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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

Media: Sunday Times
2006-05-20

Sunday Times, 4 June 2006

True leadership may mean admitting disunity
 

In this edited extract from the inaugural King Moshoeshoe Memorial Lecture at the University of the Free State, Professor Njabulo S Ndebele explores the leadership challenges facing South Africa

RECENT events have created a sense that we are undergoing a serious crisis of leadership in our new democracy. An increasing number of highly intelligent, sensitive and committed South Africans, across class, racial and cultural spectrums, confess to feeling uncertain and vulnerable as never before since 1994.

When indomitable optimists confess to having a sense of things unhinging, the misery of anxiety spreads. We have the sense that events are spiralling out of control and that no one among the leadership of the country seems to have a definitive handle on things.

There can be nothing more debilitating than a generalised and undefined sense of anxiety in the body politic. It breeds conspiracies and fear.

There is an impression that a very complex society has developed, in the last few years, a rather simple, centralised governance mechanism in the hope that delivery can be better and more quickly driven. The complexity of governance then gets located within a single structure of authority rather than in the devolved structures envisaged in the Constitution, which should interact with one another continuously, and in response to their specific settings, to achieve defined goals. Collapse in a single structure of authority, because there is no robust backup, can be catastrophic.

The autonomy of devolved structures presents itself as an impediment only when visionary cohesion collapses. Where such cohesion is strong, the impediment is only illusory, particularly when it encourages healthy competition, for example, among the provinces, or where a province develops a character that is not necessarily autonomous politically but rather distinctive and a special source of regional pride. Such competition brings vibrancy to the country. It does not necessarily challenge the centre.

Devolved autonomy is vital in the interests of sustainable governance. The failure of various structures to actualise their constitutionally defined roles should not be attributed to the failure of the prescribed governance mechanism. It is too early to say that what we have has not worked. The only viable corrective will be in our ability to be robust in identifying the problems and dealing with them concertedly.

We have never had social cohesion in South Africa — certainly not since the Natives’ Land Act of 1913. What we definitely have had over the decades is a mobilising vision. Could it be that the mobilising vision, mistaken for social cohesion, is cracking under the weight of the reality and extent of social reconstruction, and that the legitimate framework for debating these problems is collapsing? If that is so, are we witnessing a cumulative failure of leadership?

I am making a descriptive rather than an evaluative inquiry. I do not believe that there is any single entity to be blamed. It is simply that we may be a country in search of another line of approach. What will it be?

I would like to suggest two avenues of approach — an inclusive model and a counter-intuitive model of leadership.

In an inclusive approach, leadership is exercised not only by those who have been put in some position of power to steer an organisation or institution. Leadership is what all of us do when we express, sincerely, our deepest feelings and thoughts; when we do our work, whatever it is, with passion and integrity.

Counter-intuitive leadership lies in the ability of leaders to read a problematic situation, assess probable outcomes and then recognise that those outcomes will only compound the problem. Genuine leadership, in this sense, requires going against probability in seeking unexpected outcomes. That’s what happened when we avoided a civil war and ended up with an “unexpected” democracy.

Right now, we may very well hear desperate calls for unity, when the counter-intuitive imperative would be to acknowledge disunity. A declaration of unity where it manifestly does not appear to exist will fail to reassure.

Many within the “broad alliance” might have the view that the mobilising vision of old may have transformed into a strategy of executive steering with a disposition towards an expectation of compliance. No matter how compelling the reasons for that tendency, it may be seen as part of a cumulative process in which popular notions of democratic governance are apparently undermined and devalued; and where public uncertainty in the midst of seeming crisis induces fear which could freeze public thinking at a time when more voices ought to be heard.

Could it be that part of the problem is that we are unable to deal with the notion of opposition? We are horrified that any of us could be seen to have become “the opposition”. The word has been demonised. In reality, it is time we began to anticipate the arrival of a moment when there is no longer a single, overwhelmingly dominant political force as is currently the case. Such is the course of history. The measure of the maturity of the current political environment will be in how it can create conditions that anticipate that moment rather than seek to prevent it. We see here once more the essential creativity of the counter-intuitive imperative.

This is the formidable challenge of a popular post-apartheid political movement. Can it conceptually anticipate a future when it is no longer overwhelmingly in control, in the form in which it is currently, and resist, counter-intuitively, the temptation to prevent such an eventuality? Successfully resisting such an option would enable its current vision and its ultimate legacy to our country to manifest in different articulations, which then contend for social influence. In this way, the vision never really dies; it simply evolves into higher, more complex forms of itself. Consider the metaphor of flying ants replicating the ant community by establishing new ones.

We may certainly experience the meaning of comradeship differently, where we will now have “comrades on the other side”.

Any political movement that imagines itself as a perpetual entity should look at the compelling evidence of history. Few movements have survived those defining moments when they should have been more elastic, and that because they were not, did not live to see the next day.

I believe we may have reached a moment not fundamentally different from the sobering, yet uplifting and vision-making, nation-building realities that led to Kempton Park in the early ’90s. The difference between then and now is that the black majority is not facing white compatriots across the negotiating table. Rather, it is facing itself: perhaps really for the first time since 1994. Could we apply to ourselves the same degree of inventiveness and rigorous negotiation we displayed leading up to the adoption or our Constitution?

This is not a time for repeating old platitudes. It is the time, once more, for vision.

In the total scheme of things, the outcome could be as disastrous as it could be formative and uplifting, setting in place the conditions for a true renaissance that could be sustained for generations to come.

Ndebele is Vice-Chancellor of the University of Cape Town and author of the novel The Cry of Winnie Mandela

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