AST 402: Stars and Interstellar Medium

3 credits | Prerequisites: AST 301

Course rationale

This is an elective course designed for students majoring in physics, mathematics, engineering or computer science. Students can take it as part of a minor or specialization in astronomy and astrophysics or as a free elective. The course intends to give an overview of the nature, structure and evolution of stars and the composition of the interstellar medium, the nursery of stars.

Course content

Dynamics of binary systems: binary stars and their classification, determining the mass of stars in visual binary systems, eclipsing and spectroscopic binaries. Classification of stellar spectra: formation of spectral lines, spectral types of stars, Maxwell-Boltzmann distribution, Boltzmann and Saha equations, Hertzsprung-Russell diagram. Stellar atmospheres: radiation field; energy density, flux and pressure; stellar opacity, optical depth, radiative transfer, limb darkening, transfer equation, Eddington approximation, spectral line profiles, line broadening. Stellar structure: hydrostatic equilibrium, pressure equation of state, ideal gas law, Fermi-Dirac and Bose-Einstein statistics, stellar energy sources, timescales, quantum tunneling, nucleosynthesis, energy transport and thermodynamics, stellar models and simulation. The Sun: solar interior, solar neutrino problem, solar atmosphere, photosphere, chromosphere, corona, solar wind, the solar cycle, sunspots, solar flares, coronal mass ejections. Interstellar medium: gas and dust in the interstellar medium (ISM), interstellar extinction, Mie theory, hydrogen in the ISM, HI 21-cm radiation, molecular hydrogen, interstellar clouds of different types, interstellar chemistry, heating and cooling of ISM. Star formation: Jeans criterion, homologous collapse, fragmentation of collapsing clouds, formation of protostars, ambipolar diffusion, Hayashi track, pre-main-sequence evolution, brown dwarfs, birth of massive stars, zero-age main-sequence, initial mass function, HII regions, OB associations, T Tauri stars, Herbig-Haro objects, circumstellar disk formation. Stellar evolution: stellar evolution timescales, the main sequence, low-mass main-sequence evolution, Schoenberg-Chandrashekhar limit, high-mass main-sequence evolution, post-main-sequence evolution, subgiant branch, red giant branch, helium flash, horizontal branch, asymptotic giant branch (AGB), AGB evolution, planetary nebulae, clusters of stars, three populations, globular and galactic clusters, color-magnitude diagrams, isochrones and cluster age, Hertzsprung gap. Stellar pulsation: period-luminosity relation, instability strip, period-density relation, Eddington’s thermodynamic heat engine, kappa and gamma mechanisms, partial ionization zones, non-linear hydrodynamic models, nonradial stellar pulsation; p, f and g modes; helioseismology, asteroseismology. Death of massive stars: post-main-sequence evolution of massive stars, luminous blue variables, Wolf-Rayet stars, supernovae, core-collapse supernovae and their remnants, s-process and r-process nucleosynthesis, gamma-ray bursts, cosmic rays. Degenerate remnants of stars: discovery of Sirius B, white dwarfs, pulsating white dwarfs, electron degeneracy, Chandrashekhar limit, cooling of white dwarfs, crystallization, neutron stars, neutron degeneracy, pulsars. Black holes: the general theory of relativity, gravitational redshift and time dilation, worldlines and lightcones, spacetime metric, Schwarzschild metric, orbit of a satellite, a trip into a black hole, mass ranges of black holes, frame dragging, spacetime tunnels, Hawking radiation.

Course objectives

  1. Demonstrate the calculation of stellar mass from observations of binary star systems.
  2. Classify stars based on the spectra of light emitted by them.
  3. Describe the influence of stellar atmospheres on planetary systems.
  4. Derive the equations of stellar structure and use them to construct a model of a star.
  5. Understand the role of interstellar medium as both the nursery and graveyard of stars.
  6. Introduce the theories and observations related to the formation, evolution and death of low, intermediate and high mass stars.
  7. Comprehend the role of modern physics in uncovering the final stages of stellar evolution.


  1. Carroll & Ostlie, An Introduction to Modern Astrophysics, Cambridge University Press, 2017.
  2. Hale Bradt, Astrophysics Processes: The Physics of Astronomical Phenomena, Cambridge University Press, 2008.
  3. Salaris & Cassisi, Evolution of Stars and Stellar Populations, Wiley, 2005.
  4. R. Kippenhahn & A. Weigert, Stellar Structure and Evolution, Springer, 1989.
  5. George W. Collins II, The Fundamentals of Stellar Astrophysics, NASA Astrophysics Data System, 2003.