X-rays are part of the electromagnetic spectrum with a wavelength of between 0.1-10 nm in length and were founded in 1895 by Wilhelm Roentgen. Though x-rays are actually waves they act more like particles due to the extremely small size of their wavelength.
Wierdly anything which is hotter than a million degrees will emit x-rays. This means that the sun gives off x-rays into space as well as certain stars. Though x-rays can be used in telescopes, the most important use of x-rays is in the medical industry for diagnostic methods.
I find x-ray pretty cool, as it was discovered completely by chance, and is now is used worldwide in medicine, and even referred to in comic books.
It seems that most of the accidental science discoveries are the discoveries which become the most important to our everyday lives!
Explorer fact: In some German speaking countries X-rays are called Roentgen rays.