CTA will eventually consist of over 100 telescopes distributed over two locations: CTA-S in Chile on the ESO Paranal site, and CTA-N on the island of La Palma. Together they will cover the entire sky. CTA will also be an order of magnitude better than the current gold standard, H.E.S.S., in most metrics, achieved by using an array of three sizes of telescopes, from 4 meter diameter (small-sized telescopes, or SSTs) to massive 23m large-size telescopes (LSTs), with 12m class medium-sized telescopes in between (MSTs). Each telescope class is sensitive to a different energy band between 10s of GeV to 100s of TeV. Optimising the desired number of each type and their location to achieve the best results while keeping cost down is one of CTA’s primary challenges. The large number of telescopes serves two goals: 1) achieve the highest possible sensitivity by maximising atmospheric sky coverage, and 2) improve the angular resolution by detecting Cherenkov events with as many telescopes as possible to more accurately triangulate. Current facilities like VERITAS, H.E.S.S and MAGIC employ only two to five telescopes each. As the effective area of the observatory is set by the area of the sky covered by the telescopes on the ground, CTA will have the largest effective area of any gamma-ray telescope built, and thus significantly outperform the current state-of-the-art facilities. Construction of CTA-N has already started and for CTA-S it will start in 2021.
Each telescope will collect data from individual airshowers, which will be further analysed off line in order to separate gamma-ray induced airshowers from the differently shaped airshowers caused by cosmic rays. The amount of data collected will be very large. The data will be collected, processed, and distributed by the CTA Data Management Center (DMC) at Desy, Zeuthen (Germany). CTA is a Big Science Data facility, with a yearly rate of 20 PB of science-quality data. Manpower hired by the CTA Observatory will be located at four locations: CTA-N (La Palma), CTA-S (Chile), CTA headquarters in Bologna, Italy, and at the DMC in Zeuthen. Further processing of data will be done by the community of scientists involved in CTA.
CTA is an important facility for the relatively new discipline of ""multi-messenger"" physics, which is a multi-disciplinary field in between physics and astronomy. In multi-messenger physics one combines electromagnetic signals with other messengers, such as cosmic rays (highly energetic particles that reach Earth' from outside the solar system), high-energy neutrinos, and gravitational waves. The astrophysical sources that generate these signals are invariably very energetic and violent, and include sources such as supernovae and their products, accreting neutron stars and black holes, and merging neutron stars and black holes. Although gamma-rays are electromagnetic signals, the photon energies are comparable to those of cosmic rays. In fact both gamma-rays and neutrinos are created when cosmic rays collide with atoms and low-energy photons. Cosmic rays are, therefore, the common origin of high-energy neutrinos and gamma rays. As cosmic rays are charged particles, they not travel in straight paths. To understand the origin of cosmic rays, and observe their creation sites, we rely on the gamma-ray and neutrino signals produced in the cosmic-ray sources of origin. Neutrinos are notoriously difficult to detect, so for accurate, high-signal-to-noise measurements gamma rays are key.
In addition to cosmic-ray related gamma rays, certain types of dark matter particles, so-called WIMP dark matter, will generate gamma rays when dark-matter self-annihilates. These gamma rays will have a predictable energy spectrum, and are expected to be generated by dense dark-matter structures, such as the Galactic center, and clusters of galaxies. CTA will be the first facility sensitive enough to probe the predicted self-annihilation rate of WIMP dark matter.