We consider equatorial motion of particles in the ergoregion of generic axially symmetric rotating black holes. We introduce the notion of zero energy observers (ZEOs) as counterparts to known zero angular observers (ZAMOs). It is shown that the trajectory of a ZEO has precisely one turning point that lies on the boundary of the ergoregion for photons and inside the ergoregion for massive particles. As a consequence, such trajectories enter the ergosphere from the white hole region under horizon and leave it crossing the horizon again (entering the black hole region). The angular velocity of ZEO does not depend on the angular momentum. For particles with $% E>0$ this velocity is bigger than for a ZEO, for $E<0$ it is smaller. General limitations on the angular momentum are found depending on whether the trajectory lies entirely inside the ergoregion, bounces back from the boundary or intersects it. These results generalize the recent observations made in A. A. Grib, Yu. V. Pavlov, arXiv:1601.02592 for the Kerr metric. We also show that collision between a ZEO and a particle with $E\neq 0$ near a black hole can lead to the unbound energy in the centre of mass thus giving a special version of the Bañados - Silk - West effect.
On geodesics with negative energies in the ergoregions of dirty black holes
我们考虑在一般旋转的“脏”（被物质包围）黑洞的能区中具有负能量的赤道测地线的行为。结果表明，在非常简单和一般的条件下的度量系数，没有这样的圆轨道。这意味着这种测地线必须在事件视界下产生和终止。这些结果推广了A. A. Grib，Yu.巴甫洛夫（V.Pavlov）和V. Vertogradov，Mod. Phys. Lett. 29，1450110（2014）[arXiv：1304.7360].
Constrained thermodynamics and geodesic observables of an effective non-commutative Kerr-like black hole
California State University, Fresno（弗雷斯诺州立大学）；University of Hradec Králové（赫拉德茨克拉洛韦大学）；Khazar University（哈扎尔大学）；UAEH（墨西哥自治高等教育学院）；Cinvestav（墨西哥国立科学研究与高级研究中心）；Universidad de Valladolid（巴利亚多利德大学）；University of Helsinki（赫尔辛基大学）
Energy extraction and particle acceleration around a rotating dyonic black hole in $N=2$, $U(1)^2$ gauged supergravity
H. N. B. Garhwal University（H.N.B. 加尔瓦尔大学）；Gurukul Kangri Vishwavidyalaya（古鲁库尔坎格里大学）；Center for Space Research, North-West University（西北大学空间研究中心）；Instituto de Física, Pontificia Universidad Católica de Valparaíso（天主教瓦尔帕莱索大学物理研究所）；University of York（约克大学）
