This book is based on a series of lectures for an Astrophysics of the Interstellar Medium (ISM) master’s degree in Astrophysics and Cosmology at Padova University. From the cold molecular phase in which stars and planetary systems form, to the very hot coronal gas that surrounds galaxies and galaxy clusters, the ISM is everywhere. Studying its properties is vital for the exploration of virtually any field in astronomy and cosmology. These notes give the student a coherent and accurate mathematical and physical approach, with continuous references to the real ISM in galaxies. The book is divided into three parts. Part One introduces the equations of fluid dynamics for a system at rest and acoustic waves, and then explores the real ISM through the role of thermal conduction and viscosity, concluding with a discussion of shock waves and turbulence. In Part Two, the electromagnetic field is switched on and its role in modulating shock waves and contrasting gravity is studied. Part Three describes dust and its properties, followed by the main stellar sources of energy. The last two chapters respectively address the various components of the ISM and molecular clouds and star formation.
Author(s): Giovanni Carraro
Series: UNITEXT for Physics
Edition: 1
Publisher: Springer Nature Switzerland
Year: 2021
Language: English
Pages: 356
City: Cham, Switzerland
Tags: fluid dynamics, accoustic waves, interstellar medium, shock waves, turbulence, plasma, dust, stellar winds, star formation
Preface
Contents
1 Fundamental Equations for Ideal Fluids
1.1 Introduction: Fluids as Continuous Systems
1.2 Continuity Equation
1.3 Volume Forces and Surface Forces. Stresses
1.4 Equation of Motion (Euler Equation) for Ideal Fluids
1.5 Conservation of Total Energy and Thermal Energy
1.6 Vorticity in Ideal Fluids. Potential Motion
1.7 Numerical Solutions of Hydrodynamical Equations
1.8 Synthetic Summary
2 Acoustic Waves
2.1 Acoustic Waves in an Ideal Fluid at Rest
2.2 Velocity of Propagation in a Dispersive Medium
2.3 Acoustic Waves in a Patchy Medium at Rest
2.4 Acoustic Waves in a Gravity-Dominated Medium
2.5 Virial Theorem
2.6 Gravitational Collapse of a Sphere
2.7 Synthetic Summary
References
3 Real Fluids
3.1 Transport Phenomena
3.2 Thermal Conduction
3.3 Internal Friction
3.4 Navier–Stokes Equation
3.5 Energy Dissipation by Internal Friction
3.6 Energy Balance in a Real Fluid
3.7 Integration of Equations for a Real Fluid
3.8 Case of Fluid with Low Viscosity
3.9 Similar Motions
3.10 Synthetic Summary
References
4 The Interstellar Medium
4.1 Thermal Balance of Interstellar Gas
4.2 Thermodynamic State of Interstellar Gas
4.3 Cooling Processes
4.4 Heating Processes
4.5 Thermal Instability
4.6 Synthetic Summary
References
5 Shock Waves
5.1 Supersonic Motion and Discontinuity
5.2 Jump Conditions
5.3 Shock Waves
5.4 Rankine–Hugoniot Conditions for an Ideal Gas
5.5 Shock Waves in the Interstellar Medium
5.6 Isothermal Shock: Schematic Discussion
5.7 Structure of the Relaxation Layer
5.8 Observability of Radiative Shocks
5.9 Synthetic Summary
Reference
6 Turbulence
6.1 Experimental Aspects of Turbulence
6.2 Stability of Stationary Motion and Turbulence Onset
6.3 Notes on the Statistical Description of Turbulence
6.4 General Characteristics of Turbulence
6.5 Kolmogorov's Theory
6.6 Turbulence of the Interstellar Medium
6.7 Synthetic Summary
References
7 Electrodynamics and Magnetohydrodynamics
7.1 Plasmas. Debye Screening Length
7.2 Plasma Oscillations
7.3 A Note on Systems of Measurement Units
7.4 Maxwell's Equations
7.5 Magnetic Field Equation
7.6 Freezing of the Magnetic Field Lines of Force
7.7 The Galactic Magnetic Field: Origin and Methods of Measure
