Motion of spinning particles in non asymptotically flat spacetimes
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Regular Article - Theoretical Physics
Motion of spinning particles in non asymptotically flat spacetimes Bobir Toshmatov1,2,3,a , Ozodbek Rahimov2,b , Bobomurat Ahmedov2,3,c , Daniele Malafarina1,d 1
Department of Physics, Nazarbayev University, 53 Kabanbay Batyr, 010000 Nur-Sultan, Kazakhstan Ulugh Beg Astronomical Institute, Astronomicheskaya 33, 100052 Tashkent, Uzbekistan 3 Tashkent Institute of Irrigation and Agricultural Mechanization Engineers, Kori Niyoziy 39, 100000 Tashkent, Uzbekistan
2
Received: 4 June 2020 / Accepted: 16 July 2020 © The Author(s) 2020
Abstract The assumption of asymptotic flatness for isolated astrophysical bodies may be considered an approximation when one considers a cosmological context where a cosmological constant or vacuum energy is present. In this framework we study the motion of spinning particles in static, spherically symmetric and asymptotically non-flat spacetimes with repulsive cosmological vacuum energy and quintessential field. Due to the combined effects of gravitational attraction and cosmological repulsion, the region where stable circular orbits are allowed is restricted by an innermost and an outermost stable circular orbits. We show that taking into account the spin of test particles may enlarge or shrink the region of allowed stable circular orbits depending on whether the spin is co-rotating or counter-rotating with the angular momentum of the particles.
1 Introduction Our current confidence in the existence of astrophysical black holes relies on the ability of mathematical model to describe observations. This is true for the gravitational wave signals observed from binary black hole mergers [1,2] as well as for the observational evidence based on electromagnetic radiation coming from accretion disks surrounding the black holes [3] like for example in the case of the Event Horizon Telescope (EHT) collaboration’s image of the supermassive black hole at the center of the galaxy M87 [4]. All the theoretical models used to describe the observables obtained from accretion disks rely on the mathematical description of the motion of test particles and viscous plasma fluid in the surroundings of the black hole candidate. However, the motion of test particles may be influenced by a e-mail:
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a large number of factors, including, for example, the geometry [5–8], the presence of external fields [9,10], the spin of the particles [11–15] and possible deviations from classical general relativity [16,17]. In particular, when describing astrophysical isolated bodies one is usually led to consider asymptotically flat spacetimes. This is the result of the assumption that every other gravitational influence on the astrophysical object can be neglected. However, in a cosmological context this assumption may not hold as we may have to take into account the effects of the cosmological constant. It is well kn
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