# Astronomy 320: Spring 2021

# Theoretical Astrophysics

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)

#### Schedule

Instructor: Massimo Ricotti Class: Online Lectures: Tuesday and Thursday from 11:00pm to 12:15pm First class: Tue Jan 26 Last class: Tue May 11 TA: Harrison Agrusa Reading session (w/Harrison): Wednesday from 1:00pm to 1:50pm (online) First reading session: Wed Feb 3

#### What's New?

Jan 26: First class |

Feb 3: Reading session (introduction of Harrison Agrusa) |

#### Contact info and Notes

- Office: Physical Sciences Complex (PSC) 1156
- E-mail: ricotti "at" astro "dot" umd "dot" edu
- Phone: (301) 405 5097
- Office hours: TBD
- Class web page: http://www.astro.umd.edu/~ricotti/NEWWEB/teaching/ASTR320_21.html
- TA: Harrison Agrusa
- Office: PSC
- E-mail: hagrusa "at" astro "dot" umd "dot" edu
- Office hours: TBD

#### Course Outline

The Syllabus is available on ELMS and here PDF format.

Date | Lecture | |
---|---|---|

GRAVITY (notes) | ||

#1 | Jan 26 | Introduction; Recap of Newtonâ€™s laws and the conservation of momentum |

#2 | Jan 28 | Newtonian gravity |

#3 | Feb 2 | One body problem - conservation laws and constants of motion |

#4 | Feb 4 | One body problem - solving the equation of motion |

#5 | Feb 9 | One body problem - derivation of Kepler's Laws |

#6 | Feb 11 | One body problem - cont. |

#7 | Feb 16 | Two-body problems and binary systems (notes) |

#8 | Feb 18 | In class execise: LOS velocity and mass function |

#9 | Feb 23 | Two + one (restricted three) body problem - Lagrange points |

#10 | Feb 25 | Two + one (restricted three) body problem - Effective potential |

#11 | Mar 2 | In class exercise: Lagrange L3 |

#12 | Mar 4 | N-body dynamics - the virial theorem |

#13 | Mar 9 | N-body dynamics - applications of the virial theorem Pressure and the concept of hydrostatic equilibrium |

- | Mar 11 | MIDTERM (in class) |

- | Mar 16 | SPRING BREAK |

- | Mar 18 | SPRING BREAK |

#14 | Mar 23 | N-body dynamics - two body relaxation |

GAS PHYSICS (notes) | ||

#15 | Mar 25 | Pressure and the concept of hydrostatic equilibrium |

#16 | Mar 30 | Atmospheres in an external gravitational field |

#17 | Apr 1 | Self-gravitating atmospheres |

#18 | Apr 6 | Introduction to thermodynamics and statistical mechanics |

#19 | Apr 8 | Statistical mechanics of ideal gas |

#20 | Apr 13 | Radiation gases |

#21 | Apr 15 | Radiation gases (cont) and applications to Cosmology |

#22 | Apr 20 | Brief introduction to hydrodynamics |

QUANTUM PHYSICS (notes) | ||

#23 | Apr 22 | The Bohr model of the atom |

#24 | Apr 27 | Particle wave duality and particle in a box |

#25 | Apr 29 | Fermions and bosons; Fermi-Dirac and Bose-Einstein statistics |

#26 | May 4 | Degeneracy pressure and while dwarf |

#27 | May 6 | Type-1a supernovae and neutron stars |

#28 | May 11 | Review |

- | May 13 | Final exam (format and time TBD) |

#### Textbooks

- 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.
- Online participation/Quizzes 25%
- Homework 25%
- Midterm exam 25%
- Final exam 25%
- A 100% - 90%
- B 89.9% - 80%
- C 79.9% - 70%
- D 69.9% - 60%
- F below 60%
- Problem related to perturbation theory (Bungee Cord) Note: we skipped perturbation theory in class, hence this topic will NOT be on the Midterm or Final

#### Course Grading

#### Homework

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 |