Magnetized accretion disks around Kerr black holes with scalar hair: Constant angular momentum disks

Abstract

Testing the true nature of black holes -the no-hair hypothesis -will become increasingly more precise in the next few years as new observational data is collected in both the gravitational wave channel and the electromagnetic channel. In this paper we consider numerically generated spacetimes of Kerr black holes with synchronised scalar hair and build stationary models of magnetized thick disks (or tori) around them. Our approach assumes that the disks are not self-gravitating, they obey a polytropic equation of state, the distribution of their specific angular momentum is constant, and they are marginally stable, i.e. the disks completely fill their Roche lobe. Moreover, contrary to existing approaches in the literature, our models are thermodinamically relativist, as the specific enthalpy of the fluid can adopt values significantly larger than unity. We study the dependence of the morphology and properties of the accretion tori on the type of black hole considered, from purely Kerr black holes with varying degrees of spin parameter, namely from a Schwarzschild black hole to a nearly extremal Kerr case, to Kerr black holes with scalar hair with different ADM mass and horizon angular velocity. Comparisons between the disk properties for both types of black holes are presented. The sequences of magnetized, equilibrium disks models discussed in this study can be used as initial data for numerical relativity codes to investigate their dynamical (non-linear) stability and used in tandem with ray-tracing codes to obtain synthetic images of black holes (i.e. shadows) in astrophysically relevant situations where the light source is provided by an emitting accretion disk.PACS numbers: 95.30. Sf, 04.70.Bw, 04.25.dg 95.30.Qd

Non-linear evolutions of magnetized thick discs around black holes: dependence on the initial data

“…Finally, we note that the similarities we have found in the evolutions of approaches KMh and KMρ are expected due to the small deviation of the value h 1 for a potential gap of |∆W | = 0.2216. However, other types of compact objects might provide larger potential gaps (e.g., the Kerr black holes with scalar hair described in Gimeno-Soler et al (2019) achieve values of |∆W | > 1). For this reason, we could expect to find differences in the evolution between approaches KMh and KMρ for such central objects even for low magnetised discs.…”

“…(26) that ρ c = 1/(1 − |W c − W in |) < 1. The interested reader is addressed to Gimeno-Soler & Font (2017) and Gimeno-Soler et al (2019) for an extensive discussion on the morphology of magnetised discs for different degrees of magnetisation.…”

“…To this aim we build magnetised Polish doughnuts around rotating black holes, neglecting the self-gravity of the discs and using three different approaches to account for the magnetic field, namely: i) a purely hydrodynamical solution (see e.g. Abramowicz et al (1978); Font & Daigne (2002); Daigne & Font (2004)) in which an 'ad hoc' toroidal magnetic field is seeded afterwards; ii) the self-consistent solution from Komissarov (2006), in which the distribution of the rest-mass density of the disc is coupled to the toroidal magnetic field through the equation of state for the magnetic pressure; this approach assumes that the fluid is thermodynamically non-relativistic; and iii) the self-consistent approach of Komissarov (2006) but dropping the assumption of a thermodynamically nonrelativistic fluid, as done in Montero et al (2007) and Gimeno-Soler et al (2019). Using these three approaches we build initial data and compare their non-linear dynamical evolutions by means of axisymmetric numerical simulations, finding interesting differences.…”

Kerr black holes with synchronised scalar hair and higher azimuthal harmonic index

“…The results herein indicate no significant differences are to be expected with respect to the m = 1 case in these models. It would, nonetheless, be interesting to study some phenomenological properties of this higher m solutions, such as BH shadows [17,28], X-ray spectrum [31], accretion disk morphology [64] or star trajectories [38], since these higher m solutions could play a role in the dynamical evolution of the BH/fundamental field system, in case such fundamental, ultra-light, scalar or vector fields exist in Nature.…”

Distinguishing gravitational and emission physics in black-hole imaging: spherical symmetry

“…Thus, proposing and developing semi-analytical accretion and emission models (Bambi & Modesto 2013;Younsi et al 2016;Pu & Broderick 2018;Gimeno-Soler et al 2019;Narayan et al 2019;Gan et al 2021;Yang et al 2021), and studying the variation of image features with these models and with varying spacetime geometry, as a path-finding step, could already yield important insights. Such analyses require fewer expensive operations such as integrations, and greatly reduce the overall computational cost, enabling a broader parameter survey.…”