Tools of Astrophysics-Topical (PHY445.5)

Venue:  Chern Lecture Hall on Tuesdays and Feynman Lecture Hall on Fridays

Class Timings: Tuesdays and Fridays from 1:45 PM - 3:15 PM

First Meeting: 06 January 2026 (Tuesday)

Prerequisites: Classical mechanics, Electromagnetism, Introductory GR (helpful but not essential), differential equations. 

Description: 

This course aims to survey astrophysical phenomena across a wide range of scales — starting from the Hubble scale of the universe to the event horizons of black holes. We will emphasise a physics-first approach, focussing on the tools, approximations, and dynamical principles that recur across regimes. 

Topics: 

  • Setting the stage: Why gravity dominates astrophysics, Scale invariance and dimensional analysis, Time scales — dynamical, free-fall and relaxation, Hierarchies in mass, length and time
  • Cosmology: Cosmological Principle, FRW metric, Friedmann equations, Expansion vs structure growth, Linear perturbation theory, Jeans instability, Power spectra, Spherical collapse, Press-Schechter formalism, Halo mass function. 
  • Galaxies: Collisionless Boltzmann equation, Virialization, Rotation curves, disk stability, Star formation, Jeans mass and fragmentation, Initial Mass Function. Stellar clusters, Two-body relaxation, Mass segregation, Evaporation. 
  • Stars:  Hydrostatic equilibrium, Equations of stellar structure, Polytropes and scaling relations, Stellar evolution, Binary evolution, Gravitational collapse and supernovae. 
  • Compact objects: Electron degeneracy pressure, Chandrasekhar limit, Structure of white dwarfs, Mass-radius relation. TOV equations, Structure of neutron stars, Mass-radius relation. Schwarzschild solution, Particle and photon orbits in Schwarzschild geometry, Astrophysical black holes, Accretion physics, Compact binary coalescences. 

Evaluation:  70% on homework, 30% on final project 

References (not exclusive): 

  • Arnab Rai Choudhuri, Astrophysics for Physicists (Cambridge; 2010). 
  • T. Padmanabhan, Theoretical Astrophysics (Cambridge 2001). 
  • James Binney and Scott Tremaine, Galactic Dynamics (Princeton, 2008). 
  • Saul Teukolsky and Stuart L. Shapiro. Black Holes, White Dwarfs and Neutron Stars: The Physics of Compact Objects (Wiley-VCH; 1983).