The XMM is the most powerful X-ray telescope ever launched. The most powerful X-ray telescope ever placed in orbit is about to be launched one third of the way to the moon.
Many celestial objects generate X-rays.
But Earth's atmosphere blocks out these X-rays. Its telescope mirrors are the most powerful ever developed in the world. The three 'mirror modules' have 58 wafer-thin mirrors each. The total mirror surface is bigger than a tennis court. And they are gold-plated.