31. Piotr T. Chru¶ciel, Michał Eckstein, Sebastian J. Szybka On smoothness of Black Saturns Journal of High Energy Physics, vol. 2010, pp. 139 (2010). [abstract] [preprint] [journal] 
Abstract: We prove smoothness of the domain of outer communications (d.o.c.) of the Black Saturn solutions of Elvang and Figueras. We show that the metric on the d.o.c. extends smoothly across two disjoint event horizons with topology R x S^3 and R x S^1 x S^2. We establish stable causality of the d.o.c. when the Komar angular momentum of the spherical component of the horizon vanishes, and present numerical evidence for stable causality in general. 
32. Sikora S. On derivation of metric from light deflection angle in the static, spherically symmetric spacetime Acta Phys. Pol., B , vol. 41, pp. 219221 (2010). [abstract] [journal] [download] 
Abstract: In this note general relativistic light deﬂection in the static, spherically symmetric spacetime is investigated as a means to determine the metric of the spacetime. It is shown that in this case derivation of spacetime metric is ambiguous from the light deﬂection angle only.

33. Sebastian J. Szybka Chaos and Vacuum Gravitational Collapse Proceedings of the Spanish Relativity Meeting 2008, AIP Conf. Proc., vol. 1122, pp. 172178 (2009). [abstract] [journal] 
Abstract: The numerical evidence for chaotic behavior in vacuum gravitational collapse is presented. The collapse is studied in five dimensional vacuum spacetimes satisfying the cohomogeneitytwo triaxial Bianchi typeIX ansatz. 
34. Leszek M. Sokołowski Stability of a metric f(R) gravity theory implies the Newtonian limit Acta Phys. Polon., vol. B39, pp. 28792901 (2008). [abstract] [preprint] [journal] 
Abstract: We show that the existence of the Newtonian limit cannot work as a selection rule for choosing the correct gravity theory fromm the set of all L=f(R) ones. To this end we prove that stability of the ground state solution in arbitrary purely metric f(R) gravity implies the existence of the Newtonian limit of the theory. And the stability is assumed to be the fundamental viability criterion of any gravity theory. The Newtonian limit is either strict in the mathematical sense if the ground state is flat spacetime or approximate and valid on length scales smaller than the cosmological one if the ground state is de Sitter or AdS space. Hence regarding the Newtonian limit a metric f(R) gravity does not differ from GR with arbitrary Lambda. This is exceptional to Lagrangians solely depending on R and/or Ricci tensor. An independent selection rule is necessary. 
35. Piotr T. Chru¶ciel, Sebastian J. Szybka On the Ernst electrovacuum equations and ergosurfaces Acta Phys. Pol., B , vol. 39, pp. 5975 (2008). [abstract] [preprint] [journal] 
Abstract: The question of smoothness at the ergosurface of the spacetime
metric constructed out of solutions (E,phi) of the Ernst electrovacuum equations is considered. We prove smoothness of those ergosurfaces at which Re(E) provides the dominant contribution to f=(Re(E)+phi^2) at the zerolevelset of f. Some partial results are obtained in the remaining cases: in particular we give examples of leadingorder solutions with singular isolated ``ergocircles". 
36. Sebastian J. Szybka, Tadeusz Chmaj Fractal Threshold Behavior in Vacuum Gravitational Collapse Phys. Rev. Lett., vol. 100, p. 101102 (2008). [abstract] [preprint] [journal] [download] 
Abstract: We present the numerical evidence for fractal threshold behavior in the five dimensional vacuum Einstein equations satisfying the cohomogeneitytwo triaxial Bianchi typeIX ansatz. In other words, we show that a flip of the wings of a butterfly may influence the process of the black hole formation. 