How Reissner-Nordström black holes behave part1(Astrophysics)
- Efficiency of Penrose process in spacetime of axially symmetric magnetized Reissner-Nordström black hole(arXiv)
Author : Sanjar Shaymatov, Pankaj Sheoran, Ricardo Becerril, Ulises Nucamendi, Bobomurat Ahmedov
Abstract : In this paper, we investigate the Penrose process in the purlieus of the axially symmetric magnetized Reissner-Nordström black hole for both neutral and charged particles. We start with the study of the geometry of the black hole and find the regions where the gtt component of the metric tensor is positive (i.e., gtt>0). It is interestingly found that the condition gtt>0 is fulfilled not only close to the event horizon known as the ergosphere but also far away from the event horizon in the silhouette of potential wells. We also show that as the dimensionless magnetic field B increases the silhouette of potential wells for which gtt>0 grows correspondingly and eventually merges with the ergoregion when B≳1.6. Finally, we investigate the efficiency of the Penrose process for the axially symmetric magnetized black hole case and bring out the effect of the magnetic field on it. Further, we also compare our results with the one for Kerr black hole. We show that when the charge Q of the black hole is kept constant, the efficiency of the energy extraction process for the case of {a neutral particle (i.e., q/m=0) first increases and then begins to decrease with rise in the value of B field, in contrast to Kerr black hole where it always increases as the rotation parameter grows. However, for the case of a charged particle (i.e., q≠0) the efficiency always increases with the rise in the B field and can go over 100%, when both B and q/m are large enough (say B≈1 and q/m>2.2)}. It is worth noting that the existence of regions away from the horizon where gtt>0 also favors the energy-extraction process away from the effect of the black hole. However, the energy extraction from these regions is pure consequence of the magnetic field.
2. Quasinormal modes for massive charged scalar fields in Reissner-Nordström dS black holes: anomalous decay rate(arXiv)
Author : P. A. González, Eleftherios Papantonopoulos, Joel Saavedra, Yerko Vásquez
Abstract : The anomalous decay rate of the quasinormal modes occurs when the longest-lived modes are the ones with higher angular number. Such behaviour has been recently studied in different static spacetimes, for uncharged scalar and fermionic perturbations, being observed in both cases. In this work we consider the propagation of charged massive scalar fields in the background of Reissner-Nordström-de Sitter black holes and we mainly study the effect of the scalar field charge in the spectrum of quasinormal frequencies, as well as, its effect on the anomalous decay rate. Mainly, we show that the anomalous behaviour is present for massive charged scalar fields as well, and a critical value of scalar field mass exists, beyond which the behaviour is inverted. However, there is also a critical value of the parameter qQ of the charge of the scalar field and of the charge of the black hole, which increases when the cosmological constant increases, and beyond the critical value the anomalous behaviour of the decay rate could be avoided for the fundamental mode.
3.Entropy of Reissner-Nordström-like black holes (arXiv)
Author : Milutin Blagojević, Branislav Cvetković
Abstract : In Poincaré gauge theory, black hole entropy is defined canonically by the variation of a boundary term ΓH, located at horizon. For a class of static and spherically symmetric black holes in vacuum, the explicit formula reads δΓH=TδS, where T is black hole temperature and S entropy. Here, we analyze a new member of the same class, the Reissner-Nordström-like black hole with torsion [1], where the electric charge of matter is replaced by a gravitational parameter, induced by the existence of torsion. This parameter affects δΓH in a way that ensures the validity of the first law.
