"In general, the objects in the universe that are very high-energy objects, or the processes that are high-energy processes, will radiate more in the short wavelength range towards the gamma rays or the x-rays"

This quote by Claude Nicollier is describing the electro-magnetic spectrum, which is the series of all possible frequencies of electro-magnetic radiation. The quote is saying that things or processes that are high-energy will produce more radiation in the short wavelength range, which includes gamma rays and x-rays. This is due to the fact that high-energy things and processes have more energy to emit in the type of radiation. Gamma rays and x-rays are the greatest energy kinds of electromagnetic radiation, and so they are the most likely to be produced by high-energy objects and processes. This is why gamma rays and x-rays are frequently used to study high-energy phenomena in deep space, such as black holes and supernovae.