Seminars

Giovedi 30 Marzo 2017, h. 11:30 
 Aula L. Rosino Dipartimento di Fisica e Astronomia

Elena Bannikova

  Institute of Radio Astronomy, National Academy of Sciences of Ukraine

 

Self-gravitating tori in astrophysical objects

 

ABSTRACT

 

Elena Yu. Bannikova and V.M.Kontorovich ,V.G.Vakulik, A.V.Sergeev, A.T.Kotvytskiy, N.А.Akerman
Institute of Radio Astronomy, National Academy of Science of Ukraine Karazin Kharkov National University

Toroidal (ring) structures occur in a manifold of astronomical objects: e.g. ring galaxies and dusty tori in AGNs. We examined the gravitational potential of a homogeneous circular torus, and proved that its outer potential can be represented with good accuracy by the potential of an infinitely thin ring. This simplification allowed us to treat the problem of particle motion in the gravitational field of a central mass and a torus, replacing the torus by a infinitely thin ring. In such system, there are “Lagrangian ring” and a region of unstable orbits, which can influence the distribution of the stars in ring galaxies. The stability of a self-gravitating torus with mass up to a few percent of the central mass was investigated in the framework of the N-body problem. We have shown that a thick torus is stable due to the motion of its particles in inclined orbits. The equilibrium cross-section has an oval shape with a Gaussian density distribution. The obtained results are used for the interpretation of the observed features of the obscuring tori in AGN.

Finally, we examined the gravitational lensing effects for a system in which the lens consists of a point mass and a homogeneous disc with a central hole. We have found a variety of cases in such system resulting in formation of one, two and three Einstein rings.

 

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