

39. Unanswered Questions in Star-Formation • What is the role of magnetic fields in the formation and evolution of massive stars? • Is there an empirically equivalent Class 0 phase for massive stars? • What determines the IMF in different environments? • What determines the mass of stars? • How is the protostellar accretion disk linked to outflows?