CMP-project3

N-body simulation of galaxy merger

This is the public repository for the code of N-body simulation of galaxy merger. This code can set initial positions and velocities of galaxy(contained disk and bulge) following a Kuzmin's disk potential and a Hernquist's bulge potential. The acceleration for each time step is calculated by using octree method and using leap frog algorithm to update the position and velocity for each particles. This can be use to analyse the following properties of one single galaxy:

• 2D animation of one self-evolved single galaxy
• Energy plot of the system

And it can also be used to simulate the merger of two galaxies and analyse the following properties:

• 2D animation of two galaxies merger
• Energy plot of the system
• Separation plot of the center of mass

We also provide you a specific case, to simulate the merger of Milky Way and Andromeda.

Installation

Now this code can be worked on Windows system. Before installation, make sure your system meets the prerequisites listed in Dependencies, list below.
To install, there are two ways:

1. Download this repository
   You can go to our github page to download it and save it on your machine
2. Clone this repository
   Clone it on your machine:

git clone https://github.com/boson112358/cmp-project

Dependencies

The code requires the following(some of the functionality might work with older versions):

• Python version 3.9+
• argparse >= 1.4.0
• matplotlib >= 3.3.4
• numpy >= 1.20.1
• tqdm >= 4.59.0

Running

1. Simulating one single galaxy

First, we can use this code to generate one single galaxy contained disk and bulge. By running testSingleGalaxy.py, it can generate the animation of given timestep, the plot of number of force calculation, the initial position distribution of galaxy in xy plane and the particle's trajectory plot. You can find the plot in the folder ./plot. In our repository, we provide you a bat profile runSingleGalaxy.bat with some arguments. You can change the corresponding arguments to get the self-evolved single galaxy you want. For this simulation, you can use the following arguments: Particle_Number, Step, Length, Multiple_Mass, Energy_Tracking. For the initial condition quantities you set, you can find it in the folder ./data, named output.txt.

python testSingleGalaxy.py --Particle_Number 200 --Step 200 --Multiple_Mass 2

2. Simulating two galaxies merger

Second, we can use this code to simulate merger of two galaxies. By running testMergerTwoGalaxy.py, it can generate the animation of given timestep, the plot of number of force calculation, the initial position distribution of galaxies in xy plane, the particle's trajectory plot and the separation distance of center of mass plot. You can find the plot in the folder ./plot. In our repository, we provide you a bat profile runMergerTwoGalaxy.bat with some arguments. You can change the corresponding arguments to get the merger senario you want. For this simulation, you can use the following arguments: Particle_Number, Step, Length, Multiple_Mass, Mass_Ratio, Energy_Tracking. For the initial condition quantities you set, you can find it in the folder ./data, named output.txt.

python testMergerTwoGalaxy.py --Particle_Number 100 --Step 100 --Mass_Ratio 1.35

What's more, now in our code, we only set the two galaxies with a distance of 20 units in x-axis, we encourage you to set the initial postions and velocities in the profile testMergerTwoGalaxy.py, to change the following two lines(the last six parameters is (x,y,z,vx,vy,vz)):

galaxy1 = make_galaxy(N1d, M1d, N1b, M1b, -10, 0, 0, 0, 0, 0)
galaxy2 = make_galaxy(N2d, M2d, N2b, M2b, 10, 0, 0, 0, 0, 0)

3. Simulating the Milky Way and Andromeda merger

Third, we can use this code to simulate merger of Milky Way and Andromeda. We set the initial positions and velocities for Milky Way and Andromeda merger. By running runMWandM31.py, it can generate the animation of given timestep, the plot of number of force calculation, the initial position distribution of galaxies in xy plane, the particle's trajectory plot and the separation distance of center of mass plot. You can find the plot in the folder ./plot. In our repository, we provide you a bat profile runMWandM31.bat with some arguments. You can change the corresponding arguments to get the merger senario you want. For this simulation, you can use the following arguments: Particle_Number, Step, Length, Multiple_Mass, Energy_Tracking. For the initial condition quantities you set, you can find it in the folder ./data, named output.txt.

python testMWandM31.py --Particle_Number 200 --Step 200 --Length 200 --Multiple_Mass 4

The following is the explaination of argument.

1. --Particle_Number
   Set the initial bulge particle number for one single galaxy, for the disk, it's 3 times of the bulge number. The default value is 100.
2. --Step
   Set the step for simulation, for one step, it can be scaled to 10 Myr. The default value is 100.
3. --Length
   Set the length of the box, we encourage you to set a bigger length to avoid periodic boundary. The default value is 100.
4. --Multiple_Mass
   Set the mass condition for galaxy. Now for every single galaxy, we set the total mass is 4/3, which can be scaled to 7.4x10^10 solar mass, you can set the Nfold mass for galaxy. The default value is 1.
5. --Energy_Tracking
   Turn on the Energy Tracking. You can get the energy plot for the simulation, but it may slower the simulation.
6. --Mass_Ratio
   Set the mass ratio of two galaxies. When simulating two galaxies, you can change the mass ratio of two galaxies, which it galaxy2/galaxy1. The default value is 1.

Relevant material

For more detail about our code, you can check out our presentaion slides in this repository.

Authors

• Davey Plugers
• Zhen Xiang