Resolution of Crab nebula filaments into chains of quasistellar knots

Abstract

We have clearly resolved a number of the Hα emitting filaments in the Crab nebula into chains of knots with diameters ≲1.0 arc s. This resolution was possible because sub-arcsecond seeing is common on Mauna Kea, Hawaii (altitude 4,204 m) but quite rare at the sites of other large telescopes situated at lower altitudes. Individual filaments resemble beads on a string which shows that these objects are rope-like structures. In the brightest filament close to the Crab pulsar the quasistellar knots are slightly displaced from the spine of the low-density filament on which they are superposed. This segregation might be understood if the dense knots have been accelerated outwards by a lesser amount than the low-density filament in which they were originally embedded. The present results show that a substantial fraction of the line emission of the Crab nebula originates in the small and very dense quasi-stellar knots that lie along the spines of filaments. This will affect estimates of the mass and composition of the Crab nebula, and observations of the motions of quasistellar knots should enable one to study the expansion (and eventually perhaps even the acceleration) of the Crab nebula with much greater precision than was possible previously.