A Self-Guided Tour of the Electromagnetic Spectrum
It's not easy to imagine how high the frequency of a high-energy gamma ray is. During the time it takes for its wave to go through one cycle, a gamma-ray wave traveling at the speed of light will travel only the width of a proton, a tiny particle found within the nucleus of an atom.
Gamma rays are created throughout the universe in violent explosions. On Earth, they originate from the decay of radioactive elements and within particle accelerators, which are devices that smash together subatomic particles propelled at velocities close to the speed of light.
Like ultraviolet radiation and X-rays, gamma rays can kill microorganisms and are used to sterilize food and other objects, such as medical instruments and equipment. Gamma radiation is also a treatment for cancer.
High-energy gamma-ray photons are relatively scarce, and it takes many photons to create a meaningful image of an object in space. For this reason, there are not many images of astronomical objects in gamma wavelengths. This one, a gamma-ray image of the entire sky as seen from earth, took 18 months to create.