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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

Names are not enough: a molecular-based information system is the answer
2016-06-03

Description: Department of Plant Sciences staff Tags: Department of Plant Sciences staff

Prof Wijnand Swart (left) from the Department of
Plant Sciences at the UFS and Prof Pedro Crous
from the Centraalbureau voor Schimmelcultures (CBS),
in the Netherlands.
Photo: Leonie Bolleurs

South Africa is the second-largest exporter of citrus in the world, producing 60% of all citrus grown in the Southern Hemisphere. It exports more than 70 % of its citrus crop to the European Union and USA. Not being able to manage fungal pathogens effectively can have a serious impact on the global trade in not only citrus but also other food and fibre crops, such as bananas, coffee, and cacao.

The Department of Plant Sciences at the University of the Free State (UFS) hosted a public lecture by Prof Pedro W. Crous entitled “Fungal Pathogens Impact Trade in Food and Fibre: The Need to Move Beyond Linnaeus” on the Bloemfontein Campus.

Prof Crous is Director of the world’s largest fungal Biological Resource Centre, the Centraalbureau voor Schimmelcultures (CBS), in the Netherlands. He is also one of the top mycologists in the world.

Since the topic of his lecture was very pertinent to food security and food safety worldwide, it was co-hosted by the Collaborative Consortium for Broadening the Food Base, a multi-institutional research programme managed by Prof Wijnand Swart in the Department of Plant Sciences.

Reconsider the manner in which pathogens are identified

Prof Crous stressed that, because international trade in products from agricultural crops will expand, the introduction of fungal pathogens to new regions will increase. “There is therefore an urgent need to reconsider the manner in which these pathogens are identified and treated,” he said.

According to Prof Crous, the older Linnaean system for naming living organisms cannot deal with future trade-related challenges involving pests and pathogens. A system, able to identify fungi based on their DNA and genetic coding, will equip scientists with the knowledge to know what they are dealing with, and whether it is a friendly or harmful fungus.

Description: The fungus, Botrytis cinerea Tags: The fungus, Botrytis cinerea

The fungus, Botrytis cinerea, cause of grey mould
disease in many fruit crops.
Photo: Prof Wijnand Swart

Embrace the molecular-based information system

Prof Crous said that, as a consequence, scientists must embrace new technologies, such as the molecular-based information system for fungi, in order to provide the required knowledge.

He presented this very exciting system which will govern the manner in which fungal pathogens linked to world trade are described. This system ensures that people from different countries will know with which pathogen they are dealing. Further, it will assist with the management of pathogens, ensuring that harmful pathogens do not spread from one country to another.

More about Prof Pedro Crous


Prof Crous is an Affiliated Professor at six international universities, including the UFS, where he is associated with the Department of Plant Sciences. He has initiated several major activities to facilitate global research on fungal biodiversity, and has published more than 600 scientific papers, many in high impact journals, and authored or edited more than 20 books.

 

 

Biography Prof Pedro Crous
Philosophical Transactions of the Royal Society B


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