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Oscillation models of accretion disks

Present level of knowledge and research activity

(at the beginning of the project)

Several Galactic black hole sources in low X-ray mass binaries show both chaotic and quasi periodic variability in their observed X-ray fluxes. Some of the quasi periodic oscillations (QPOs) are in the kHz range and often come in pairs of twin peaks in the Fourier power spectra [1, 2].

There is no general agreement on a physical mechanism exciting twin peak QPOs. Kluzniak and Abramowicz suggested in 2000 [3,4] that QPOs are due to a resonance between accretion disk oscillation modes. The resonance model is based on fundamental features of strong gravity. The model predicts twin peak kHz QPOs frequencies with values and ratios corresponding to those observed. However, at the moment, it is rather vague in explaining how then X-ray flux is actually modulated by the resonant disk oscillations.

[1] M. van der Klis, Ann. Rev. of A&A, 38, 717 2000
[2] J. E. McClintock and R. A. Remillard astro-ph/0306213, 2003
[3] M. A. Abramowicz and W. Kluzniak, Astronomy and Astrophysics, 374, L19, 2001.
[4] W. Kluzniak and M. A. Abramowicz, Acta Physica Polonica B, B32, 3605, 2001.
[5] Gabriel Török, Marek Abramowicz, Wlodek Kluzniak, Zdeněk Stuchlík, Astronomy and Astrophysics, The orbital resonance model for twin peak kHz quasi periodic oscillations (odesláno do tisku)
[6] Gabriel Török, Astronomy and Astrophysics, A possible 3:2 orbital epicyclic resonance in QPOs frequencies of Sgr A* (odesláno do tisku)
[7] Gabriel Török a Zdeněk Stuchlík, Astronomy and Astrophysics, Radial and vertical epicyclic frequencies of Keplerian motion in the field of Kerr naked singularities (odesláno do tisku)
[8] M.A. Abramowicz, W. Kluzniak, J. Mc Clintock, R. Remillard, The Importance of Discovering a 3:2 Twin-Peak Quasi-periodic Oscillation in an Ultraluminous X-Ray Source, or How to Solve the Puzzle of Intermediate-Mass Black Holes, 2004, ApJ, 609L, 63A

Basic ideas of our research plan in the proposed area

We propose to study short time variability and oscillations in accretion disks around black holes and neutron stars. These studies are of fundamental importance for astrophysics and theoretical physics. Black holes belong to the most remarkable inventions of the human mind. Their studies are important for modern theoretical physics because they test our knowledge of fundamental properties of space and time and cast light on quantum gravity structure of physical vacuum. Accretion disks provide energy for radiation in astronomical sources that contain black holes, and we could only "observe" black holes indirectly: by observing their accretion disks. Thanks to precise timing of double pulsar's orbital decay, the weak field limit of Einstein's theory is far better tested than any other physical theory. However, the most interesting and bizarre predictions of Einstein's theory deal not with the weak field, but with the extremely strong field regime and these have never been tested. Thus, the very question: “Was Einstein right?” remains unanswered. One may argue that in a foreseeable future there will be no way to test super strong gravity. Obviously, this cannot be done in laboratories on Earth. Central regions of black holes and neutron stars do have gravity sufficiently strong for such tests, but they are only several tens of kilometres across and typically observed from kiloparsecs away. Thus, they cannot be spatially resolved with current instruments. However, already existing technology (involving X-ray satellites in space) provides a very precise resolution in time of the observed variability of radiation coming from vicinity of black holes. This is why understanding the time behavior and oscillations of black hole accretion disks is so important.