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[Zach Etienne]

One quick clarification:

When I said
> "[integrated measures of rest mass over a volume] can become completely
unreliable at the time of black hole formation"

I meant that the conservative nature of GRMHD schemes can and do break down
inside black holes, so mass might be lost after it passes inside a black
hole horizon. This should have no ill effect outside the horizon, as "what
happens in the horizon stays in the horizon". Generally you'd want to
perform a surface integral to monitor the rest mass passing into the
horizon and combine it with a volume integral outside the horizon to
measure the total rest mass after black hole formation.

-Zach

*     *     *
Prof. Zachariah Etienne
Physics & Astronomy Dept.
West Virginia University
http://astro.phys.wvu.edu/zetienne/
http://blackholesathome.net
<https://blackholesathome.net>


On Wed, Feb 12, 2020 at 11:05 PM Zach Etienne <zachetie at gmail.com> wrote:

> Hi ZhiChao,
>
> > The program runs without error, however there is no eject during the
> merge.
>
> Typical ejecta from BNS mergers amount to a very tiny fraction of the
> total initial mass, with values of 1e-3 Msun from BNS merger simulations
> being reported in the literature (https://arxiv.org/abs/1809.11161). This
> value is highly dependent on the equation of state however. Further most
> simulations reporting ejecta are not performed at multiple numerical
> resolutions, meaning that the values may be adjusted downwards with
> subsequent simulations. Indeed in most simulations I saw for which more
> than one resolution was performed in that paper, the higher resolution
> simulation has less ejecta (see Table 2)--sometimes significantly less
> (e.g., LS220_M140140_LK).
>
> Bottom line, I am not surprised you didn't see any ejecta. Ejecta
> measurements are often dominated by numerical error, and depend sensitively
> on equation of state. The very simple equation of state you chose (simple
> Gamma=2 polytrope) might not exhibit much, if any, ejecta in the limit of
> very high resolution.
>
> A recent update to IllinoisGRMHD supports more sophisticated (piecewise
> polytrope/"hybrid") equations of state. It exists within the IllinoisGRMHD
> subdirectory of https://github.com/zachetienne/nrpytutorial . You might
> have more luck getting ejecta from BNS initial data with
> piecewise-polytrope equations of state.
>
> > And "restmass. Init. IN sphere @
> (0.000000e+00,0.000000e+00,0.000000e+00), r=2.708902e+02. Moves/Tracks AMR
> Centre -1/-1" is increasing.
>
> If I'm interpreting this correctly (I might not be), you are measuring
> total rest mass within 270.89 in code units. You seem to observe an
> increase of 0.06% over the course of the simulation. That's not much, and
> can happen due to interpolation errors at AMR refinement boundaries (matter
> crosses AMR refinement boundaries and tiny errors add up to a small boost
> in mass), or become completely unreliable at the time of black hole
> formation. Performing another simulation at higher or lower resolution and
> additional volume integral regions may help diagnose this measurement. I
> think you'd want to analyze the rest mass *outside* an interior volume to
> estimate ejecta anyway.
>
> A more sophisticated interpolation treatment at AMR refinement boundaries
> might help reduce this error, which amounts to a different prolongation
> type (e.g., ENO) being chosen for evolved GRMHD variables.
>
> Hope this helps.
>
> -Zach
>
> *     *     *
> Prof. Zachariah Etienne
> Physics & Astronomy Dept.
> West Virginia University
> http://astro.phys.wvu.edu/zetienne/
> http://blackholesathome.net
> <https://blackholesathome.net>
>
>
> On Wed, Feb 12, 2020 at 9:25 PM ZhiChao Zhao <yanyuechuixue at gmail.com>
> wrote:
>
>> Hello everyone,
>>
>> I am Zhi-Chao Zhao from Beijing Normal University, China.
>> I am using EinsteinToolkit and IllinoisGRMHD to simulate BNS merge.
>>
>> I use a par file modified from
>> https://bitbucket.org/zach_etienne/wvuthorns_diagnostics/src/master/NSNS_parameter_files/nsns_test.par
>>  .
>> I just add one line
>> "VolumeIntegrals_GRMHD::volintegral_inside_sphere__radius[6] =
>> 270.89015422746235".
>>
>> The initial data is got from Zach Etienne.
>>
>> The program runs without error, however there is no eject during the
>> merge.
>> Two videos:
>> https://gogo.treenew.be/rho_b_movie.mpg
>> https://gogo.treenew.be/rho_b_log_movie.mpg
>>
>>
>> And "restmass. Init. IN sphere @
>> (0.000000e+00,0.000000e+00,0.000000e+00), r=2.708902e+02. Moves/Tracks AMR
>> Centre -1/-1" is increasing.
>> One figure:
>> https://gogo.treenew.be/newplot.png
>>
>> I don't know where I went wrong. Can anyone help me?
>>
>>
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>>
>
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