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Modified virial theorem for highly magnetized white dwarfs

Mukhopadhyay, B and Sarkar, A and Tout, CA (2021) Modified virial theorem for highly magnetized white dwarfs. In: Monthly Notices of the Royal Astronomical Society, 500 (1). pp. 763-771.

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Official URL: https://doi.org/10.1093/mnras/staa3136


Generally the virial theorem provides a relation between various components of energy integrated over a system. This helps us to understand the underlying equilibrium. Based on the virial theorem we can estimate, for example, the maximum allowed magnetic field in a star. Recent studies have proposed the existence of highly magnetized white dwarfs (B-WDs), with masses significantly higher than the Chandrasekhar limit. Surface magnetic fields of such white dwarfs could be more than 10⁹ G with the central magnitude several orders higher. These white dwarfs could be significantly smaller in size than their ordinary counterparts (with surface fields restricted to about 10⁹ G). In this paper, we reformulate the virial theorem for non-rotating B-WDs in which, unlike in previous formulations, the contribution of the magnetic pressure to the magnetohydrostatic balance cannot be neglected. Along with the new equation of magnetohydrostatic equilibrium, we approach the problem by invoking magnetic flux conservation and by varying the internal magnetic field with the matter density as a power law. Either of these choices is supported by previous independent work and neither violates any important physics. They are useful while there is no prior knowledge of field profile within a white dwarf. We then compute the modified gravitational, thermal, and magnetic energies and examine how the magnetic pressure influences the properties of such white dwarfs. Based on our results we predict important properties of these B-WDs, which turn out to be independent of our chosen field profiles. © 2021 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.

Item Type: Journal Article
Publication: Monthly Notices of the Royal Astronomical Society
Publisher: Oxford University Press
Additional Information: The copyright for this article belongs to the Author.
Keywords: magnetic fields – MHD – stars: general – stars: magnetic field – stars: massive – white dwarfs.
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 23 Dec 2021 11:20
Last Modified: 23 Dec 2021 11:20
URI: http://eprints.iisc.ac.in/id/eprint/67955

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