Abstract
USING the Nagoya telescope1, Uchida et al.2 found an unusual helical filamentary structure, spinning about its long axis, in the L1641 cloud in the Orion cloud complex. Noting that this structure is consistent with a helically twisted magnetic field inferred from optical polarization observations3,4, they argued that the helical filament is a manifestation of torsional magnetohydrodynamic (Alfvén) waves draining angular momentum from a nearby massive cloud, thus promoting collapse and star formation. Here we present an alternative interpretation. We suggest that the Orion molecular cloud complex formed through the Parker instability5 (the buoyancy of a magnetic field entrained in matter), and that the helical filament is the result of spinning gas falling along the magnetic field and twisting it. The twisted magnetic field, unlike a purely planar field, suppresses the Parker instability on small scales, allowing the generation of finite clouds rather than general turbulence.
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Shibata, K., Matsumoto, R. Formation of giant molecular clouds and helical magnetic fields by the Parker instability. Nature 353, 633–635 (1991). https://doi.org/10.1038/353633a0
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DOI: https://doi.org/10.1038/353633a0
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