7.8 Synthetic Summary
8 Motion of a Plasma in a Magnetic Field
8.1 Expressions of Magnetic Force
8.2 Fundamental Equations of Magnetohydrodynamics
8.3 Motion of a Plasma with Respect to Magnetic Lines of Force
8.4 Virial Theorem
8.5 Application of the Virial Theorem
8.6 Ambipolar Diffusion
8.7 Synthetic Summary
9 Magnetohydrodynamic Waves
9.1 Classification of MHD Waves
9.2 Alfven Waves
9.3 MHD Waves: General Discussion
9.4 MHD Waves with Generic Propagation Direction
9.5 Waves with Particular Direction of Propagation
9.6 Alfven Waves Attenuation
9.7 Excitation of MHD Waves
9.8 Magnetohydrodynamic Shock Waves
9.9 Synthetic Summary
10 Dust from the Interstellar Medium
10.1 Introduction
10.2 The Extinction of Radiation
10.3 Observational Determination of Stellar Extinction
10.4 The Extinction Curve of the Diffuse Medium in the Galaxy
10.5 Methods for Determining RV
10.6 The Equilibrium Temperature of the Grains
10.7 The Temperature of the Small Grains
10.8 IR Emission of Galaxies
10.9 Synthetic Summary
11 HII Regions
11.1 Introduction
11.2 Ionisation Balance
11.3 Energy Balance and Temperature of an HII Region
11.4 The Strömgren Sphere
11.5 Effect of Dust on the HII Region
11.6 Evolution of the HII Region in a Homogeneous Medium
11.7 Classification of Ionization Fronts
11.8 HII Region Expansion
11.9 End of Expansion
11.10 Expansion of an HII Region in an In-Homogeneous Medium
11.11 Radio Frequency Emission
11.12 Infrared Emission
11.13 Calculation of the Lines of the Balmer Series
11.14 HII Regions Excited by a Cluster
11.15 Synthetic Summary
Reference
12 Stellar Winds
12.1 Introduction
12.2 Classification of Winds
12.3 Structure and Evolution of a Bubble Produced by a Strong Wind
12.4 A Simplified Model for the Radiative Phase
12.5 Evolution in Phase D
12.6 Observations of the Bubbles
12.7 Evolution of the Bubble in an In-Homogeneous Medium
12.8 Synthetic Summary
References
13 Supernovae Remnants
13.1 Supernovae
13.2 SNR Evolution
13.2.1 Expansion End
13.3 Expansion of a SNR in a Patchy Medium
13.3.1 Magnetic Field
13.3.2 Relativistic Particles
13.3.3 Spherical Symmetry
13.4 Models of Evolution in a Patchy Medium
13.5 Effects of a SNR on the Interstellar Medium
13.6 Superbubbles and Supershells
13.7 Description of some SNRs
13.8 Synthetic Summary
References
14 The Interstellar Medium and Its Components
14.1 The Structure of the Interstellar Medium
14.2 Neutral Gas Diagnostic Techniques: The Line at 21 cm
14.3 The Spiral Structure of the Milky Way
14.4 Ionized Gas Diagnostic Techniques
14.4.1 Dispersion of Pulsar Signals
14.4.2 Recombination Optical Emission
14.4.3 Absorption at Low Radio Frequencies
14.5 The Hot Component: Coronal Gas
14.6 The Cold Neutral Component: The Clouds of HI.
14.7 The Warm Neutral Component
14.8 Synthetic Summary
References
15 Molecular Clouds
15.1 Detection of Molecular Gas
15.2 Correlation Between CO Emission and Molecular Gas Mass
15.3 The Distribution of H2 in the Galaxy
15.4 Distribution of H2 in Other Galaxies
15.5 Clouds Classification and Statistical Properties
15.6 Mechanical Equilibrium of Molecular Clouds
15.7 Why the Clouds Where Stars Form Are Molecular?
15.8 Mechanisms of Molecular Cloud Formation
15.8.1 Formation of Clouds by the Compression of Ambient Gas Induced by Shock Waves
15.8.2 Cloud Formation by Agglomeration of Smaller Clouds.
15.8.3 Cloud Formation Through Medium Instability
15.8.4 Summary
15.9 Synthetic Summary
References
16 Star Formation
16.1 Observational Data Related to Star Formation
16.2 Star Formation in the Presence of a Magnetic Field
16.3 The formation of Low-Mass Stars
16.4 Low-Mass Star Formation Scenario
16.5 Observational Findings
16.6 Synthetic Summary
