Using the generalized uncertainty principle, we calculate the entropy of the charged dilaton-axion black hole for both asymptotically flat and non-flat cases by counting degrees of freedom near the horizon. The divergence of density of states and free energy appearing in the thin film brick-wall model is removed without any cutoff. The entropy proportional to the horizon area is derived from the contribution of the vicinity of the horizon.
This work investigates the feasibility of detecting close, detached, black hole-red dwarf binaries, which are expected to be evolutionary precursors of low-mass X-ray binaries (LMXBs). Although this pre-low-mass X-ray binary (pre-LMXB) phase of evolution is predicted theoretically, as yet no such systems have been identified observationally. The calculations presented here suggest that the X-ray luminosity of black hole wind accretion in a pre-LMXB system could exceed the intrinsic X-ray luminosity of the red dwarf secondary star, thereby providing a detection mechanism. However, there is significant uncertainty regarding the efficiency of the conversion of gravitational potential energy to X-ray luminosity resulting from accretion onto a black hole, for example energy may be lost via advection across the event horizon. Still, sources with X-ray luminosities greater than that expected for a red dwarf star, but whose positions coincide with that of a red dwarf would represent candidate pre-LMXB systems. These candidates should be surveyed for the radial velocity shifts that would occur as a result of the orbital motion of a red dwarf star within a close binary system containing a black hole.
In a series of papers it was discussed,on the basis of phenomenological arguments, whether the high frequency quasiperiodic oscillations (kHz QPOs)observed in the neutron-star and black-hole X-ray sources originate in the same physical mechanism. Recently it was suggested that a general trend seen in neutron star kHz QPOs instead excludes such a uniform origin. Using the example of the atoll source 4U 1636-53 we illustrate that this is not neccesarily true.
We present the quasinormal frequencies of the massive scalar field in the background of a Schwarzchild black hole surrounded by quintessence with the third-order WKB method. The mass of the scalar field u plays an important role in studying the quasinormal frequencies, the real part of the frequencies increases linearly as mass of the field u increases, while the imaginary part in absolute value decreases linearly which leads to damping more slowly than the massless scalar field. The frequencies have a limited value, so it is easier to detect the quasinormal modes. Moreover, owing to the presence of the quintessence, the massive scalar field damps more slowly.
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