Current research topics include:


Collision of Boosted black holes:

Initial data is set up by simply adding 2 kerr black holes (with mass M=1,a=0.5) which are boosted towards each other in a "grazing" set up (with |v|=0.5).The evolution is carried out with the evolution code developed by the BBHGCA and we are
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:

Although there is still much more to do, present results are quite encouraging.
 
 

Fissioning of a white hole <-> Collision of 2 black holes

Using the characteristic formulation, it is possible to construct a model for a fissioning white hole horizon. In a reversepoint of view, this corresponds to the head-on collision of 2 black holes. (This work is done in collaboration with N. Bishop, R. Gomez, J. Winicour and B. Szilagyi and a manuscript can be consulted for details)

Matter in the characteristic formulation of G.R.

By modifying the vaccum characteristic code to incorporate fluids, we have studied the feasibility of using a characteristic evolution to model spacetimes with matter. At this point our matter treatment can not handle the presence

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.

Combining characteristic codes

This approach involves combining and ingoing and an outgoing characteristic code so that both the inner region and null infinity can be accessed. The main goal is to be able to employ the characteristic formulation to simulate a Neutron Start collapsing on to a black hole. Having the incoming formulation model the spacetime in the vicinity of the black hole enables us to study phisiscally interesting phenomena like mass accretion. On the other hand, an outgoing formulation is used to model the equations far from the black hole all the way to future null infinity; thus being able to obtain physical quantities without ambiguities. As a first test of this approach I studied the Einsteing-Klein-Gordon system obtaining excellent results which indicate the combination of these formulation might be a valuable tool for astrophysically relevant simulations.
(A manuscript with results can be downloaded in postcript form)