How to Convert Plummer Distribution of Stars Parameters into Standard Units?

In summary, the conversation discusses the goal of distributing N stars with equal mass m within a 3 \times 10^{17} \text{m} box, with total mass M. The document provides equations for calculating the position and velocity of the stars, but there is uncertainty about converting these values to meters and meters per second. The pdf also mentions using uniformly distributed random numbers to calculate these values.
  • #1
jimbo007
41
2
Hi all,
I refer to the following pdf document, in particular the appendix:
http://adsabs.harvard.edu/cgi-bin/n.....37..183A&link_type=ARTICLE&db_key=AST&high=

End goal is to distribute N stars each having mass m (looks like equal mass stars is the easiest scenario) within a box who has each side of length [itex]3 \times 10^{17} \text{m} [/itex] so that the total mass is M. I think I understand that you can't get all stars in the box but as long as most are in the box that should be close enough.

There are some parts of this document I don't understand but will take on faith that it is true.

I do understand how the position (x,y,z) and velocity (u,v,w) are calculated but not sure how to convert them to metres and metres/sec.

Does anyone know how to convert each stars mass m, position (x,y,z) and velocity (u,v,w) into kg, m and m/s?

Thanks!
 
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  • #2
I probably should at least put a few more equations into make things a bit easier. Plummer's density is given by:
[tex]\rho(r) = \frac{3M}{4\pi R^3}\left( 1+ \left(\frac{r}{R} \right)^2 \right)^{-\frac{5}{2}} [/tex]
where
M = total mass of star cluster
R = magic scaling parameter

Now let [itex] X_{n} [/itex] be a uniformly distributed random number between 0 and 1. (x, y, z) is the position of the star and (u, v, w) is the velocity of the star

[tex]
\mathbf{x} = \begin{pmatrix}x \\ y \\ z\end{pmatrix} \\
\dot{\mathbf{x}} = \begin{pmatrix} u \\ v \\ w \end{pmatrix}
[/tex]
then
[tex]
r = \left(X_{1}^{-\frac{2}{3}} - 1 \right)^{-\frac{1}{2}} \\
z = \left( 1-2X_{2} \right) r
[/tex]
x, y, u, v and w and calculated in a similar fashion. The last paragraph in the pdf says to multiply these variables by a few numbers but it's not clear to me how to convert z to metres
 

1. What is the Plummer distribution of stars?

The Plummer distribution is a mathematical model used to describe the distribution of stars in a galaxy or star cluster. It was developed by astronomer William Plummer in 1911 and is based on the assumption that the stars are in equilibrium and have a spherical symmetry.

2. How is the Plummer distribution different from other models?

The Plummer distribution differs from other models, such as the isothermal sphere or King model, because it has a finite radius and density at the center, rather than a singularity. This makes it a more realistic representation of actual star distributions in space.

3. What factors affect the Plummer distribution of stars?

The Plummer distribution is affected by several factors, including the total mass of the system, the radius of the system, and the velocity dispersion of the stars. These parameters can be adjusted to fit observed data and provide insights into the structure and dynamics of the system.

4. Is the Plummer distribution applicable to all types of galaxies?

No, the Plummer distribution is primarily used to model elliptical galaxies and globular clusters, which have a more spherical shape and tend to have older, more concentrated populations of stars. It is not as commonly used for spiral galaxies or irregular galaxies, which have more complex structures and younger star populations.

5. How is the Plummer distribution related to dark matter?

The Plummer distribution is often used in studies of dark matter, as it can help distinguish between the effects of dark matter and the distribution of visible matter in a galaxy. By fitting the observed distribution of stars with a Plummer model, scientists can estimate the amount of dark matter present in a galaxy or cluster.

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