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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

21 Icons: 21 Years of Freedom Collection at the University of the Free State
2015-09-02

   

In Prayer and Protest - Sophia Williams De Bruyn

The Johannes Stegmann Art Gallery, in partnership with 21 Icons, is hosting the 21 Years of Freedom Collection, an exhibition specially curated for the University of the Free State.
21 Icons celebrates a heroic past and inspires a hopeful future. The project was launched in 2013 as an initiative that uses film, photography and written narrative to celebrate the lives of extraordinary South Africans. It highlights people who have been catalysts in shaping society, on a local or global level and across a variety of contexts: in a social, political, environmental or artistic sense.

It is the brainchild of internationally renowned photographer and filmmaker Adrian Steirn, whose primary source of inspiration was the life of Nelson Mandela. In one way or another, all of the men and women featured in the project have extended his legacy, making a magnificent impact on South Africa and beyond.

  

Beautiful Sacrifice - Albie Sachs

21 Years of Freedom features 21 icons from the first and second seasons of the project. It includes the last official photographic portrait of Nelson Mandela and many of his friends and fellow struggle heroes. Behind each portrait lies a carefully planned concept that captures the essence of each icon, capturing their spirit and distinct legacy.

Among the other extraordinary South Africans featured in this collection, are struggle icons Ahmed Kathrada and Advocate George Bizos, Archbishop Desmond Tutu, human rights and environmental activist Kumi Naidoo, celebrated storyteller Gcina Mhlophe, Nobel laureate Nadine Gordimer, activist and musician Yvonne Chaka Chaka, gender activist Sophia Williams De Bruyn and artist William Kentridge.

    

The Full Report - Zubeida Jaffer

The 21 Icons was created as a movement for positive change. By sharing the stories of iconic South African men and women, the intention is to inspire new generations to follow in their footsteps.  With the country celebrating 21 years of democracy but still grabbling with injustices, the message that everyone can do something to make a difference, is portrayed in these powerful and inspiring stories.

Writer-in-residence and well-respected journalist, Zubeida Jaffer, who features among the collection of 21 striking photographs, opened the exhibition saying, “I feel like I’m surrounded by a circle of energy from which I have been fortunate to draw strength …It’s a choice that we make…whether to draw energy from those who are positive and forward looking or to surround ourselves with people who are fearful.  There is a lot to be fearful about in our country. We have lived through very fearful and difficult times.  But to cope with these times, those people and many others have kept their focus on hope.  They have kept their focus on what is possible…and what we would like South Africa to be in the future.”

For more information on 21 Icons: 21 Years of Freedom Collection contact the Johannes Stegmann Art Gallery at +27 (0)51 401 2706 or dejesusav@ufs.ac.za

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