CTA Science in a Nutshell
Radiation at gamma-ray energies differs fundamentally from that detected at lower energies: GeV to TeV gamma-rays cannot conceivably be generated by thermal emission from hot celestial objects. The energy of thermal radiation reflects the temperature of the emitting body, and apart from the Big Bang there is nothing hot enough in the known Universe to emit such gamma-rays.
Instead, we find that high-energy gamma-rays probe a "non-thermal" Universe, where other mechanisms allow the concentration of large amounts of energy onto a single quantum of radiation.
In a bottom-up fashion, gamma-rays can be generated when highly relativistic particles - accelerated for example in the gigantic shock waves of stellar explosions - collide with ambient gas, or interact with photons and magnetic fields. The flux and energy spectrum of the gamma-rays reflects the flux and spectrum of the high-energy particles. They can therefore be used to trace these cosmic rays and electrons in distant regions of our own Galaxy or even in other galaxies.
High-energy gamma-rays can also be produced in a top-down fashion by decays of heavy particles such as the hypothetical dark matter particles or cosmic strings, both relics which might be left over from the Big Bang. Therefore, gamma-rays provide a window to the discovery of the nature and constituents of dark matter.
Galactic Gamma-Ray Sources
Extragalactic Gamma-Ray Sources
Several recent papers discuss in detail the science capabilities of next-generation VHE gamma-ray telesopes such as CTA. These include: