A new way of bending X-rays raises the prospect of smaller, more powerful X-ray space telescopes. Based on technology originally developed for medical imaging machines, Stacked Prism Lens are being developed by a team led by Mats Danielsson and astrophysicist Mark Pearce at KTH Royal Institute of Technology, Stockholm, that replace conventional mirrors with a network of micro-engineered plastic prisms.
The X-ray band of the spectrum has become an important tool for studying the universe. Space telescopes like NASA's Chandra X-Ray Observatory have provided invaluable data about various high-energy phenomena, like black holes and supernovae, that have greatly improved our understanding of the formation and dynamics of stars and galaxies.
Unfortunately, X-ray telescopes have a number of disadvantages. For one thing, X-rays can't penetrate the Earth's atmosphere, so the telescopes have to be sent into space. They also have real problems with resolution and focal length.
Because X-rays pass through matter, they can't be reflected or refracted like visible light or radio waves, so they're hard to focus. So, instead of having lenses or reflectors, X-ray telescopes use a set of nested, cylindrical mirrors that focus the X-rays by making them bend at a very shallow angle. It's a practical solution, but it isn't very high resolution and requires a very long focal length – for example, Chandra's comes out to 10 m (33 ft).
According to KTH, the Stacked Prism Lens technology, which uses an array of small plastic prisms to bend X-rays at a slightly higher angle than conventional mirrors, drastically reduces the focal length of the telescope to under 50 cm (20 in).
"This allows you to build a telescope that can collect more than a thousand times as much light as today's X-ray space telescopes can handle," says Danielsson says. "Another advantage is that it will have good spatial resolution, which means that you can see more details in the pictures you take. This is important in order to make correct physical interpretations."
This means that the next generation of X-ray telescopes can be smaller and lighter, making them cheaper to send into space and able to see much farther and with greater clarity. The team says that this will open up the possibility of discovering new, distant objects and addressing many basic questions about the universe.
So far, KTH has developed a laboratory prototype of the new telescope and is currently working on improving the design of the lenses and associated sensors, mechanics and electronics in anticipation to building a proof-of-concept telescope, which will be sent into space for testing.
The new technology was first revealed in Nature Astronomy.
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