Energetics of Buchdahl stars and the magnetic Penrose process

Sanjar Shaymatov; Naresh Dadhich; Arman Tursunov

doi:10.1140/epjc/s10052-024-13419-9

2024 Impact factor 4.8

Particles and Fields

Open Access

Eur. Phys. J. C (2024) 84: 1015
https://doi.org/10.1140/epjc/s10052-024-13419-9

Regular Article - Theoretical Physics

Energetics of Buchdahl stars and the magnetic Penrose process

Sanjar Shaymatov¹^,2^,3^,4^a, Naresh Dadhich⁵^,6 and Arman Tursunov⁷^,8

¹ Institute for Theoretical Physics and Cosmology, Zhejiang University of Technology, 310023, Hangzhou, China
² Institute of Fundamental and Applied Research, National Research University TIIAME, Kori Niyoziy 39, 100000, Tashkent, Uzbekistan
³ Tashkent University of Applied Sciences, Gavhar Str. 1, 100149, Tashkent, Uzbekistan
⁴ Western Caspian University, AZ1001, Baku, Azerbaijan
⁵ Inter-University Centre for Astronomy and Astrophysics, (IUCAA), Post Bag 4, 411 007, Pune, India
⁶ Astrophysics Research Centre, School of Mathematics, Statistics and Computer Science, University of KwaZulu-Natal, Durban, South Africa
⁷ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121, Bonn, Germany
⁸ Research Centre for Theoretical Physics and Astrophysics, Institute of Physics, Silesian University in Opava, Bezručovo nám.13, 74601, Opava, Czech Republic

^a sanjar@astrin.uz

Received: 15 August 2024
Accepted: 23 September 2024
Published online: 7 October 2024

Abstract

Buchdahl star is the most compact object without an event horizon and is an excellent candidate for a black hole mimicker. Unlike black holes, rotating Buchdahl star can be over-extremal with respect to the black hole, sustaining a larger spin. We show that it can also develop an ergosphere above the threshold spin $β > 1 / \sqrt{2}$ $\beta > 1/\sqrt{2}$ , which allows extraction of its rotational energy. Electromagnetic field around Buchdahl star is also expected to differ from that of black hole in both strength and topology. In this paper, we explore the energetics of Buchdahl star focusing on the magnetic Penrose process in the two magnetic field configurations, i.e., uniform and dipole. Below the threshold spin, Buchdahl star is expected to be quiet, while above the threshold it can be much more efficient than the black hole if a dipolar magnetic field is developed on its surface.

© The Author(s) 2024

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