Dusty globules in the Crab Nebula
  From existing broad-band images obtained with the Hubble Space Telescope, we
located 92 globules, for which we derived positions, dimensions, orientations,
extinctions, masses, proper motions, and their distributions. The globules have
mean radii ranging from 400 to 2000 AU and are not resolved in current infrared
images of the nebula. The extinction law for dust grains in these globules
matches a normal interstellar extinction law. Derived masses of dust range from
1 to 60 x 10^(-6) solar masses, and the total mass contained in globules
constitute a fraction of approximately 2% or less of the total dust content of
the nebula. The globules are spread over the outer part of the nebula, and a
fraction of them coincide in position with emission filaments, where we find
elongated globules that are aligned with these filaments. Only 10% of the
globules are coincident in position with the numerous H2-emitting knots found
in previous studies. All globules move outwards from the centre with
transversal velocities of 60 to 1600 km/s, along with the general expansion of
the remnant. We discuss various hypotheses for the formation of globules in the
Crab Nebula.
