News

High Energy Mystery lurks at the Galactic Centre

(22 September 2004)

A mystery lurking at the centre of our own Milky Way galaxy – an object radiating high-energy gamma rays – has been detected by an international team of astronomers including staff from Durham University.

Their research, published in the Journal Astronomy and Astrophysics, was carried out using the High Energy Stereoscopic System (HESS), an array of four telescopes, in Namibia, South-West Africa.

The Galactic Centre harbours a number of potential gamma-ray sources, including a supermassive black hole, remnants of supernova explosions and possibly an accumulation of exotic ‘dark matter’ particles, each of which should emit the radiation slightly differently. The radiation observed by the HESS team comes from a region very near Sagittarius A*, the black hole at the centre of the galaxy. According to most theories of dark matter, it is too energetic to have been created by the annihilation of dark matter particles. The observed energy spectrum best fits theories of the source being a giant supernova explosion, which should produce a constant stream of radiation.

Dr Paula Chadwick of the University of Durham said: “We know that a giant supernova exploded in this region 10,000 years ago. Such an explosion could accelerate cosmic gamma rays to the high energies we have seen – a billion times more energy than the radiation used for X-rays in hospitals. But further observations will be needed to determine the exact source.”

Professor Ian Halliday, Chief Executive of the Particle Physics and Astronomy Research Council (PPARC) which funds UK involvement in HESS said: “Science continues to throw out the unexpected as we push back the frontiers of knowledge.” Halliday added “The centre of our Galaxy is a mysterious place, home to exotic phenomena such as a black hole and dark matter. Finding out which of these sources produced the gamma-rays will tell us a lot about the processes taking place in the very heart of the Milky Way.”

However, the team’s theory doesn’t fit with earlier results obtained by the Japanese /Australian CANGAROO instrument HESS has now done, making it harder to deduce the source. These previous results have different characteristics to the HESS observations. It is possible that the gamma-ray source at the Galactic Centre varies over the timescale of a year, suggesting that the source is in fact a variable object, such as the central black hole.

The HESS team hopes to unravel the mystery with further observations of the Galactic Centre over the next year or two. The full array of four telescopes will be inaugurated on 29 September 29 2004, see http://www.mpi-hd.mpg.de/hfm/HESS/public/HESS_broschuere_04_c.pdf for further details.

ends

Notes for Editors

The full scientific paper can be seen at http://www.edpsciences.org/articles/aa/abs/2004/37/contents/contents.html.

The HESS collaboration
The High Energy Stereoscopic System (HESS) team consists of scientists from Germany, France, the UK, the Czech Republic, Ireland, Armenia, South Africa and Namibia.

The HESS array
Over the last few years, the HESS 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 HESS 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 HESS. 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.

Contacts:

Dr Paula Chadwick
Department of Physics
University of Durham
Phone: +44 191 334 3560
Email: p.m.chadwick@durham.ac.uk

Julia Maddock
PPARC Press Office
Tel +44 1793 442094
Mobile +44 7901 514 975
Email: Julia.maddock@pparc.ac.uk

Tom Fennelly
University of Durham PR Office
Tel +44 191 334 6078
Email: t.p.fennelly@durham.ac.uk

Images:

High resolution Galactic centre pictures at .
Project images at http://www.mpi-hd.mpg.de/hfm/HESS/public/full_images/full_images.htm.

For further information, see the project website a href="http://www.mpi-hd.mpg.de/HESS.

The Particle Physics and Astronomy Research Council (PPARC) is the UK’s strategic science investment agency. It funds research, education and public understanding in four broad areas of science - particle physics, astronomy, cosmology and space science.

PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Organisation for Nuclear Research, CERN, the European Space Agency and the European Southern Observatory. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.

PPARC's Public Understanding of Science and Technology Awards Scheme provides funding to both small local projects and national initiatives aimed at improving public understanding of its areas of science.