RhoAlpha

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$/AEI1998\$ $/AEI2001\$ $/NCSA1995\$ $/NCSA1999\$ $/Others\$
$/BlackHoles\$ $/BrillWaves\$ $/NeutronStars\$
$/Headon\$ $/Meudon_129_IVP\$ $/Meudon_161_IVP\$ $/Newton\$
$/RhoAlpha\$ $/RhoBeta\$

Evolution of the lapse function from Colliding Neutron Stars

Shown is the lapse function (\alpha) as a colored height field beyond density isosurfaces (rho=10^-5 in geometric units at the outermost level, i.e. ~1/10 rho_central ). The time unit T is given in solar mass units.

Generally, the lapse is an indication for the strongness of the gravitational field. Small values of the lapse mean strong gravity (high space curvature), and within black holes the lapse may approach the zero value, meaning that numerical evolution comes to a stillstand there. This is a desired effect to avoid numerical evolution schemes running into physical singularities, but it leads to severe grid-stretching problems under certain circumstances. A lapse of 1.0 is the same as usual in flat Minkowski spacetime.

The centers of the two initial neutron stars already contain a huge gravitational field, which is reflected visually by the two initial funnels below the neutron stars' centers. During evolution, these two funnels, corotating with the neutron stars, approach and finally merge to a single, but deeper funnel.

Possibly a black hole was created at this moment, but we don't know this from these simulation data.

Simulation code:

AEI , WashU
Meudon Initial Data: Silvano Bonazzola, Eric Gourgoulhon and Jean-Alain Marck
(see gr-qc/9810072 and gr-qc/9904040)

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