News

On the scent of a supernova at the heart of the Galaxy

(10 February 2006)

Astrophysicists at Durham University are among an international team who have uncovered the trail of a 10,000 year old supernova at the heart of the Milky Way.

Using the H.E.S.S. telescopes in Namibia, they have been tracking gamma rays back to their source and have discovered high energy cosmic rays that have been through a cosmic accelerator – such as a supernova. They describe their findings in the latest edition of the science publication Nature (6th February 2006). Dr Paula Chadwick, Senior Lecturer in Physics at Durham, and one of about a dozen Durham researchers in the international team, said: “A supernova explosion that took place inside the gas clouds at the centre of the galaxy around 10,000 years ago, looks the most likely source of the gamma ray particles. While the original event was most likely hidden from view from Earth, we can now see its after-effects in a stream of particles that have been accelerated in the massive explosion.” The H.E.S.S. telescopes detect gamma rays, which are released when high energy particles known as cosmic rays collide with clouds of interstellar gas. Giant clouds of hydrogen gas, with more than 50 million times the mass of the Sun exist at the heart of the Milky Way (the galactic centre). Cosmic rays from here are more numerous and more energetic than those seen throughout the rest of the galaxy. Their numbers are particularly high at the higher energies. This suggests that they have been recently (astronomically speaking) accelerated to high energy, producing corresponding high energy gamma rays when they collide with the cloud material. This is the first time any facility has been sensitive enough to detect that the clouds glow with very high energy gamma rays. Candidates for such a cosmic accelerator are a stellar explosion (supernova) or a super-massive black hole. The H.E.S.S. team believe that their cosmic rays were created by a supernova that exploded in the last ten thousand years and is still producing a fading signal of new rays. Dr Jim Hinton, another British scientist involved in the discovery working at Heidelberg, concludes: "This is only the first step. We are of course continuing to point our telescopes at the centre of the Galaxy, and will work hard to pinpoint the exact acceleration site I'm sure that there are further exciting discoveries to come"