Super-spinning compact objects and models of high-frequency quasi-periodic oscillations observed in Galactic microquasars

Abstract

In our previous work (Paper I) we applied several models of high-frequency quasi-periodic oscillations (HF QPOs) to estimate the spin of the central compact object in three Galactic microquasars assuming the possibility that the central compact body is a superspinning object (or a naked singularity) with external spacetime described by Kerr geometry with a dimensionless spin parameter a ≡ cJ/GM 2 > 1. Here we extend our consideration, and in a consistent way investigate implications of a set of ten resonance models so far discussed only in the context of a < 1. The same physical arguments as in Paper I are applied to these models, i.e. only a small deviation of the spin estimate from a = 1, a 1, is assumed for a favoured model. For five of these models that involve Keplerian and radial epicyclic oscillations we find the existence of a unique specific QPO excitation radius. Consequently, there is a simple behaviour of dimensionless frequency M × ν U (a) represented by a single continuous function having solely one maximum close to a 1. Only one of these models is compatible with the expectation of a 1. The other five models that involve the radial and vertical epicyclic oscillations imply the existence of multiple resonant radii. This signifies a more complicated behaviour of M × ν U (a) that cannot be represented by single functions. Each of these five models is compatible with the expectation of a 1.

Spherical photon orbits in the field of Kerr naked singularities

“…Here and in the following, we restrict our discussion on the 'northern' hemisphere (0 ≤ θ ≤ π/2), the situation in the 'southern' hemisphere is symmetric with respect to the equatorial plane. Second family of the SPOs spreads between the inner co-rotating (red dot) and outer counter-rotating (blue dot) equatorial circular orbits with radii given by (27). There is no turning point of the azimuthal motion for orbits with radii r ph+ < r < r pol− , where r pol− is the radius of the polar spherical orbit (purple ellipse) given by (37), and all such photons are prograde.…”

“…Recently, growing interest in Kerr naked singularity spacetimes is demonstrated, mainly due to the possibility of existence of Kerr superspinars proposed in the framework of String theory by Hořava and his co-workers, with interior governed by the String theory and exterior described by the Kerr naked singularity geometry [25,50,52]. The presence of Kerr superspinars in active galactic nuclei or in microquasars could give clear signatures in the ultra-relativistic collisional processes [53], in the high-frequency quasiperiodic oscillations in Keplerian disks [27,28,59], or in the Lense-Thirring precession effects [16]. The instability of test fields in the Kerr naked singularity backgrounds has been studied in [14,21], possible stabilizing effects were demonstrated for the Kerr superspinars in [33].…”

Supermassive black holes surrounded by dark matter modeled as anisotropic fluid: epicyclic oscillations and their fitting to observed QPOs

“…However, we cannot exclude some alternative objects to black holes as the source of strong gravity in the microquasars and active galactic nuclei that could lie behind the observed HF QPOs. As such alternatives can be considered the Kerr naked singularities and superspinars [43][44][45][46][47], or wormholes [48]. Here we continue the study of the possible role of the dark matter concentrated around accreting black holes on the character of the HF QPOs generated in the Keplerian disks and fit the theoretical predictions to the observational data.…”

Mass of the active galactic nucleus black hole XMMUJ134736.6+173403

“…The mass-spin relations predicted for Galactic microquasars by several QPO models have been investigated in a series of works (Török et al 2011;Kotrlová et al 2014Kotrlová et al , 2017. Along with the TD, RP, ER, and KeP model, these include the specific diskoseismic model of Kato (2001Kato ( , 2007Kato ( , 2008 and two models introduced by Bursa (2005) and Török et al (2007Török et al ( , 2010 that were motivated by the observations of NS QPOs (the RP1 and RP2 models).…”