An European Space Agency (ESA) led effort is all set to use silicon technology to enable astronomy’s clearest X-ray view yet of the most violent regions of space.
“ESA has been working with specialist European firms to develop this new optical technique and build up a supporting industry,” said Marcos Bavdaz, Head of ESA’s Advanced Technology Section. “This ‘silicon pore optics’ effort is part of the Agency’s preparation for the International X-ray Observatory (IXO), a candidate mission with NASA and Japan’s space agency for around 2020,” he said. Observing the sky in X-rays reveals a violent Universe of exploding stars, black holes and incandescent gas clouds. With temperatures of millions of degrees, such high-energy objects shine at X-ray wavelengths, but not in visible light. Astronomers could only study this violent, high-energy Universe once the space age gave them a way of placing telescopes above the X-ray-absorbing atmosphere. Standard optical designs do not work because energetic X-rays are reflected only at extremely shallow angles. While visible light reflects off a mirror like a ball bouncing off a wall, X-ray reflection works more like a stone skimming along a pond. Telescope mirrors must face sideways instead of straight on, and many mirrors are needed to gather sufficient X-rays. So, an X-ray telescope is more like a set of Russian dolls, with mirrors stacked around each other.
ESA’s XMM-Newton X-ray space observatory uses more than 250 gold-coated nickel mirrors, while NASA’s Chandra relies on fewer mirrors made of heavier glass. For IXO, the aim is to boost XMM’s collecting area 20-fold, while delivering three times the resolution. Achieving this demands new technology. While NASA is investigating an alternative called ‘slumped glass’, ESA is focusing on silicon pore optics, based around commercial silicon wafers. According to ESA’s Eric Wille, “Manufacturers already polish these wafers to optical quality to better ‘print’ the tiny structures needed for the latest microprocessors. So, the wafers need no further polishing, while also being both light and stiff.” The next step is to streamline the assembly process for mass production and further improve quality, opening the door to unprecedented discoveries in the X-ray sky.