[Users] LORENE BHNS Initial Data

[Roland Haas]

Hello Gwyneth, Frank, all,

> Thanks for all the comments! I'm looking forward to trying this out.
> 
> Once I manage to compile Lorene and produce some data, I'll have a go at
> importing the data into the toolkit. There's probably going to be a
> learning curve, but I don't mind spending some time on this. If I manage to
> get it working, I'll add to the wiki.
I was pointed out to me by a kind person that there is indeed a simpler
way to get at "some" bhns initial data. You can use a combination of
the TOVSolver and TwoPunctures thorns to obtain such a one as shown in
the test parfile
arrangements/EinsteinInitialData/TwoPunctures/test/bhns_eval.par 

You will probably have to run with quite high values for npoints_A and
npoints_B (easily >60) to obtain any reasonable value for the
constraints.

This will not generate great (or even good) initial data since at the
very least the star will be out of hydrostatic equilibrium so will
start to oscillate noticeably when the simulation stars. Second the
example parfile has the star at rest. You can give it a velocity via
TOVSolver's TOV_Velocity_x[0] etc parameters though then you will not
even strictly satisfy the initial data constraints for the metric since
TOVSolver does not take the fluid into account when solving for the
momentum constraint. Finally there is no help provided to obtain
quasicircular orbits at all, so you are stuck with eg starting from the
Newtonian velocity and see what happens.

As said, not great initial data for BHNS but something that you could
at least play with while learning how to use LORENE or getting access
to better data produced by other codes.

Yours,
Roland

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