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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

Moshoeshoe film screened at UFS as part of transformation programme
2004-10-14

A ground-breaking documentary film on the life and legacy of King Moshoeshoe I, the founder of the Basotho nation, will be screened at the University of the Free State (UFS) tonight (Wednesday 13 October 2004) at 19:00.

Rector and Vice-Chancellor of the UFS, prof. Frederick Fourie, said the UFS commissioned the documentary as a practical demonstration of the university’s commitment to the continued transformation of the campus and the creation of a new inclusive institutional culture for all staff and students.

It is part of a larger UFS project to honour the Moshoeshoe legacy of nation-building and reconciliation and to explore his role as a model of African leadership.

The documentary tells the life story of the legendary king, with emphasis on his remarkable leadership skills, his extraordinary talent for diplomacy and conflict resolution and his visionary commitment to creating a new nation from a fragmented society.

Almost all the filming was done on or around Moshoeshoe’s mountain stronghold, Thaba Bosiu.

The last part of the documentary explores the lessons for African leadership to be learnt from Moshoeshoe. The hour-long documentary film was produced by the well-known journalist Mr Max du Preez and was commissioned by the UFS as part of its centenary celebrations.

“Through this documentary film about King Moshoeshoe, the UFS commits itself to developing a shared appreciation of the history of this country,” said prof. Fourie.

“King Moshoeshoe was a great African statesman and leader. He was born in this region of the country, but his influence and legacy extends way beyond the borders of the Free State, Lesotho and even way beyond the borders of South Africa,” said prof. Fourie.

As part of the larger project, the UFS is investigating a possible annual Moshoeshoe memorial lecture that will focus on African leadership, nation-building and reconciliation, possible PhD-level research into the life and legacy of King Moshoeshoe and a literary anthology including prose and poetry.

“We must gain a deeper understanding of what really happened during his reign as king. Therefore the University of the Free State will encourage and support further research into the history, politics and sociology of the Moshoeshoe period, including his leadership style,” said prof. Fourie.

According to prof. Fourie the Moshoeshoe project will enable the UFS to give real meaning to respect for the diversity of our languages and cultures, and the unity South Africans seek to build as a democratic nation through such diversity.

According to the producer of the documentary, journalist Mr Max du Preez, the UFS deserves credit for recognising this extraordinary man and for financing this important documentary.

Du Preez said: “It was about time that South Africa rediscovered Moshoeshoe. Colonialist and Afrikaner Nationalist historians have painted him as a sly, untrustworthy and weak leader. Most historians have preferred to glorify leaders in South Africa’s past who were aggressors and conquerors. In the process most present-day South Africans came to regard Moshoeshoe as a minor tribal figure.”

“Yet this was the man who broke the cycle of violence, famine and suffering during the traumatic time in central South Africa in the early 1800s. During the entire 19th century, Moshoeshoe was virtually the only leader in South Africa who did not answer violence with violence, who did not set forth to conquer other groups and expand his land,” said Mr du Preez.

“I have no doubt that the stability that the Free State region has enjoyed over more than a century was largely due to Moshoeshoe’s leadership and vision. He can quite rightly be called “The Nelson Mandela of the 19th Century,” Mr du Preez added.

Explaining the title of the documentary film, Mr du Preez said: “We decided to call the documentary “The Reniassance King” because whichever way one looks at it, Moshoeshoe symbolised everything behind the concept of an African Renaissance.”

“He was progressive, just and fair; he deeply respected human life and dignity (we would nowadays call it human rights); he embraced modernity and technology without ever undermining his own people’s culture or natural wisdom; he never allowed European or Western influence to overwhelm him, make him insecure or take away his pride as an African,” said Mr du Preez.

“Moshoeshoe was the best of Africa. If only contemporary African leaders would follow his example of what African leadership should be,” Mr du Preez said.

Among the interviewees in the film were Lesotho’s most prominent historian, Dr LBBJ Machobane, the head of the UFS’s Department of History, prof. Leo Barnard, Moshoeshoe expert and Gauteng educationist Dr Peter Seboni, Lesotho author and historian Martin Lelimo and Chief Seeiso Bereng Seeiso, Principal Chief of Matsieng and direct descendant of the first King of the Basotho.

The documentary film on King Moshoeshoe will be screened on SABC 2 on Thursday 4 November 2004.
 

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