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Astronomers in the UK, the US and Germany are the first to use a new data-analysis technique that could boost a telescope’s ability to search for “exoplanets” — planets outside our solar system. Surprisingly, the technique makes clever use of the diffraction of light, an effect that had previously prevented telescopes from resolving many exoplanets from their parent stars. The astronomers used the technique to get a combined image and spectrum of a faint star 48 light-years away (Astrophys. J. in press).

Looking for exoplanets is tricky – normally, they cannot be observed directly with telescopes because any light they emit is drowned out by the glare from their parent star. In the last decade or so, however, astronomers have realized that they can observe them in special circumstances – for example, when an exoplanet’s orbit takes it behind its parent star so we no longer see the contribution of its light, causing the star to “wink”.

Astronomers wishing to observe a planet nearby to a star must also contend with the “diffraction limit”, which is a well-known limitation on the spatial resolution of an optical telescope. Even in the best telescopes, as light passes through the aperture it will diffract, causing alternating light and dark concentric rings – called “Airy rings” – to surround high-resolution images of stars and other objects. The radii of these rings depend on the wavelength of the light being observed, and no object can be seen that is smaller than the spot that appears at the centre of them.