Dark Matter Halos and N-body Simulations
Hey just got done with some research. I’m doing a short review of modelling methods of Dark Matter Halos (DMHs). DMHs may account for up to 95% of a galaxy’s mass, making them a crucial component of our universe. Dark matter , however, does not interact with electromagnetic radiation and is invisible. Thus, it’s only evidence comes from gravitational observations seen between large-scale objects in the universe. DMHs are believed to consist of weakly-interacting massive particles (WIMPs) and/or massive compact Halo objects (MACHOs). It is essential to construct models of DMHs that account for current observations in order to predict other observable consequences.
N-body simulations are simply simulations of N particles and their interactions. There are a large number of types of N-body simulations, including but not limited to Particle-Particle, Particle-Mesh, Nested Grid Particle-Mesh, Fast-Multipole-Method, and Self-Consistent Field. These different types assume different interactional components and utilize different calculational methods. For example, in Particle-Particle N-body simulations a computational device (usually a computer cluster) will calculate the gravitational forces between a number of particles and then integrate the resultant expressions to find positions and velocities of the particles. In Particle-Mesh simulations, the force is treated as a field quantity, which is approximated on a series of discrete intervals – a mesh. The field potential equation is solved, and the force field calculated from this is then interpolated on the grid to find forces on the particles. These forces are then integrated to find positions and velocities of the particles. While this method may be faster than the particle-particle method, it is only useful for calculating particles that are relatively distant from each other and distributed relatively uniformly. This is because the mesh is approximating these particles as non-discrete objects.
Amara Grap’s site on N-body simulations has other types, which all have their own pros and cons.
One of my favorite, and most influential, simulations was done by Navarro, Frenk, and White in 1996 (The Structure of Cold Dark Matter Halos). They simulated the formation of 19 different systems, with masses ranging from those of dwarf galaxies to those of rich clusters. While very successful, they were able to discern two shortcomings of the (then) current CDM model: “CDM halos are too concentrated to be consistent with the halo parameters inferred for dwarf irregulars, and the predicted abundance of galaxy halos is larger than the observed abundance of galaxies.” This set of simulations set the stage for a large variety of future N-body simulations of cold dark matter halos, from which most properties of the beasts have been derived.
This entry was posted on Friday, November 28th, 2008 at 2:34 am and is filed under Astrophysics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
