The Importance of Physical Models for Deriving Dust Masses and Grain Size Distributions in Supernova Ejecta I: Radiatively Heated Dust in the Crab Nebula

TL;DR

This study models the heating and radiation of dust in the Crab Nebula using a physical approach, revealing more accurate dust masses and grain size distributions than previous simplified models, with implications for understanding supernova contributions to cosmic dust.

Contribution

It introduces a physical model for dust heating and radiation in supernova remnants, providing more precise dust mass and grain size estimates than prior simplified methods.

Findings

Derived dust mass of 0.019-0.13 solar masses depending on composition

Found a power-law grain size distribution with index 3.5-4.0

Dust properties consistent with Type IIP supernovae formation scenarios

Abstract

Recent far-infrared (IR) observations of supernova remnants (SNRs) have revealed significantly large amounts of newly-condensed dust in their ejecta, comparable to the total mass of available refractory elements. The dust masses derived from these observations assume that all the grains of a given species radiate at the same temperature, regardless of the dust heating mechanism or grain radius. In this paper, we derive the dust mass in the ejecta of the Crab Nebula, using a physical model for the heating and radiation from the dust. We adopt a power-law distribution of grain sizes and two different dust compositions (silicates and amorphous carbon), and calculate the heating rate of each dust grain by the radiation from the pulsar wind nebula (PWN). We find that the grains attain a continuous range of temperatures, depending on their size and composition. The total mass derived from the best-fit models to the observed IR spectrum is 0.019-0.13 solar masses, depending on the assumed grain composition. We find that the power-law size distribution of dust grains is characterized by a power-law index of 3.5-4.0 and a maximum grain size larger than 0.1 microns. The grain sizes and composition are consistent with what is expected for dust grains formed in a Type IIP SN. Our derived dust mass is at least a factor of two less than the mass reported in previous studies of the Crab Nebula that assumed more simplified two-temperature models. The results of this study show that a physical model resulting in a realistic distribution of dust temperatures can constrain the dust properties and affect the derived dust masses. Our study may also have important implications for deriving grain properties and mass estimates in other SNRs and for the ultimate question of whether SNe are major sources of dust in the Galactic interstellar medium (ISM) and in external galaxies.