- Binary Black hole mergers:
- Matter coupled to GR
- Combining characteristic codes
- Critical Phenomena
- Stability issues in the ADM approach
- Perturbations of Robinson Trautman spacetimes with angular momentum

currently incorporating this setup in the AGAVE code developed in this collaboration.

Additionally, a horizon finder is used to track the apparent horizon which we employ to excise the singularity. Initially 2 separate regions are used to excise the singularities present in each hole; however,as time progresses, a single horizon containing both hole is found. At this stage, we employ a single horizon for the excision. Note: care must be taken to define 'good' coordinate conditions. As a first try, we adopted the conditions obtained by the simple addition of the Kerr holes when 2 separate horizons are used and those from a single non-spining hole (of mass 2M) at later times. Naturally, the "single" hole will have angular momentum and we do not expect this condition to be the most appropriate. Yet, as a first test, the result obtained is quite good.

The movie shows the evolution for the metric component g_xx. (This work is part of the Texas-PennState-Pitt collaboration)

Our future plans are:

- Use the initial data solver to provide consisten initial data for the problem.
- Incorporate the horizon trackers in the parallel version of the code .
- Incorporate the matching module to provide boundary data and obtain the waveforms.

- Fissioning of a white hole (MPEG 270K). The movie displays the behavior of an axisymmetric white hole from the early stages (where its geometry approaches that of a sphere) to the time of fissioning into two white holes.
- Fissioning of a white hole (where the a dimension corresponding to the rotation about the axys of revolution has been supressed to include the time axys) (MPEG 200K).
- Head on collision of 2 black holes [global view] (MPEG 140K)
- Closer view of the 2 black hole collision. (MPEG 100K)

of shocks. However with a very crude treatment of the fluid equations we have obtained a remarkable robust code which demonstrates that the characteristic formulation can indeed be of great help in modeling non-vaccum spacetimes. Morover, recent succesful studies by P. Papadopoulos and T. Font on the use of Rieman solvers in a charateristic foliation indicate that with the use of their techniques one can in principle (and rather inexpensively) obtaina robust implementation to study astrophysically relevant scenarios. (This work is done in collaboration with N. Bishop,R. Gomez, M. Maharaj and J. Winicour and the work has been published in PRD).

We here show 3 different movies from our simulations which corresponds to some initial distribution of matter collapsing onto a Schwarzschild black hole.

- Density evolution for the spherical case. Initial data corresponds to a shell of matter (with low pressure). The outer part of the figure corresponds to r=infinity while the inner corresponds to r=2M.
- Density evoltion for the nonspherical case. Initial data corresponds to a blob of matter on the z axis (with low pressure). The left border corresponds to r=infinity while the inner one to r=2M.
- Plus component of the news function for the nonspherical case.

(A manuscript with results can be downloaded in postcript form)