Astronomy 320: Spring 2020

Theoretical Astrophysics

1st galaxies: gas density (Ricotti, Parry & Gnedin 2016) 

Modern astronomy has its roots firmly grounded in the fundamental principles of physics (both classical and quantum). Furthermore, many branches of physics as we know them today trace their origins to the search for universal physical laws to explain natural phenomena discovered and analyzed by astronomers.

The goal of theoretical astrophysics is to provide physical and conceptual understanding of the diverse systems that represent our universe. Introductory astronomy courses are often organized by scale (planets, stars, galaxies and the universe as a whole) and observational astronomy courses are often organized by wavelength because of the different technologies. To emphasize the different approach needed for developing a theoretical framework, this course is organized into themes of governing physical principles. For each of the three main themes (gravity, gas physics and quantum physics), we start with fundamental principles and then discuss applications in various astronomical contexts. We will also discuss systems in which several principles interact synergistically and demonstrate how astrophysical theories are developed by successive model refinements and confrontation with data. We will show how application of simple physical laws can explain the observed properties of an astounding range of astronomical objects!

I will assume a basic knowledge of astronomical concepts (up to the ASTR120/ASTR121 level) as well as basic physics (up to the PHYS270/PHYS271/PHYS273 level)


    Instructor:  		Massimo Ricotti
    Class:       		AJC 2134
    Lectures:    		Tuesday and Thursday from 11:00pm to 12:15pm
    First class: 		Tue Jan 28 
    Last  class: 		Tue May 12 
    TA:		 		Alexander Dittmann 
    Reading session (w/Alex):	Wednesday from 1:00pm to 1:50pm (ATL 2428)
    First reading session: 	Wed Jan 29

What's New?

Jan 28: First class
Jan 29: Reading session (introduction of Alex Dittmann)

Contact info and Notes

Course Outline

The Syllabus is available on ELMS and here PDF format.


GRAVITY (notes)
#1Jan 28 Introduction; Recap of Newton’s laws and the conservation of momentum
#2Jan 30 Newtonian gravity
#3Feb 4 One body problem - conservation laws and constants of motion
#4Feb 6 One body problem - solving the equation of motion
#5Feb 11 One body problem - derivation of Kepler's Laws
#6Feb 13 One body problem - cont.
#7Feb 18 Two-body problems and binary systems (notes)
#8Feb 20 In class execise: LOS velocity and mass function
#9Feb 25 Two + one (restricted three) body problem - Lagrange points
#10Feb 27 Two + one (restricted three) body problem - Effective potential
#11Mar 3 In class exercise: Lagrange L3
#12Mar 5 N-body dynamics - the virial theorem
- Mar 10 MIDTERM (in class)
#13Mar 12 N-body dynamics - applications of the virial theorem Pressure and the concept of hydrostatic equilibrium
#14Mar 24 Covid-19 (classes cancelled)
#15Mar 26 Covid-19 (classes cancelled)
#16Mar 31 Pressure and the concept of hydrostatic equilibrium (ONLINE)
#17Apr 2 Atmospheres in an external gravitational field (ONLINE)
#18Apr 7 Self-gravitating atmospheres (ONLINE)
#19Apr 9 Introduction to thermodynamics and statistical mechanics (ONLINE)
#20Apr 14 Statistical mechanics of ideal gas (ONLINE)
#21Apr 16 Radiation gases (ONLINE)
#22Apr 21 Radiation gases (cont) and applications to Cosmology (ONLINE)
#23Apr 23 Brief introduction to hydrodynamics (ONLINE)
#24Apr 28 The Bohr model of the atom
#25Apr 30 Particle wave duality and particle in a box (ONLINE)
#26May 5 Fermions and bosons; Fermi-Dirac and Bose-Einstein statistics (ONLINE)
#27May 7 Degeneracy pressure and while dwarf (ONLINE)
#28May 12 Type-1a supernovae and neutron stars (ONLINE)
-May 14 Final exam (format and time TBD)


No textbooks are required for this course.
I will use my own class notes that I will hand out and are available for download on ELMS. Since the course is organized by topics, there are no textbooks that follow the structure of this course. You can find some of the topics that will be covered in introductory astrophysics texts. Two of them, on which you may find some useful material are the following:
  • Astrophysics for Physicists, by Arnab Rai Choudhuri,
    (Cambridge University Press, 2010) ISBN-13: 978-0521815536
  • Astrophysics in a Nutshell, by Dan Maoz,
    (Princeton University Press, 2007) ISBN-13: 978-0691125848
These books are merely listed for your convenience, but you do not need to buy either of them. In addition a lot of useful material can be found on the web, including Wikipedia. However, keep in mind that some of the derivations or homework you will be exposed to in this class, are meant to introduce you to research in astrophysics and problem solving, so you will not find all the answers on books or on the web.

Course Grading

  • Class participation 10%
  • Homework 30%
  • Midterm exam 25%
  • Final exam 35%
Letter grades will be assigned guided by the following scheme.
  • A 100% - 90%
  • B 89.9% - 80%
  • C 79.9% - 70%
  • D 69.9% - 60%
  • F below 60%
I will also adopt the finer division of the letter grades using pluses and minuses.


Homework will be assigned every week or every other week (total of 6 homework). Their due dates will be announced at the time they are assigned. On the due date the students will be expected to turn in their homework in class. The homework turned in will be graded and returned to the students. I will provide solutions and discuss them in class.

I will post the HOMEWORK and solutions on ELMS

Wiki pages related to class's discussions

Class #1
Class #2
Discussion Section #7
Class #8
Class #9
Class #24 and #25