Magnetic fields and star formation
While the Standard Model is not well supported by current observations (Mac Low & Klessen 2004), there is no conclusive evidence in favour of either model. Crutcher (2004) concluded that: ‘ there does not seem to be a single driver of star formation ’ , in so far as star formation appears to be a driven by both supersonic turbulent activity and ambipolar diffusion within molecular clouds. Studies of molecular cloud core morphologies encode important information about the processes of cloud fragmentation and core formation. Their intrinsic shapes may reveal whether they have formed as a result of turbulent flows, in which case they are predicted to have slightly prolate, random and triaxial cores (Gammie et al. 2003). Whereas those that have formed as a result of magnetically regulated processes, such as ambipolar diffusion, are predicted to be oblate, flattened along the field lines, with core’s minor axis parallel to the large -scale cloud field (Ciolek & Basu 2006). Jones & Basu (2002) claim that observations support these magnetically regulated models, since observations reveal that molecular clouds tend to be oblate. This claim is strongly contested by Ward- Thompson et al. (2000), who, through the sub-millimetre polarimetry observations on four quiescent cores, revealedthat the field was misaligned. At the same time. Tassis et al. (2009) discovered, in their statistical analysis of observations of twenty-four clouds, a preference for models with oblate cores and minor deviations from the core minor axis.
Conclusions
This is no conclusive evidence at present in favour of either of the two extreme paradigms of star formation. Though opinion may be divided, and strongly so, on the role that magnetic fields plays in star formation. The relative successes of all the various theories and models of star formation and the processes that drive them are measured by observation. What is apparent from this debate is the paucity of observations of giant molecular clouds and their associated sub-structures. Observations to date are relatively limited in terms providing a complete understanding of magnetic field evolution. However, advances in sub-millimetre polarimetry will trace the magnetic field across whole molecular clouds and their associated sub-structures within to provide an unprecedented view of our Galaxy. These polarization maps will not only trace the magnetic field lines but will also provide a means to estimate its strength as it courses across giant molecular clouds. These maps may provide the key to unlock the mysteries that surround the process that drive star formation. And in any eventually, they will make an enormous contribution to our understanding of the pervasive magnetic fields, the dusty molecular clouds and grains that they contain.
Bibliography
Allen, A. et al. (2003) ‘ Collapse of magnetized singular isothermal toroids. ii. rotation and magnetic braking’, The Astrophysical Journal 599: 363-79 Beichman, C. et al. (1986) ’Candidate solar -type protostars in nearby m olecular cloud cores’, The Astrophysical Journal 307: 337-49 Ciolek, G. & Basu, s. (2006) ‘ Formation and collapse of nonaxisymmetric protostellar cores in planar magnetic interstellar clouds ’, The Astrophysical Journal 652: 442-57
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