The Physics of Interstellar Dust

Endrik Krugel

• Publisher: CRC Press
• Year: 2002
• Print ISBN:
  9780750308618
• eBook ISBN:
  9781000687521
• Topic: Physical Sciences
• Subtopic: Astronomy & Astrophysics

Interstellar dust grains catalyse chemical reactions, absorb, scatter, polarise and re-radiate starlight and constitute the building blocks for the formation of planets. Understanding this interstellar component is therefore of primary importance in many areas of astronomy & astrophysics. For example, observers need to understand how dust effects l

Chapter 1

The dielectric permeability

We begin by acquainting ourselves with the polarization of matter. The fundamental quantity describing how an interstellar grain responds to an electromagnetic wave is the dielectric permeability which relates the polarization of matter to the applied field. We recall the basic equations of electrodynamics and outline how plane waves travel in an infinite non-conducting (dielectric) medium and in a plasma. We summarize the properties of harmonic oscillators, including the absorption, scattering and emission of light by individual dipoles. Approximating a solid body by an ensemble of such dipoles (identical harmonic oscillators), we learn how its dielectric permeability changes with frequency. This study is carried out for three scenarios:

• a dielectric medium where the electron clouds oscillate about the atomic nuclei;

• a dielectric medium where the charge distribution in the atomic dipoles is fixed but the dipoles themselves may rotate; and

• a metal where the electrons are free.

1.1 Maxwell’s equations

At the root of all phenomena of classical electrodynamics, such as the interaction of light with interstellar dust, are Maxwell’s formulae. They can be written in different ways and the symbols, their names and meaning are not universal, far from it. Before we exploit Maxwell’s equations, we, therefore, first define the quantities which describe the electromagnetic field.

1.1.1 Electric field and magnetic induction

A charge q traveling with velocity v in a fixed electric field E and a fixed magnetic field of flux density B experiences a force

$F=q\left[E+\frac{1}{c}v\times B\right]$

(1.1)

called the Lorentz force; the cross × denotes the vector product. B is also called the magnetic induction. Equation (1.1) shows what happens mechanically to a charge in an electromagnetic fi...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• 1 The dielectric permeability
• 2 How to evaluate grain cross sections
• 3 Very small and very big particles
• 4 Case studies of Mie calculus
• 5 Particle statistics
• 6 The radiative transition probability
• 7 Structure and composition of dust
• 8 Dust radiation
• 9 Dust and its environment
• 10 Polarization
• 11 Grain alignment
• 12 PAHs and spectral features of dust
• 13 Radiative transport
• 14 Diffuse matter in the Milky Way
• 15 Stars and their formation
• 16 Emission from young stars
• Appendix A Mathematical formulae
• Appendix B List of symbols
• References
• Index