Magneto-rotational instability in magnetically polarized discs

Author:

Pimentel Diaz Oscar M12,Fragile P Chris23ORCID,Lora-Clavijo F D1,Ierace Bridget2,Bollimpalli Deepika24ORCID

Affiliation:

1. Escuela de Física, Universidad Industrial de Santander, A. A. 678, Bucaramanga 680002, Colombia

2. Department of Physics and Astronomy, College of Charleston, Charleston, SC 29424, USA

3. Kavli Institute for Theoretical Physics, University of California Santa Barbara, Santa Barbara, CA 93106, USA

4. Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, PL 00-716 Warsaw, Poland

Abstract

ABSTRACT The magneto-rotational instability (MRI) is the most likely mechanism for transportation of angular momentum and dissipation of energy within hot, ionized accretion discs. This instability is produced through the interactions of a differentially rotating plasma with an embedded magnetic field. Like all substances in nature, the plasma in an accretion disc has the potential to become magnetically polarized when it interacts with the magnetic field. In this paper we study the effect of this magnetic susceptibility, parameterized by χm, on the MRI, specifically within the context of black hole accretion. We find from a linear analysis within the Newtonian limit that the minimum wavelength of the first unstable mode and the wavelength of the fastest growing mode are shorter in paramagnetic (χm > 0) than in diamagnetic (χm < 0) discs, all other parameters being equal. Furthermore, the magnetization parameter (ratio of gas to magnetic pressure) in the saturated state should be smaller when the magnetic susceptibility is positive than when it is negative. We confirm this latter prediction through a set of numerical simulations of magnetically polarized black hole accretion discs. We additionally find that the vertically integrated stress and mass accretion rate are somewhat larger when the disc is paramagnetic than when it is diamagnetic. If astrophysical discs are able to become magnetically polarized to any significant degree, then our results would be relevant to properly interpreting observations.

Funder

COLCIENCIAS

Universidad Industrial de Santander

National Science Foundation

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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