Stacks of carefully polished, coated and cut silicon wafers – normally used to manufacture integrated circuits – that will focus X-rays inside ESA’s Athena space observatory, due for launch in 2028.
Invisible X-rays tell us about the very hot matter in the Universe – black holes, supernovas and superheated gas clouds. But energetic X-rays do not behave like typical light waves – try to reflect them with a standard mirror and they are absorbed. Instead, X-rays can only be reflected at shallow angles, like stones skimming across water.
That means multiple mirrors must be stacked together to build a telescope. ESA has developed ‘silicon pore optics’ to see much further into space than the ageing XMM-Newton X-ray observatory.
This approach is based on industrial silicon wafers, taking advantage of their stiffness and super-polished surface. Grooves are cut into the wafers to form pores through which the X-rays are focused. A few dozen at a time are stacked together to form a single mirror module. Many hundreds of these modules will be combined to form the optics of the X-ray mission.
To find out more, check our video interview with ESA optics engineer Eric Wille.