27 July 2012
A few minutes past midnight on 26 July, the largest Cherenkov telescope ever built blinked open to gaze at the Namibian sky. Named HESS II, the giant telescope’s 600-tonne bulk and 28-metre mirror will survey the southern hemisphere, hunting for violent, high-energy cosmic sources such as supermassive black holes, supernovae and pulsars.
Cherenkov telescopes search for signs of very-high-energy gamma rays by watching forCherenkov radiation – a scatter of charged particles produced from gamma-ray interactions in our atmosphere and captured as faint flashes of blue light. HESS II captures these flashes with a camera around a million times as fast as one you or I might own.
There are currently two other operating Cherenkov systems – MAGIC, in the Canary Islands and VERITAS, in Arizona. The HESS array includes four smaller telescopes, each with a 12-metre mirror. HESS II has an “unprecedented” resolving ability, says the team, enabling it to capture a sharper picture of the skies.
Gamma-ray observations from HESS will be used in combination with data from the Square Kilometre Array (SKA), the world’s largest radio telescope system, expected to begin observing in 2020. Comprising telescopes scattered across South Africa, Australia and New Zealand, the SKA will be sensitive enough to detect the equivalent of an airport radar on a planet 50 light years away.