Cosmology studies the origin and evolution of the universe as a whole, as well as the formation, distribution, and evolution of large-scale structure in it, using physical (and mathematical) principles. The underlying theory on which modern physical cosmology is based is General Relativity theory (GR), which was formally presented by Albert Einstein in 1915.
The standard cosmological model (often referred to as the ΛCDM model) assumes that, on large scales (scales larger than individual galaxies), the universe is homogeneous and isotropic and has been expanding since its origin in the big bang some 13.8 billion years ago. It also assumes that the universe went through an extremely short early-period accelerated expansion (known as cosmological inflation), followed by radiation-dominated and then matter-dominated epochs and a currently undergoing late-time accelerated expansion. It further assumes that, at present, the universe consists of around 70% dark energy responsible for the late-time accelerated expansion, about 30% matter (of which about 80% exists in the form of dark matter) and a negligible amount of radiation.
The overarching theme of the Cosmology group’s research is modified gravitation and cosmology, and involves trying to understand the existence and nature of dark matter and dark energy - the aforementioned components of the matter-energy content of the universe not
well explained by, and definitely not well understood in the context of, GR. In this vein, our research efforts and interests include: the cosmological implications of generalisations to GR (such as f(R), f(T), f(Q) models of gravitation), both from the point of view of background dynamics and large-scale structure formation. Other aspects of our research involve introducing extra matter fields (such as in the scalar field and Chaplygin gas cosmological models) and interacting dark-fluid cosmological models that mimic early dark matter and late-time dark energy domination scenarios. We study the viability of these deviations from the standard cosmological model using theoretical consistency analysis of the background field equations and the cosmological perturbations, as well using available and simulated astronomical data to constrain the parameter space of the models.
Part of our envisaged research activities involve SKA science which, among other things, includes studying the nature and constraints of dark energy, strong-field tests of gravity (such as using pulsars and black holes), and cosmological magnetogenesis.
Another area of interest is the study of the formation of the very first stars as well as the ionisation of the intergalactic medium by these very first stars. This period is termed the Epoch of Reionisation (EoR), and it is one of the least-known areas in cosmology from an observational point of view. Currently, several cosmological models are still predicting different reionisation scenarios. Thus, more sensitive data is required to discriminate between them. Radio Interferometric arrays such as the Hydrogen Epoch of Reionization Array (South Africa) and the Murchison Widefield interferometer (SKA-low, Australia) are amongst the purposely built radio interferometers dedicated to providing these sensitive data products. Ongoing research areas at the Centre include the testing of cosmological models, modelling of antenna response and the analysis of systematic errors in data products.
Researchers: Amare Abebe, Thato Tsabone, Ntsikelelo Charles, Olebogeng Tlhapane
Current postdocs: Shambel Sahlu, Renier Hough
Current students: Carissa de Klerk, Edmund Kyazze, Moemedi Mmutle, Olebogeng Tlhapane, Rethabile Thubisi, Robert Rugg
PhD: Dumiso Mithi, Thato Tsabone