SCIENCE & TECHNOLOGY
SA joins search for gamma-rays
3 September 2002
The world's most sensitive gamma-ray telescopes were inaugurated in
Namibia on 3 September. The High Energy Stereoscopic System (HESS), a
European/African collaboration in which South Africa and Namibia are
partners, will look for gamma rays produced by the most energetic
particles in the universe.
The First Light Ceremony of the HESS (High Energy Stereoscopic System) telescope will be organised by the Unit of Space Physics, Potchefstroom University and the Physics Department of the University of Namibia.
South Africa's participation in HESS is being sponsored by the Department of Science and Technology and funded by the National Research Foundation, and also involves the SA Institute of Physics and the South African Astronomical Observatory.
South Africa has already spent R30-million on construction of the telescopes, and will inject a further R5-million a year into the Namibian economy for the 10-year duration of the
project.
Namibia is an excellent site scientifically, one of the best in the world
for ground-based optical astronomy, with ideal atmospheric conditions
for the techniques used by HESS. However, it has also presented a
huge challenge - the site at Goellschau in the Khomas Highland of Namibia has limited road access, and special water, power and computer connections had to be put in place.
The array will initially consist of four telescopes, the first of which
will become operational on September 3. This telescope alone is more
sensitive than any other existing ground-based array or telescope working
in this particular area of the electromagnetic spectrum.
Once all four telescopes are operational by late 2003, researchers will
use HESS to investigate a range of extreme cosmic environments, such as the
supernova remnants formed when a star dies.
A major goal is to see if these remnants are a source of cosmic rays - charged particles that constantly
bombard the earth from space. The origin of cosmic rays is difficult to determine, as they are influenced by the magnetic field of our galaxy. However, the gamma rays they emit travel in a straight line, so they may reveal the primary source of the cosmic rays.
HESS will also be probing the structure of pulsars - rapidly rotating stars, formed when a massive star explodes at the end of its life, which emit pulses across the range of the electromagnetic spectrum - and active galactic nuclei to find the
source of their energy.
Professor Christo Raubenheimer of the Potchefstroom team explains: "HESS
is set to give us unique insights into some of the most extreme environments in the universe.
"We have some expectations about what we will be able learn - more about supernova remnants, active galaxies and so on - but experience tells us that when you improve the sensitivity of your telescope, you see things you never expected as well. It's going to be very exciting! We
will also be able to test our understanding of nature under ultra-extreme conditions."
When gamma rays are absorbed by the earth's atmosphere, pairs of electrons
and positrons are created and emit tiny flashes of light in a process
known as Cherenkov radiation. Telescopes such as HESS can detect these
tiny flashes of light.
By using the earth's atmosphere as part of the detector, the telescopes have much greater sensitivity than an equivalent space-based device, and can detect far fainter gamma ray sources than previously possible.
Gamma rays are usually produced by particles moving very rapidly. The
study of gamma rays enables astronomers to learn more about systems that
accelerate these particles, such as active galactic nuclei, where
supermassive black holes produce jets of particles travelling near the
speed of light. Gamma rays can also be produced by the annihilation of massive
particles that may be the source of the 'missing mass' in the
universe.
Gamma rays are a type of electromagnetic radiation, like optical light or
radio waves. Electromagnetic waves have a wide range of wavelengths
and can be used to see different views of objects. Visible light only
shows us what is on the surface, but other types of electromagnetic waves can reveal more, like the X-rays used by doctors to see broken bones.
In their quest to understand our universe, astronomers branched out long ago from visible light to examine objects that radiate in the microwave and X-ray
wavelengths. However, gamma rays, the most energetic kind of electromagnetic wave, have remained difficult to use until now, as there are very few strong sources for astronomers to view.
HESS stands for High Energy Stereoscopic System, but the HESS array is also named after Viktor Hess, who received the 1936 Nobel Prize in Physics for his discovery of cosmic radiation.
Source: Potchefstroom
University
| 
