Quote:
Originally Posted by grav
For a particular shape for a galaxy, there is only one mass distribution that will provide for the rotation curve from the center to the rim. That is the point of the iteration, to find it. I have also tried it for different thicknesses for a disk, and the total mass required does not change very much. I'm not accounting for a central supermassive black hole, though, but I could add that in easily enough, but it shouldn't make too much difference either, and spiral arms, which Ken G said shouldn't matter much also, and I hope that's true, since they would probably be very difficult to accommodate for in the program.
|
Nice work grav in working out all these calculations, and so rapidly. I am glad you understand the details of how to do Ken Nicholson's calculations.
I am not sure of the contention that accounting for the spiral arms shouldn't matter much. This is saying that mass variation in the circumferential direction doesn't matter. So take the case of a 2 armed spiral galaxy. If you observe the light variation in the circumferential direction, would you say there is much variation or very little? It looks like a lot of variation to me. If M/L is important in estimating the mass, then I think circumferential variation of light is important, or should at least be checked out to see.
If you are doing a numerical/iterative solution to this problem, can you work in circumferential variation using either a table of mass values, or something like a sine wave mass variation in the circumferential direction. I am really curious about this effect.
Not that you don't have enough to do already :>).
TomT