Cosmology in South Africa

This paper reviews research in theoretical cosmology in South Africa, providing an overview of the work that has been done and the groups involved in that work.     

Molecular signature of star formation at high redshifts

In recent years there has been much debate, both observational and theoretical, about the nature of star formation at high redshift. In particular, there seems to be strong evidence of a greatly enhanced star formation rate early in the Universe’s evolution. Simulations investigating the nature of the first stars indicate that these were large, with masses in excess of 100 solar masses. By the use of a chemical model, we have simulated the molecular signature of massive star formation for a range of redshifts, using different input models of metallicity in the early Universe. We find that, as long as the number of massive stars exceeds that in the Milky Way by factor of at least 1000, then several ‘hot-core’ like molecules should have detectable emission. Although we predict that such signatures should already be partly detectable with current instruments (e.g. with the VLA), facilities such as ALMA will make this kind of observation possible at the highest redshifts.     

Nonconservation of baryons in cosmology—revisited

The concept of the steady-state universe discussed by Hoyle & Narlikar two decades ago is revived in the light of the present discussions of the phase transition in the early big-bang universe. It is shown that with suitable scaling the bubble universe solution bears a striking similarity to the inflationary scenarios being discussed today. The currently discussed idea of cosmic baldness was also anticipated in the C-field cosmology of the steady-state universe. An erratum to this article is available at .     

The Design and Realization of the Payload Integrated Test System for DAMPEtwo

The Dark Matter Particle Explorer (DAMPE) is a space-borne high-energy cosmic ray detector. The payload consists of five subsystems, including the Plastic Scintillator Detector (PSD), the Silicon-Tungsten tracKer converter detector (STK), the BGO (Bismuth Germanate) calorimeter, the NeUtron Detector (NUD), and the Data AcQuisition system (DAQ). The five subsystems work collaboratively to collect the information of cosmic rays. In order to systematically verify the performance of the payload before launching, we have developed a set of integrated test system for the ground tests of the payload based on the LabWindows/CVI (C programming language Virtual Instrument) platform. This system has realized the integrity and automation of the comprehensive ground tests of the payload, improved the security, reliability, and efficiency of the ground tests, and provided a guarantee for the successful delivery of the payload.     

Superstrings and cosmology

We discuss some aspects of superstring cosmology. Especially, the influence of winding strings on the compactification scenario is emphazised. It is shown that torus compactified superstrings could improve the compactification behaviour.     

由SLOAN观测数据测试大尺度结构的均匀性

宇宙学的基本假设之一是宇宙在大尺度上均匀各向同性.为了验证星系分布在大尺度上的均匀性,分别计算观测样本和观测空间几何体的分形维数,得到SDSS-DR4中星系分布的分形维数.观测空间几何体的分形维数用随机样本来确定.样本中的星系红移z的范围为0.01-0.26.当尺度持续增加至几十个Mpc时,星系分布的分形维数一致地趋向于3.所有的样本均显示了明显的转变尺度,当尺度大于此转变尺度时,星系分布的分形维数D<,G>～3,星系的分布转变为均匀分布.结果支持了宇宙学的基本原理关于宇宙大尺度均匀的假设.样本的转变尺度随着样本的光度增强而变大,说明小尺度上星系的分布不是简单的分形分布,而是多维分形分布.高光度星系的转变尺度非常大,直到100h-1Mpc左右才变得均匀.     

The Dark UNiverse Explorer (DUNE): proposal to ESA’s cosmic vision

The Dark UNiverse Explorer (DUNE) is a wide-field space imager whose primary goal is the study of dark energy and dark matter with unprecedented precision. For this purpose, DUNE is optimised for the measurement of weak gravitational lensing but will also provide complementary measurements of baryonic accoustic oscillations, cluster counts and the Integrated Sachs Wolfe effect. Immediate auxiliary goals concern the evolution of galaxies, to be studied with unequalled statistical power, the detailed structure of the Milky Way and nearby galaxies, and the demographics of Earth-mass planets. DUNE is an Medium-class mission which makes use of readily available components, heritage from other missions, and synergy with ground based facilities to minimise cost and risks. The payload consists of a 1.2 m telescope with a combined visible/NIR field-of-view of 1 deg². DUNE will carry out an all-sky survey, ranging from 550 to 1600 nm, in one visible and three NIR bands which will form a unique legacy for astronomy. DUNE will yield major advances in a broad range of fields in astrophysics including fundamental cosmology, galaxy evolution, and extrasolar planet search. DUNE was recently selected by ESA as one of the mission concepts to be studied in its Cosmic Vision programme.

Some critiques of the big bang cosmology

Still more shocking than the metaphysical assumption of some initial singularity, is the constant insistence upon the so-called cosmological principle of “homogeneity” and “isotropy” of the Universe. Observations do contradict this principle. And to me, the inhomogeneous, fractal at least on a certain scale range, of the distribution of matter is in itself an important cosmological fact, hitherto almost neglected. Moreover difficultties as to the applicability of the second principle of thermodynamics, observations of abnormal redshifts, etc., are casting large doubts not only upon the standard cosmological models, but even on the interpretation of the observed redshift as due solely to a universal expansion.