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Article in prestigious Nature Astronomy sheds light on energy generation

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

Eye tracker device a first in Africa

2013-07-31

31 July 2013

Keeping an eye on empowerment

"If we can see what you see, we can think what you think."

Eye-tracking used to be one of those fabulous science-fiction inventions, along with Superman-like bionic ability. Could you really use the movement of your eyes to read people's minds? Or drive your car? Or transfix your enemy with a laser-beam?

Well, actually, yes, you can (apart, perhaps, from the laser beam… ). An eye tracker is not something from science fiction; it actually exists, and is widely used around the world for a number of purposes.

Simply put, an eye tracker is a device for measuring eye positions and eye movement. Its most obvious use is in marketing, to find out what people are looking at (when they see an advertisement, for instance, or when they are wandering along a supermarket aisle). The eye tracker measures where people look first, what attracts their attention, and what they look at the longest. It is used extensively in developed countries to predict consumer behaviour, based on what – literally – catches the eye.

On a more serious level, psychologists, therapists and educators can also use this device for a number of applications, such as analysis and education. And – most excitingly – eye tracking can be used by disabled people to use a computer and thereby operate a number of devices and machines. Impaired or disabled people can use eye tracking to get a whole new lease on life.

In South Africa and other developing countries, however, eye tracking is not widely used. Even though off-the-shelf webcams and open-source software can be obtained extremely cheaply, they are complex to use and the quality cannot be guaranteed. Specialist high-quality eye-tracking devices have to be imported, and they are extremely expensive – or rather – they used to be. Not anymore.

The Department of Computer Science and Informatics (CSI) at the University of the Free State has succeeded in developing a high-quality eye tracker at a fraction of the cost of the imported devices. Along with the hardware, the department has also developed specialised software for a number of applications. These would be useful for graphic designers, marketers, analysts, cognitive psychologists, language specialists, ophthalmologists, radiographers, occupational and speech therapists, and people with disabilities. In the not-too-distant future, even fleet owners and drivers would be able to use this technology.

"The research team at CSI has many years of eye-tracking experience," says team leader Prof Pieter Blignaut, "both with the technical aspect as well as the practical aspect. We also provide a multi-dimensional service to clients that includes the equipment, training and support. We even provide feedback to users.

"We have a basic desktop model available that can be used for research, and can be adapted so that people can interact with a computer. It will be possible in future to design a device that would be able to operate a wheelchair. We are working on a model incorporated into a pair of glasses which will provide gaze analysis for people in their natural surroundings, for instance when driving a vehicle.

"Up till now, the imported models have been too expensive," he continues. "But with our system, the technology is now within reach for anyone who needs it. This could lead to economic expansion and job creation."

The University of the Free State is the first manufacturer of eye-tracking devices in Africa, and Blignaut hopes that the project will contribute to nation-building and empowerment.

"The biggest advantage is that we now have a local manufacturer providing a quality product with local training and support."

In an eye-tracking device, a tiny infra-red light shines on the eye and causes a reflection which is picked up by a high-resolution camera. Every eye movement causes a change in the reflection, which is then mapped. Infra-red light is not harmful to the eye and is not even noticed. Eye movement is then completely natural.

Based on eye movements, a researcher can study cognitive patterns, driver behaviour, attention spans, even thinking patterns. A disabled person could use their eye-movements to interact with a computer, with future technology (still in development) that would enable that computer to control a wheelchair or operate machinery.

The UFS recently initiated the foundation of an eye-tracking interest group for South Africa (ETSA) and sponsor a biennial-eye tracking conference. Their website can be found at www.eyetrackingsa.co.za.

“Eye tracking is an amazing tool for empowerment and development in Africa, “ says Blignaut, “but it is not used as much as it should be, because it is seen as too expensive. We are trying to bring this technology within the reach of anyone and everyone who needs it.”

Issued by: Lacea Loader
Director: Strategic Communication

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