A simple model for hydromagnetic instabilities in the presence of a constant magnetic field

 

A. Sandoval-Villalbazo,¹ L. S. García-Colín, ^2,3 and A. Arrieta¹

 

¹ Departamento de Física y Matemáticas, Universidad Iberoamericana, Prolongación Paseo de la Reforma 880, Lomas de Santa Fé, 01210, Álvaro Obregón, México, D. F., México. (anabel.arrieta@uia.mx; alfredo.sandoval@uia.mx).

² Departamento de Física, Universidad Autónoma Metropolitana, Iztapalapa, 09340 México, D. F.

³ El Colegio Nacional, México, D. F., México.

 

Received 2004 March 15
Accepted 2005 January 31

 

RESUMEN

Se deduce la ecuación para la inestabilidad de Jeans en el caso de un plasma diluído completamente ionizado bajo la presencia de un campo gravitacional y otro campo magnético constante. Se obtiene un nuevo número de Jeans substancialmente modificado por la presencia del campo magnético bajo el supuesto de una simetría apropiada. No obstante, nuestro conocimiento actual respecto a la existencia de campos magnéticos primitivos en el universo es tal que, aparentemente, indica que son un tanto irrelevantes para la formación de estructuras en gran escala. Se presenta una estimación de la masa de Jeans considerando campos magnéticos cosmológicos.

 

ABSTRACT

In this paper we study a simple model consisting of a dilute fully ionized plasma in the presence of the gravitational and a constant magnetic field, so as to analyze the propagation of hydromagnetic instabilities. In particular we show that the so called Jeans instability is in principle affected by the presence of the magnetic field. A brief discussion is made attempting to assess this influence during the stage of the evolution of the Universe when structures were formed. The most logical conclusion is that if magnetic fields existed in those times then their magnitudes were too small to modify the Jeans mass. Our results place limits on the possible values of seed magnetic fields consistent with the formation of structures in the Universe. These values are within the range of the results obtained by other authors.

Key Words: Hydrodynamics — Magnetic fields — MHD — Instabilities.

 

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ACKNOWLEDGMENTS

This work was performed under grants from CONACyT 41081-F and 42809.

 

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