Origin of Cosmic Rays Revealed with Gamma Rays
PPARC Press Office
44 1793 442094
issued by the Particle Physics and Astronomy Research Council
November 4, 2004, Namibia -- A team of UK astronomers working with international partners has
produced the first ever image of an astronomical object using high
energy gamma rays, helping to solve a 100 year old mystery - an
origin of cosmic rays. Their research, published in the journal
Nature on November 4th, was carried out using the High Energy
Stereoscopic System (H.E.S.S.), an array of four telescopes, in
Namibia, South-West Africa.
The astronomers studied the remnant of a supernova that exploded
some 1,000 years ago, leaving behind an expanding shell of debris
which, seen from the Earth, is twice the diameter of the Moon. The
resulting image helps to solve a mystery that has been puzzling
scientists for almost 100 years - the origin of cosmic rays.
Cosmic rays are extremely energetic particles that continually
bombard the Earth, thousands of them passing through our bodies
every day. The production of gamma rays in this supernova shock
wave tells us that it is acting like a giant particle accelerator
in space, and thus a likely source of the cosmic rays in our
Dr Paula Chadwick of the University of Durham said "This picture
really is a big step forward for gamma-ray astronomy and the
supernova remnant is a fascinating object. If you had gamma-ray
eyes and were in the Southern Hemisphere, you could see a large,
brightly glowing ring in the sky every night."
Professor Ian Halliday, CEO of PPARC which funds UK participation
in H.E.S.S. said "These results provide the first unequivocal
proof that supernovae are capable of producing large quantities
of galactic cosmic rays - something we have long suspected, but
never been able to confirm."
Gamma rays are the most penetrating form of radiation we know,
around a billion times more energetic than the X-rays produced
by a hospital X-ray machine. This makes it very difficult to use
them to create an image - they just pass straight through any
surface which we might use to reflect them, for instance.
However, luckily for life on Earth, gamma rays from objects in
outer space are stopped by the atmosphere; when this happens, a
faint flash of blue light is produced, lasting for a few
billionths of a second. The astronomers used images of these
flashes of light, called Cherenkov radiation, to make a gamma
ray 'image' for the first time.
Notes for Editors
The H.E.S.S. collaboration
The High Energy Stereoscopic System (H.E.S.S.) team consists of
scientists from Germany, France, the UK, the Czech Republic,
Ireland, Armenia, South Africa and Namibia.
The H.E.S.S. array
Over the last few years, the H.E.S.S. collaboration have been
building a system of four telescopes in the Khomas Highland
region of Namibia, to study very-high-energy gamma rays from
cosmic particle accelerators. The telescopes, known as
Cherenkov telescopes, image the light created when high-energy
cosmic gamma rays are absorbed in the atmosphere, and have
opened a new energy domain for astronomy. The H.E.S.S.
telescopes each feature mirrors of area 107 square metres,
and are equipped with highly sensitive and very fast 960-pixel
light detectors in the focal planes. Construction of the
telescope system started in 2001; the fourth telescope was
commissioned in December 2003. Observations were being
made even while the system was being built, first using a single
telescope, then with two and three telescopes. While only the
complete four-telescope system provides the full performance,
the first H.E.S.S. telescope alone was already superior to any
of the instruments operated previously in the southern
hemisphere. Among the first targets to be observed with a two-
telescope instrument was the Galactic Centre.