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28 October 2019 | Story Leonie Bolleurs | Photo Anja Aucamp
Dr Brain van Soelen and Prof Pieter Meintjies
UFS scientists, Prof Pieter Meintjes and Dr Brian van Soelen, are part of the prestigious H.E.S.S. collaboration that recently published in Nature Astronomy.

Think of an object with a mass exceeding that of the Sun, squeezed into a volume of a sphere with the radius of a city like Bloemfontein. This very dense, compact object, known as a pulsar, is also a great source of energy. According to Physics Professor, Prof Pieter Meintjes, this pulsar (neutron star produced in supernova explosion) is also a key element of a recently submitted paper in Nature Astronomy.

Prof Meintjes and Dr Brian van Soelen, Senior Lecturer, both from the Department of Physics at the University of the Free State (UFS), were part of the High Energy Stereoscopic System (H.E.S.S.) collaboration of 220-plus scientists worldwide who worked on the paper Resolving the Crab pulsar wind nebula at tera-electronvolt energies, published in the prestige journal Nature Astronomy. 

According to Prof Meintjes, the fact that the paper was accepted for publication in Nature Astronomy testifies of the importance of this finding in the high-energy astrophysics community.

Powerful generators of electricity

He elaborates on the study: “The name pulsar originates from the fact that rotating neutron stars produced in supernova explosions produce beams of radiation, much like a lighthouse. Every time the beam intersects the observer’s line of sight, the observer receives a pulse of radiation.”

“As a result of this enormous mass squeezed into a small volume, these objects have the same density as that of an atomic nucleus. These objects (very dense pulsars) spin very rapidly and have enormous magnetic fields; for example, the pulsar at the centre of the Crab Nebulae spins around its axis once every 33 milliseconds (millisecond: one thousandth of a second) and possesses a magnetic field strength of the order of one tera-Gauss (tera – million x million). For comparison, the average strength of the Earth’s magnetic field is 0.5. Gauss and the magnetic field strength on the Sun ranges between 1 000 and 4 000 Gauss.”

“Because of this very super-strong rapid-spinning magnet, enormous electric fields are induced that can accelerate particles such as electrons and protons to energies in excess of one tera-electronvolt (optical light that are emitted by an ordinary lightbulb has energies of the order of one electronvolt).”

Prof Meintjes continues: “This means that these fast-rotating neutron stars are extraordinary powerful generators of electricity, which fills the surrounding cloud (supernova remnant) with super-high energy-charged particles that can produce, in turn, very high energy gamma rays through various processes such as synchrotron radiation and inverse-Compton radiation, to name a few.”

H.E.S.S. collaboration 

Above one tera-electronvolt, the gamma rays are detected by huge ground-based telescopes such as H.E.S.S., utilising the Earth’s atmosphere.

“When these high-energy gamma rays enter the atmosphere, they produce showers of super-relativistic particles that produce Cherenkov light – detected by the telescope. The technique is called the Atmospheric Cherenkov Technique (ACT).”

HESS
The High Energy Stereoscopic System. (Photo: Supplied)

“The H.E.S.S. gamma-ray collaboration is but one collaboration that has studied this source intensively over the past couple of decades or so.  Being the most powerful gamma-ray telescope facility currently operational, very careful analysis of the data managed to reveal that the gamma-ray emitting region inside the nebula is about 10 times bigger in size than the region where the x-rays are emitted within the nebula.” 

“This has solved a long-standing question as to how big the gamma-ray emitting region within these supernova remnants are, compared to the region where the x-rays, for example, originates,” says Prof Meintjes. 

Both Prof Meintjes and Dr Van Soelen are members of this prestigious H.E.S.S. collaboration. Their participation in this project, together with scientists from universities such as the University of Oxford, the University of Leicester, and the University of Bordeaux, opens up valuable research opportunities for UFS postgraduate students to enter the international stage and interact with the best scientists in the world.

They are also members of the editorial board responsible for the internal review of research papers before being submitted to more prestigious journals, for example, Nature Astronomy. Dr Van Soelen is also a coordinator of multi-wavelength follow-up observations within the H.E.S.S. collaboration. 

This is the second time that Prof Meintjes published in Nature Astronomy. Previously, he was co-author of a paper on emission from a white dwarf pulsar, showing that fast-rotating white dwarf stars could in fact mimic emission from neutron star pulsars. He developed the theoretical model reported in that paper, explaining the multi-wavelength emission from radio to X-ray energies.


News Archive

UFS hosts consortium to discuss broadening subcontinent’s food base
2017-03-14

Description: Cactus Tags: Cactus

The Steering Committee of the Collaborative
Consortium for Broadening the Food Base comprises,
from the left: Prof Wijnand Swart (UFS),
Dr Sonja Venter (ARC) and Dr Eric Amonsou (DUT).
Photo: Andrè Grobler

There is huge pressure on the agricultural industry in southern Africa to avert growing food insecurity. One of the ways to address this is to broaden the food base on the subcontinent via crop production. Climate change, urbanisation, population growth, pests and diseases continually hamper efforts to alleviate food insecurity. Furthermore, our dependence on a few staple crops such as maize, wheat, potatoes, and sunflower, serve to exacerbate food insecurity.  

Broadening the food base  
To address broadening the food base in southern Africa, scientists from the University of the Free State (UFS), the Durban University of Technology (DUT) and the Agricultural Research Council (ARC) have formed a Collaborative Consortium for the development of underutilised crops by focusing on certain indigenous and exotic crops. The Consortium met at the UFS this week for two days (6, 7 March 2017) to present and discuss their research results. The Principal Investigator of the Consortium, Prof Wijnand Swart of the Department of Plant Sciences in the Faculty of Natural and Agricultural Sciences, said awareness had risen for the need to rescue and improve the use of orphan crops that were up to now, for the most part, left aside by research, technological development, and marketing systems.  

"Many indigenous southern African
plant grains, vegetables and tubers
have the potential to provide a variety
of diets and broaden the household
food base.”

Traditional crops Generally referred to as alternative, traditional or niche crops, five crops are being targeted by the Consortium, namely, two grain legumes, (Bambara groundnut and cowpea), amaranthus (leaf vegetable), cactus pear or prickly pear and amadumbe (a potato-like tuber). Swart said these five crops would play an important role in addressing the food and agricultural challenges of the future. “Many indigenous southern African plant grains, vegetables and tubers have the potential to provide a variety of diets and broaden the household food base.” The potential of the many so-called underutilised crops lies not only in their hardiness and nutritional value but in their versatility of utilisation. "It may be that they contain nutrients that can be explored to meet the demand for functional foods," said Swart.

Scientific institutions working together
The Collaborative Consortium between the three scientific institutions is conducting multi-disciplinary research to develop crop value chains for the five underutilised crops mentioned above. The UFS and ARC are mainly involved in looking at production technologies for managing crop environments and genetic technologies for crop improvement. The DUT is focusing on innovative products development and market development.  

 

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