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Simulation for galaxy dynamics

  1. Sep 30, 2012 #1

    I'm trying to simulate disc galaxy dynamics with a nbody code. The main problem is to get
    good initial values (positions and velocities of each star) in order to reproduce the
    experimental dynamics.

    For the positions, I began by generating a gaussian distribution of stars on 0x and Oy plans ( with mux=muy=0.0 and sigmax != sigmay). On 0z direction, I have generated a uniform distribution whose interval is small compared to sigmax and sigmay. ( this is supposed to reproduce the thin thickness of the disc galaxy). For the velocities of each point, I simply took the newtonian formula :

    vx = - ||vnorm|| * sin(theta)

    vy = ||vnorm|| * cos(theta)

    vz = 0.0

    with ||vnorm||=sqrt(GM/R) with R equal to the distance from the origin and M the mass parameter that we have to adjust.

    Unfortunately, using the code with these initial conditions, the galaxy is not stable from a dynamics point of view.

    I know the model of these conditions is too basic. Could you give me indications to generate initial conditions more accurate, which could reproduce a stable dynamics.

    For example, I should take account of a central bulge.

    Has anyone got some documentation on this problem and models more elaborated ?

  2. jcsd
  3. Oct 9, 2012 #2
    What do you mean by this: for how long should it remain stable, until it develops its spiral arms, or further than that?

    In case you want to make it stable indefinitely, I think you should use some tricks, the most common is to add a massive halo of invisible particles to it.
  4. Oct 10, 2012 #3
    ||vnorm||=sqrt(GM/R) , won't that produce absurd velocities?
    Maybe you could do a velocity dump after so many interactions, to see if they are very high or maxing out.
    Personally I'd use (1+R), or to limit it further, add a terminal velocity as well.
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