Mass loss in Bonner Ebert simulation?

I wanted to make sure that the bonner ebert sphere would behave as expected under conditions of extreme gravitational instability corresponding to values of the density contrast >> 14.1. Under such conditions, I expected the sphere to collapse to very high densities within a few free fall times. This however, did not happen. What seemed to have happened is concerning. It looks like there is a global mass loss over the grid. Please see the movies in the following link. This sphere has a density contrast ~ 200. I looked again at a sphere that should have been unstable at about rho_o/rho_c ~ 20-30, but was not. This global dip in density also occurred there.

​http://www.pas.rochester.edu/~erica/bonnerWeirdness.html

Also — NO sinks were formed ..

My calculation of mass and mBe:

-volume of ambient = volume of box - volume of sphere

!= 64 - 4/3 Pi

!=60

-mass of ambient = rho_ambient * volume ambient

!= 0.0004 * 60

!= 0.024 (mass - computational units)

-mass of sphere = query result for 'weighted variable sum' of rho (of entire box) - mass of ambient

!= 0.466 (mass - computational units)

To get into cgs, multiply by (rscale/lscale3)?

This gives: 1.57E-73..

I then compared this to mBe:

mBe = [1.18 * (aT)4] / [P½ * G3/2] My simulation gave a 9690 cm/s sound speed (aT) and a pressure of 2.87E-19.

These answers mismatch by an enormous factor, some 50 decades…

Comments

1. Adam Frank -- 13 years ago

It looks like the shere is expanding. Show us the same plots in Log and show us the velocity.

Sounds like you need to go back to basics with the function you are using and the scalings to see what is wrong.

2. Erica Kaminski -- 13 years ago

I remember that there were a series of potential hills and valleys after the critical xi was met. I think depending on which part of the curve you are, there will be different modes of instability present/dominant. This may lead to expansion rather than collapse? Looking at the psuedo color plot of log rho, the sphere is expanding rather uniformly and the numbers suggest that the mass in the sphere is dissipating into the medium, rather than a mass sink which was suggested by the lineout. Vx plot shows the sphere to have some initial inward motion at the core, but that the outward motion dominates throughout. Thanks

3. kris -- 13 years ago

Is there an explanation for why the lineout of phi is not symmetric? I'm guessing it's just that the lineout wasn't stretched across the entire domain?

4. Erica Kaminski -- 13 years ago

Hi Kris, Yes, I did not in this case take special care in getting the line-out to symmetrically span the domain, so I am pretty certain this is the effect you are seeing.

5. kris -- 13 years ago

Ok, cool. Fixing plotting artifacts is a lot easier than fixing code… :)