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Register a new userOscillation modes of relativistic slender tori
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Accretion flows with pressure gradients permit the existence of standing waves which may be responsible for observed quasi-periodic oscillations (QPOs) in X-ray binaries. We present a comprehensive treatment of the linear modes of a hydrodynamic, non-self-gravitating, polytropic slender torus, with arbitrary specific angular momentum distribution, orbiting in an arbitrary axisymmetric spacetime with reflection symmetry. We discuss the physical nature of the modes, present general analytic expressions and illustrations for those which are low order, and show that they can be excited in numerical simulations of relativistic tori. The mode oscillation spectrum simplifies dramatically for near Keplerian angular momentum distributions, which appear to be generic in global simulations of the magnetorotational instability. We discuss our results in light of observations of high frequency QPOs, and point out the existence of a new pair of modes which can be in an approximate 3:2 ratio for arbitrary black hole spins and angular momentum distributions, provided the torus is radiation pressure dominated. This mode pair consists of the axisymmetric vertical epicyclic mode and the lowest order axisymmetric breathing mode.
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We simulate an oscillating purely hydrodynamical torus with constant specific angular mo- mentum around a Schwarzschild black hole. The goal is to search for quasi-periodic oscil- lations (QPOs) in the light curve of the torus. The initial torus setup is subjected to radial, vertical and diagonal (combination of radial and vertical) velocity perturbations. The hydro- dynamical simulations are performed using the general relativistic magnetohydrodynamics code Cosmos++ and ray-traced using the GYOTO code. We found that a horizontal velocity perturbation triggers the radial and plus modes, while a vertical velocity perturbation trig- gers the vertical and X modes. The diagonal perturbation gives a combination of the modes triggered in the radial and vertical perturbations.
Context. Some microquasars exhibit millisecond quasi-periodic oscillations (QPO) that are likely related to phenomena occuring in the immediate vicinity of the central black hole. Oscillations of accretion tori have been proposed to model these QPOs. Aims. Here, we aim at determining the observable spectral signature of slender accretion tori surrounding Kerr black holes. We analyze the impact of the inclination and spin parameters on the power spectra. Methods. Ray-traced power spectra of slender tori oscillation modes are computed in the Kerr metric. Results. We show that the power spectral densities of oscillating tori are very sensitive to the inclination and spin parameters. This strong dependency of the temporal spectra on inclination and spin may lead to observable constraints of these parameters. Conclusions. This work goes a step further in the analysis of the oscillating torus QPO model. It is part of a long-term study that will ultimately lead to comparison with observed data.
We present a comprehensive numerical study of the dynamics of relativistic axisymmetric accretion tori with a power-law distribution of specific angular momentum orbiting in the background spacetime of a Kerr black hole. By combining general relativistic hydrodynamics simulations with a linear perturbative approach we investigate the main dynamical properties of these objects over a large parameter space. The astrophysical implications of our results extend and improve two interesting results that have been recently reported in the literature. Firstly, the induced quasi-periodic variation of the mass quadrupole moment makes relativistic tori of nuclear matter densities, as those formed during the last stages of binary neutron star mergers, promising sources of gravitational radiation, potentially detectable by interferometric instruments. Secondly, $p$-mode oscillations in relativistic tori of low rest-mass densities could be used to explain high frequency quasi-periodic oscillations observed in X-ray binaries containing a black hole candidate under conditions more generic than those considered so far.
We perform a detailed analysis of the fundamental $f$-mode frequencies and damping times of nonrotating boson stars in general relativity by solving the nonradial perturbation equations. Two parameters which govern the microscopic properties of the bosonic condensates, namely the self-coupling strength and the mass of scalar particle, are explored. These two quantities characterize oscillations of boson star. Specifically, we reexamine some empirical relations that describe the $f$-mode parameters in terms of mass and radius of the boson stars. We found it is possible to constrain the equation of state if the fundamental oscillation mode is observed.
We show that gapless modes in relativistic hydrodynamics could become topologically nontrivial by weakly breaking the conservation of energy momentum tensor in a specific way. This system has topological semimetal-like crossing nodes in the spectrum of hydrodynamic modes that require the protection of a special combination of translational and boost symmetries in two spatial directions. We confirm the nontrivial topology from the existence of an undetermined Berry phase. These energy momentum non-conservation terms could naturally be produced by an external gravitational field that comes from a reference frame change from the original inertial frame, i.e. by fictitious forces in a non-inertial reference frame. This non-inertial frame is the rest frame of an accelerating observer moving along a trajectory of a helix. This suggests that topologically trivial modes could become nontrivial by being observed in a special non-inertial reference frame, and this fact could be verified in laboratories, in principle. Finally, we propose a holographic realization of this system.
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