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Non-equatorial deflection of light due to Kerr–Newman black hole: a material medium approach.

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Title: Non-equatorial deflection of light due to Kerr–Newman black hole: a material medium approach.
Authors: Roy, Saswati1 (AUTHOR) sr.phy2011@yahoo.com, Kala, Shubham2 (AUTHOR) shubhamkala871@gmail.com, Ghosh, Prasanjit1 (AUTHOR) prasanjitghosh699@gmail.com, Nandan, Hemwati3 (AUTHOR) hnandan@associates.iucaa.in, Sen, Asoke K.4 (AUTHOR) asokesen@yahoo.com
Source: European Physical Journal C -- Particles & Fields. Aug2025, Vol. 85 Issue 8, p1-21. 21p.
Subjects: Deflection (Light), Spacetime, Kerr black holes, Refractive index, Kerr electro-optical effect
Abstract: We explored the effect of space-time geometry on the trajectory of light rays in the context of a charged, rotating black hole. We derived an analytical expression for the deflection of light rays in Kerr–Newman space-time geometry, using a material medium approach, on non-equatorial plane. From this deflection angle expression it is evident that the charge and rotation of the black hole can affect the light rays' paths. For Kerr–Newman geometry, the deflection angle decreases with increasing charge when the rotation parameter is held constant. Conversely, for a constant charge, the deflection angle increases with the rotation parameter for prograde and decreases for retrograde trajectories. Applying both factors results in the deflection angle being lower than that of the Schwarzschild geometry. Non-equatorial study of the deflection angle reveals that it is maximum in the equatorial plane than in the pole. The frame-dragging effects in the Kerr–Newman field were taken into account to calculate the velocity of light rays, leading to the determination of the refractive index in this field geometry. This study concludes that, depending on the values of the rotation parameter and charge parameter, both prograde and retrograde trajectories coincide, result in that at some point the frame dragging effect is the same for prograde and retrograde motion. Also, the frame dragging effect increases towards poles than the equatorial plane, and this nontrivial nature results because of the interplay between charge, rotation parameter and rotation frequency of the black hole. [ABSTRACT FROM AUTHOR]
Copyright of European Physical Journal C -- Particles & Fields is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Non-equatorial deflection of light due to Kerr–Newman black hole: a material medium approach.
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  Data: <searchLink fieldCode="AR" term="%22Roy%2C+Saswati%22">Roy, Saswati</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> sr.phy2011@yahoo.com</i><br /><searchLink fieldCode="AR" term="%22Kala%2C+Shubham%22">Kala, Shubham</searchLink><relatesTo>2</relatesTo> (AUTHOR)<i> shubhamkala871@gmail.com</i><br /><searchLink fieldCode="AR" term="%22Ghosh%2C+Prasanjit%22">Ghosh, Prasanjit</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> prasanjitghosh699@gmail.com</i><br /><searchLink fieldCode="AR" term="%22Nandan%2C+Hemwati%22">Nandan, Hemwati</searchLink><relatesTo>3</relatesTo> (AUTHOR)<i> hnandan@associates.iucaa.in</i><br /><searchLink fieldCode="AR" term="%22Sen%2C+Asoke+K%2E%22">Sen, Asoke K.</searchLink><relatesTo>4</relatesTo> (AUTHOR)<i> asokesen@yahoo.com</i>
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  Data: <searchLink fieldCode="JN" term="%22European+Physical+Journal+C+--+Particles+%26+Fields%22">European Physical Journal C -- Particles & Fields</searchLink>. Aug2025, Vol. 85 Issue 8, p1-21. 21p.
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  Data: <searchLink fieldCode="DE" term="%22Deflection+%28Light%29%22">Deflection (Light)</searchLink><br /><searchLink fieldCode="DE" term="%22Spacetime%22">Spacetime</searchLink><br /><searchLink fieldCode="DE" term="%22Kerr+black+holes%22">Kerr black holes</searchLink><br /><searchLink fieldCode="DE" term="%22Refractive+index%22">Refractive index</searchLink><br /><searchLink fieldCode="DE" term="%22Kerr+electro-optical+effect%22">Kerr electro-optical effect</searchLink>
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  Data: We explored the effect of space-time geometry on the trajectory of light rays in the context of a charged, rotating black hole. We derived an analytical expression for the deflection of light rays in Kerr–Newman space-time geometry, using a material medium approach, on non-equatorial plane. From this deflection angle expression it is evident that the charge and rotation of the black hole can affect the light rays' paths. For Kerr–Newman geometry, the deflection angle decreases with increasing charge when the rotation parameter is held constant. Conversely, for a constant charge, the deflection angle increases with the rotation parameter for prograde and decreases for retrograde trajectories. Applying both factors results in the deflection angle being lower than that of the Schwarzschild geometry. Non-equatorial study of the deflection angle reveals that it is maximum in the equatorial plane than in the pole. The frame-dragging effects in the Kerr–Newman field were taken into account to calculate the velocity of light rays, leading to the determination of the refractive index in this field geometry. This study concludes that, depending on the values of the rotation parameter and charge parameter, both prograde and retrograde trajectories coincide, result in that at some point the frame dragging effect is the same for prograde and retrograde motion. Also, the frame dragging effect increases towards poles than the equatorial plane, and this nontrivial nature results because of the interplay between charge, rotation parameter and rotation frequency of the black hole. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: <i>Copyright of European Physical Journal C -- Particles & Fields is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1140/epjc/s10052-025-14659-z
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      – Code: eng
        Text: English
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        Type: general
      – SubjectFull: Spacetime
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      – SubjectFull: Kerr black holes
        Type: general
      – SubjectFull: Refractive index
        Type: general
      – SubjectFull: Kerr electro-optical effect
        Type: general
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      – TitleFull: Non-equatorial deflection of light due to Kerr–Newman black hole: a material medium approach.
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            NameFull: Roy, Saswati
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              Text: Aug2025
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