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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

Ghanaian academic speaks about next generation of African scholars
2013-10-08

 

Attending the seminar were from left: Adv Erika Cilliers, Sisa Mlonyeni (both from the Office of the Public Protector), Prof Adomako Ampofo and Prof Heidi Hudson, Head of the Centre for Africa Studies.
Photo: Jerry Mokoroane
08 October 2013

Prof Akosua Adomako Ampofo, one of the Centre for Africa Studies’newly-appointed advisory board members, addressed students and staff on 3 October 2013. Her topic Are you the scholar Africa needs?enthralled the audience with the passionate way in which she argued for nurturing activist-scholars rather than scholars who simply produce knowledge for the sake of it. “It is more urgent than ever before that … we do not simply see our roles as researchers and teachers, but that we are committed to impacting our communities” for the better – also by “making our knowledge production globally visible,” she argued. Africa is said to contribute less than 0.5 percent of the world’s scientific publications. The fact that most of these – and nearly all of the social science production – emanate from just three nations (Egypt, Nigeria and South Africa) means that many countries are absent from the radar.

According to her, the next generation of African scholars will have to compete within a hostile terrain where private universities are proliferating and costs of higher education are on the rise. These scholars will have to possess 22nd century skills, but a 20th century heart and sensitivity for the continent and its people.

Drawing on Kwame Nkrumah, Prof Ampofo proposed three guiding principles for becoming the scholars Africa needs. Firstly, by having a passion for knowledge as well as an Africa-centred knowledge – “nobody can tell our stories better than we can.”. Secondly, to translate our research into outputs not only in the form of internationally-recognised publications, but also in popular sources that will be read by a much wider public. And lastly, to carrying the torch for teaching and learning in the classroom – preparing our students to serve Africa or, as Nkrumah said, producing “devoted men and women with imagination and ideas, who, by their life and actions, can inspire our people to look forward to a great future.”.

Akosua Adomako Ampofo is a Professor of African and Gender Studies, and Director of the Institute of African Studies at the University of Ghana, Legon. An activist-scholar, her current work addresses African knowledge systems; race, ethnicity and identity politics; gender-based expressions of violence; constructions of masculinities; women and work; and popular culture. She is currently co-editing a volume titled, Transatlantic Feminisms: Women and Gender in Africa and the African Diaspora.In 2010, she was awarded the Sociologists for Women in Society Feminist Activism Award.


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