On the Nature of the Emission of the Crab Nebula

Extract

The emission of the Crab Nebula is perhaps connected with the internal motions of the gas. As shown by the observations, the power of the emission sources differs by some hundred times in different points of the amorphous mass (“wisps” and other details). Oort and Walraven believe the “wisps” to be condensations of relativistic electrons ejected from the central star. However, there are some other variable details elsewhere in the nebula (as described by Lampland, and Oort and Walraven).

Oort and Walraven's hypothesis met some important difficulties: (a) the direction of the magnetic lines in this region of the nebula is perpendicular to the wisp's velocity; (b) the dimension of the wisp is about three light months, while it appears during a month and faster, so that the relativistic electrons moving along the lines of force have no time to spread along the wisp; and (c) if the strength is not changing, the energy of the relativistic electrons in the wisp must be some hundred times greater than the density of the magnetic energy, consequently the field strength must grow in the wisp to keep the electrons in the volume.