Recently obtained Hubble Space Telescope WFPC2 images of the Crab Nebula show that the emission-line filaments are dominated by structures that morphologically appear to be the result of magnetic Rayleigh-Taylor (R-T) instabilities at the interface between the pulsar-driven synchrotron nebula and a shell of sweptup ejecta. We replace this morphological argument with a quantitative treatment of the growth rate and characteristic wavelength of such instabilities. Using published data on the rate of expansion of the synchrotron nebula and the density of the ejecta, together with a wavelength for the instability measured from the WFPC2 images, we calculate a magnetic field strength of -540 J1.G. This is within a factor of 2 of the canonical minimum energy equipartition field of 300 J1.G, and probably closer than that to a more realistic estimate of the field at the edge of the Crab.
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Hester et al. (1996) studied this question.