[Users] Determination of the final spin of the remnant of a binary neutron star merger

Roland Haas rhaas at illinois.edu
Thu Mar 5 10:33:50 CST 2020

Hello all,

for a (somewhat recent, likely not the first nor the latest) study of
how well this particular way of measuring spin of a neutron star works,
you may want to consult sections III.C (in particular figure 9) of
https://arxiv.org/abs/1508.06986 which deals with both initial data
construction and evolution (though not in the context of the Einstein
Toolkit). The method used is the one Erik suggested.


> Beyhan
> The QuasiLocalMeasures thorn can examine not only horizons, but also
> other 2-surfaces. You can set up a surface that is large and which
> encloses both the remnant and surrounding matter, but which is still
> inside the emitted gravitational wave train. QuasiLocalMeasures can
> then calculate the angular momentum contained inside that sphere.
> As Zach mentioned, the details of setting up a parameter file to do so
> are difficult to explain over email. The example parameter file
> "Cactus/par/qc0-mclachlan.par" contains such a setup; surface #3
> ("horizon" #4, although this surface is of course not a horizon) is a
> sphere with areal radius R=50 where such quantities are calculated.
> -erik
> On Wed, Mar 4, 2020 at 11:22 AM Beyhan Karakaş <beyhannkarakas at gmail.com> wrote:
> >
> > Dear to whom it may concern,
> >
> >   I am interested in determining the spin of the remnant which are resulted from binary neutron star (initially are in irrotational configuration) merger . How could the method to determine the final spin differ (if it does) in case of remnant is a black hole or a neutron star. For the former case, I suppose QuasiLocalMeasures parameter "begin_qlm_calculations_after"  along with AHFinderDirect parameter "find_after_individual" should be set to the time/iteration that the black hole formed. If this is not the case, please clarify how could it be determined? In addition, is there a way to find the evolution of the spin and orbital eccentricity of the binary?
> >
> > Best regards,
> >
> > Beyhan.
> > _______________________________________________
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> > Users at einsteintoolkit.org
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