We had a very interesting talk from Dr Roberta Zanin from Bologna in Italy about The Cherenkov Telescope Array Observatory: a new eye on the most extreme Universe. Jim Nisbet reviews the talk for us:

The Cherenkov Effect has been known about for many years, where electromagnetic radiation is produced by charged particles moving through a medium faster than the speed of light in that medium. Gamma rays and cosmic rays from distant objects can produce cascades of charged particles and radiation when they reach the Earth’s atmosphere which can then be detected by ground-based equipment. The use of Cherenkov Radiation in astronomy means that an observatory is not directly observing astronomical phenomena, rather the result of interactions with the atmosphere – not dissimilar from the principle of using a big tank of ‘cleaning fluid’ to measure solar neutrino flux. And unlike many astronomical observations the Earth’s atmosphere is actually an essential part of the detection process, so this type of astronomy could not be done from space.

The international Cherenkov Telescope Array Observatory (CTAO) project will see two observatories, one based at La Palma and the other in Chile therefore providing whole sky coverage. Each site will see a range of telescope sizes – small, medium and large – to allow measurement of gamma rays across a broad energy spectrum, and configured in such a way to capture as many events as possible, to give accurate directional and energy information. The Northern Hemisphere array will have 13 telescopes and focus on extra-Galactic science whereas the array in the Southern Hemisphere will have 51 telescopes focusing on Galactic science.

Gamma rays are produced by the most extreme phenomena in the Universe, such as supernova remnants, active galactic nuclei, collisions of neutron stars, so observing Cherenkov radiation will help understand what happens in these events. It might also shed light on the one hundred year old mystery of cosmic rays, where current supernova remnant evidence doesn’t fully explain higher energy rays. The CTAO is expected to provide a step change in very high energy gamma ray astronomy to give a greater in-depth understanding of known objects and their mechanisms, the discovery of new object classes and – in what was described as the fun part – the inevitable unexpected observations which they have not yet thought about.

Jim Nisbet