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Modal analysis of gravitational instabilities in nearly Keplerian, counter-rotating collisionless discs

Gulati, Mamta and Saini, Tarun Deep (2017) Modal analysis of gravitational instabilities in nearly Keplerian, counter-rotating collisionless discs. In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 465 (2). pp. 2505-2516.

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Official URL: http://dx.doi.org/10.1093/mnras/stw2780


We present a modal analysis of instabilities of counter-rotating, self-gravitating collisionless stellar discs, using the recently introduced modified WKB formulation of spiral density waves for collisionless systems by Gulati & Saini. The discs are assumed to be axisymmetric and in coplanar orbits around a massive object at the common centre of the discs. The mass in both discs is assumed to be much smaller than the mass of the central object. For each disc, the disc particles are assumed to be in near circular orbits. The two discs are coupled to each other gravitationally. The perturbed dynamics of the discs evolves on the order of the precession time-scale of the discs, which is much longer than the Keplerian time-scale. We present results for the azimuthal wavenumber m = 1 and 2, for the full range of disc mass ratio between the prograde and retrograde discs. The eigenspectra are in general complex, therefore all eigenmodes are unstable. Eigenfunctions are radially more compact for m = 1 as compared to m = 2. Pattern speed of eigenmodes is always prograde with respect to the more massive disc. The growth rate of unstable modes increases with increasing mass fraction in the retrograde disc, and decreases with m; therefore, m = 1 instability is likely to play the dominant role in the dynamics of such systems.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the OXFORD UNIV PRESS, GREAT CLARENDON ST, OXFORD OX2 6DP, ENGLAND
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 03 Apr 2017 04:48
Last Modified: 03 Apr 2017 04:48
URI: http://eprints.iisc.ac.in/id/eprint/56444

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