AST80011 (formerly HET617) - Major Project: Computational Astrophysics

Unit Instructor:

A/Prof Jarrod Hurley

Unit Outline:

In this Unit you will obtain a grounding in computer modelling and an appreciation of the ability of science and computers to make complex phenomena understandable. With the aid of numerical experiments, you will learn about specific astrophysical concepts such as the dynamics of the asteroid belt, the evolution of stars and binaries, the orbits of stars within the galaxy, and galaxy dynamics and interactions.

Format of the Unit:

More details about the Unit will be provided in Week 1, but the basic components of this Major Project unit will be:

  1. A major project, chosen from a list of modules - see below - should ideally be chosen by the end of Week 1.
  2. A Scientific Justification, which is to be completed by the end of Week 3. Students must write a 3 page scientific justification of their project, clearly outlining the project aims, objectives and expected outcomes, as well as a detailed timetable of the project for the remainder of the semester. The purpose of the outline is to clearly establish that students understand what they need to do for their project and understand the science behind it. The scientific justification should also include a brief literature review of the subject area.
  3. Newsgroups will be used for general discussions of techniques and problems encountered, as well as for Project Diary postings, whereby students are expected to make brief weekly postings of what they accomplished, learned or tested that week. These submissions will not be marked but are a compulsory part of all Major Project units. Students must submit Project Diary postings in at least 10 of the available weeks throughout the semester (covering both the minor and major project components), otherwise they may receive a fail grade on their final project report. Note also that there is generally less interaction between students in Major Project units as people are working on their own projects.
  4. The Major Project report must be submitted at the end of semester (Week 12). The project report should be about 20 pages or as negotiated with the project supervisor as different types of projects may vary in length substantially.
  5. A final Poster is to be submitted at the end of Week 13, in the style of a non-specialist conference poster. The poster should provide a general overall summary of the project, submitted as a single ppt/pdf poster file or as a maximum of 4 A4 pages (including images), written so as to be able to be understood by your fellow AST80011 students.

Note that Major Project Units, including this one, do not have any associated course content. There is, however, some background science material for each Module.

How It All Works...

In this Unit you will be using pre-existing numerical codes that run on the Swinburne supercomputer via a web interface. Students are not expected to know any programming languages or write their own codes, but they should gain an understanding of the algorithms used in each module. Students will use a web interface to run numerical simulations on the Swinburne supercomputer and can then download the results and data files to analyse on their home computers. This means that you will have to be logged on to the internet to actually run your numerical experiments. Time consuming jobs will be run in a batch mode (which means your job joins a queue), so that students can disconnect from the internet and will be emailed by the webserver once their jobs are complete. Details of how to use the simulators and collect data will be given on each module's homepage.

Data analysis and interpretation is a large part of computational astrophysics, so as well as running lots of experiments, you then need to analyse your data to find out what it all means! Much of the data analysis can be done offline on your local computer using Excel (if using Windows) or Gnuplot (if using Linux). More details about data analysis will also be provided on each module's homepage.


Modules (research areas):

NOTE:

  • Total number of modules available will depend on the number of students enrolled in this unit.


Module 1:Stellar Orbits

Outline:
This Module will focus on stellar orbits and dynamics: the physics of how stars move in a gravitational field. Using the simulator, you will examine:

  • the geometry of ellipses and how to uniquely describe an orbit;
  • the 2-body problem;
  • the 3-body problem; and
  • the motion of stars in a galactic potential.

You will be guided through the module in a step-by-step manner so that you can start to feel comfortable with the idea of a computer model and using the Swinburne simulator. We will first learn about ellipses and elliptic orbits, then examine the time dependence of a two body orbit and learn about orbital binding energy. From here, we will move to the three body problem, starting with the restricted three body problem and moving on to the full three body problem, strengthening our understanding of orbital binding energy, as well as learning about chaotic orbits. Finally we will investigate orbits in a fixed potential to get a feel for individual stellar orbits in a galaxy potential.

You are welcome (and encouraged!) to go off on your own and explore various aspects of stellar orbits as it is an excellent introductory module. However, if you wish to build a project around this module you will need to propose a suitable topic that extends the basic material provided in the module.


Module 2: Pulsar Population Synthesis

Note: This module has an additional prerequisite - students must have an understanding of probability theory.

Outline:
This Module will focus on the pulsar population and how it evolves in the Galaxy. In particular, students will learn:

  • how an individual pulsar evolves;
  • how neutron stars move around the Galaxy:
  • what is meant by observational selection; and
  • how many pulsars we need to observe in order to prove or disprove certain postulates by observing synthetic populations.
Students will first go through some basic mathematics outlining how a pulsar evolves. Then they will create synthetic populations and "observe" them on the supercomputer. They will learn that what you see is quite different to what is "really there". Students will attempt to derive the pulsar birthrate, and ultimately how many millisecond pulsars you need to definitively guarantee that they are as ancient as we believe.


Module 3: Binary Evolution

Note: This module has an additional prerequisite of AST80016 (formerly HET611).

Outline:
In this Module, you will study the interaction of stars in close binary systems. Students will choose a particular type of exotic star or binary, e.g. cataclysmic variables, blue stragglers or black-hole X-ray binaries, and investigate formation pathways using an existing binary evolution code. The dependence of evolution outcomes on particular choices for uncertain parameters will be explored, including how this affects predicted formation rates. Results can then be compared to observations, i.e. population synthesis. In the process of this study, students will learn about the physics of close binary systems and how this causes the appearance of stars to deviate from the predictions of standard stellar evolution. Stellar evolution and stellar populations of star clusters can also be explored within this module.


Module 4: Galaxy Interactions

Outline:
In this Module, you will run N-body simulations to investigate the dynamics of galaxy interactions and galactic mergers. You will need to set up the initial configuration of the two galaxies (by varying a range of parameters) so that you can run a series of numerical experiments. For example, you may wish to study the gravitational interactions between large spiral galaxies and smaller satellite galaxies to study the destruction of the satellite galaxy and the formation of bridges and tidal tails.

There are three main aspects to this Module:

  • to gain a basic understanding of the equations that govern the system (without attempting to solve them!) You should be able to write down an algorithm for merging two galaxies;
  • to experiment with the parameters (such as galaxy mass ratios and impact parameter) to try and produce a galaxy merger, and explain why the resulting systems do - or do not - merge; and
  • to understand the concept of a numerical model and learn how to perform and analyse numerical experiments.


Module 5: Solar System Dynamics

Note: This module has an additional prerequisite of AST80005 (formerly HET602).

Outline:
In this Module you will investigate gravitational N-body interactions by studying the dynamics of the Solar System. Using the simulator, you will be able to study a number of different systems, such as a swarm of asteroids or planetesimals in the presence of planets (or protoplanets) in order to study gravitational scattering and resonances, or the dynamics of Saturn's ring and satellite system.

We will help start you off by stepping you through some suggested systems, including:

  • a very simple planetary system: the Earth and the Sun. You can investigate how the system evolves when you add different sets of test particles (i.e. an asteroid belt), and in particular examine the effect of the initial physical properties of the test particles in the evolution of the whole system;
  • the Solar System: you can study how a system's evolution depends on the simulation parameters, rather than the initial physical properties of the test particles and planets; and
  • the Not-So-Very Solar System: you can also study the evolution of planetary systems that are not like our own, exploring the dynamics of the newly discovered extrasolar planet, or some fictitious system not yet discovered!

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