Disks and Accretion

Course manual 2025/2026

Course content

Accretion is the process by which stars and planets form and – when the central object is a black hole or neutron star – is the most efficient energy source in the universe. The energy is released as electromagnetic radiation with unique observational signatures and via powerful outflows and jets. In this course we will study the physics of accretion flows and learn about the different types of accreting objects and how their properties are interconnected by the accretion process, from stellar-mass black holes and neutron stars in binary systems, over young stars to the accreting supermassive black holes in active galactic nuclei. We will see how the observed properties of these extraordinary objects can be explained by accretion theory, and how the observations have also led to major advances in our understanding of the theory. The course will consist of lectures combined with general principles- and problem-solving tutorials and have a computing project part, aiming to provide a wide physical understanding and to train problem solving abilities related to accretion phenomena.

Study materials

Literature

• Frank, King and Rayne: 'Accretion Power in Astrophysics'

Syllabus

• Extensive course notes on the core material

Other

• Supplementary notes and research papers

Objectives

• Explain and apply general physical principles of accretion.
• Distinguish the characteristic physical processes in various accreting astrophysical systems.
• Interpret observational data in terms of accretion theory.
• Use the thin disk approximation to analytically connect physical quantities.
• List and explain the assumptions underlying analytic approaches.
• Critically reflect on their validity for a given system.
• Write Python codes to solve time dependent problems that cannot be tackled analytically.

Teaching methods

• Lecture
• Self-study
• Computer lab session/practical training

The course spans seven weeks with two lectures per week, Mondays and Wednesdays. In these sessions which will be in a classical lecture style, we will cover the background material and introduce all relevant physical concepts, if possible by looking at relevant examples. In addition to the lectures, there are two kinds of tutorial sessions: one on general principles and one on problem solving. Every week you will prepare a few homework assignments for the problem solving tutorials on Wednesdays. In the computing mini-project, step by step, you will learn how to use and extend a python package called DISKLAB to solve 1D time-dependent accretion problems and analyze disk structure, stability, emission and variability properties of the solutions. We will use Jupyter notebooks and you will add new physical processes to the existing toolkit. Seeing the fluid equations discussed in the lecture ‘in action’ will help develop your understanding for the accretion problem.

Learning activities

Attendance

Additional requirements for this course:

• The student may be absent in one out of six problem solving classes without impacting their grade.

Assessment

15% of the final grade will be due to graded homework assignments providing formative assessment.
20% of the final grade will be due to the computing project report.
5% of the final grade will depend on the quality of your peer assessment.
60% of the final grade will be due to the summative examination. 

You will be allowed a cheat-sheet during the final exam.  The resit might be offered as oral exam if all parties agree to this. 

Assignments

General principles assignments (non-graded): During the tutorial, we will hand out “Questions of the week” covering the key concepts of the preceeding week. You will be given ample time to check your notes and answer on your own. Then we will discuss the topics with the group and the lecturer, making sure everyone understands what was covered in the lecture providing feedback. These questions will be similar to “part A” questions in the exam.

Problem solving (graded): in preparation for the tutorial, you will work on a few “exam level” problem sets as individual homework. You need to bring your answers to next weeks Thursday tutorial. For the homework assignments, you will pair up with another student during the Thursday tutorial (the pairing will be done randomly by us and will be different for each tutorial) and then grade and discuss each other’s solutions. The TA will then collect and control your checked problem sets again to determine your grades for the problem set. The solutions thus checked and annotated by your peer and the TA will be returned back to you as feedback. We don’t hand out master solutions, so you need to make sure you go out of the tutorial knowing whats the right solution!

A note on (peer-assessment) grading: The TA will have the last word on the grade, so it does not pay off to e.g. give full marks for sloppy solutions. As grader, you need to annotate the problem set so its clear where you give/deduct points and how it all adds up. Since your answers need to be readable by your peers, we reserve the right to deduct points if your notes are unreadable or ambiguous in some other way. You will also get points for good grading (on a scale of 0-2): every time you grade a problem set it accounts to 1% of the final grade. You will be awarded one point if you made a reasonable attempt but can still improve (as per the criteria listed above) and two points if your grading was spot on. We will take your best 5 gradings (out of six) which count 5% towards your final grade.

There will be six problem sets and we will take your best 5 sets contributing 20% towards your final grade. It really pays off to carefully complete the homework as the final “part B” exam questions will be oriented similarly.

Computing mini project (graded report): in the Tuesday workshops we will introduce the methods and you will have some time to work on your mini-project. The lecturer will be there to help you when you are stuck. It is expected that you’ll also need to work on the project at home. As final project report, you should submit your executable and thoroughly annotated Jupyter notebooks and your modified DISKLAB code.

For each part, marks will be given out of 5, under the following scheme:

• 0-3 marks for not achieving the basic plot/result requested. The maximum 3 marks can be obtained by not achieving but making a good attempt, e.g. with some explanation of what went wrong and what result might be expected. A (running) program that shows an honest attempt but does not obtain the correct result can still be awarded 1 mark if it is well documented (commented).

• 3 marks for following and achieving the basic plot/result requested, including at least a basic (descriptive) explanation

• 4 marks for following and achieving the basic plot/result requested, with good presentation of the results and accurate discussion on how the results connect to the theory learned in the course.

• 5 marks for achieving the results expected and going significantly beyond, e.g. further demonstration of some of the relevant accretion physics using the code.

Fraud and plagiarism

The 'Regulations governing fraud and plagiarism for UvA students' applies to this course. This will be monitored carefully. Upon suspicion of fraud or plagiarism the Examinations Board of the programme will be informed. For the 'Regulations governing fraud and plagiarism for UvA students' see: www.student.uva.nl

Course structure

Additional information

Recommended prior knowledge: Physics and astrophysics at the Bachelor level.

Contact information

Coordinator

• dr. Oliver Porth

Staff

• S. Praharadj