Dusty globules in the Crab Nebula

TL;DR

This study identifies and characterizes 92 dust globules in the Crab Nebula using Hubble data, revealing their properties, motions, and relation to nebular features, and discusses their possible formation mechanisms.

Contribution

It provides the first detailed catalog and analysis of globules in the Crab Nebula, including their physical properties and kinematics, based on high-resolution imaging.

Findings

Globules have radii of 400-2000 AU.

Globules contain a small fraction (~2%) of the nebula's dust mass.

All globules are moving outward with velocities of 60-1600 km/s.

Abstract

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.