DUT Open Scholar
https://openscholar.dut.ac.za:443
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.2024-08-15T09:52:33ZThe role of dimension and electric charge on a collapsing geometry in Einstein–Gauss–Bonnet gravity
https://hdl.handle.net/10321/5415
Title: The role of dimension and electric charge on a collapsing geometry in Einstein–Gauss–Bonnet gravity
Authors: Brassel, Byron P.
Abstract: The analysis of the continual gravitational contraction of a spherically symmetric
shell of charged radiation is extended to higher dimensions in Einstein–Gauss–Bonnet
gravity. The spacetime metric, which is of Boulware–Deser type, is real only up to a
maximumelectric charge and thus collapse terminates with the formation of a branch
singularity. This branch singularity divides the higher dimensional spacetime into two
regions, a real and physical one, and a complex region. This is not the case in neutral
Einstein–Gauss–Bonnetgravityaswellasgeneralrelativity. The charged gravitational
collapse process is also similar for all dimensions N ≥ 5 unlike in the neutral scenario
where there is a marked difference between the N = 5 and N > 5 cases. In the
case where N = 5uncharged collapse ceases with the formation of a weaker, conical
singularity which remains naked for a time depending on the Gauss–Bonnet invariant,
beforesuccumbingtoaneventhorizon.Thesimilarityofchargedcollapseforallhigher
dimensionsisauniquefeatureinthetheory.Thesufficientconditionsfortheformation
of anakedsingularity are studied for the higher dimensional charged Boulware–Deser
spacetime. For particular choices of the mass and charge functions, naked branch
singularities are guaranteed and indeed inevitable in higher dimensional Einstein
Gauss–Bonnet gravity. The strength of the naked branch singularities is also tested
andit is found that these singularities become stronger with increasing dimension, and
no extension of spacetime through them is possible.2024-03-01T00:00:00ZRadiating composite stars with electromagnetic fields
https://hdl.handle.net/10321/5414
Title: Radiating composite stars with electromagnetic fields
Authors: Maharaj, Sunil D.; Brassel, Byron P.
Abstract: We derive the junction conditions for a general spherically symmetric radiating star with an electromagnetic field across a comoving surface. The interior consists of a charged composite field containing barotropic matter, a null dust and a null string fluid. The exterior atmosphere is described by the generalised Vaidya spacetime. We generate the boundary condition at the stellar surface showing that the pressure is determined by the interior heat flux, anisotropy, null density, charge distribution and the exterior null string density. A new physical feature that arises in our analysis is that the surface pressure depends on the internal charge distribution for generalised Vaidya spacetimes. It is only in the special case of charged Vaidya spacetimes that the matching interior charge distribution is equal to the exterior charge at the surface as measured by an external observer. Previous treatments, for neutral matter and charged matter, arise as special cases in our treatment of composite matter.2021-09-01T00:00:00ZRadiating stars with composite matter distributions
https://hdl.handle.net/10321/5413
Title: Radiating stars with composite matter distributions
Authors: Maharaj, Sunil D.; Brassel, Byron P.
Abstract: In this paper we study the junction conditions for a generalised matter distribution in a radiating star. The internal matter distribution is a composite distribution consisting of barotropic matter, null dust and a null string fluid in a shear-free spherical spacetime. The external matter distribution is a combination of a radiation field and a null string fluid. We find the boundary condition for the composite matter distribution at the stellar surface which reduces to the familiar Santos result with barotropic matter. Our result is extended to higher dimensions. We also find the boundary condition for the general spherical geometry in the presence of shear and anisotropy for a generalised matter distribution.2021-04-01T00:00:00ZGeneralised radiating fields in Einstein-Gauss-Bonnet gravity
https://hdl.handle.net/10321/5412
Title: Generalised radiating fields in Einstein-Gauss-Bonnet gravity
Authors: Brassel, Byron P.; Maharaj, Sunil D.
Abstract: A five-dimensional spherically symmetric generalised radiating field is studied in Einstein–Gauss–Bonnet gravity. We assume the matter distribution is an extended Vaidya-like source and the resulting Einstein–Gauss–Bonnet field equations are solved for the matter variables and mass function. The evolution of the mass, energy density and pressure are then studied within the spacetime manifold. The effects of the higher order curvature corrections of Einstein–Gauss–Bonnet gravity are prevalent in the analysis of the mass function when compared to general relativity. The effects of diffusive transport are then considered and we derive the specific equation for which diffusive behaviour is possible. Gravitational collapse is then considered and we show that collapse ends with a weak and conical singularity for the generalised source, which is not the case in Einstein gravity.2020-10-20T00:00:00Z