A method that uses laser frequency combs to calibrate astronomical spectrographs to unprecedented accuracies has been developed and successfully tested by researchers in Europe. The method could be used to find Earth-sized exoplanets by detecting their tiny influence on the motions of their companion stars. The comb was tested on the European Southern Observatory’s High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph at the La Silla Observatory in Chile.
Astronomical spectrographs separate light according to wavelength and the spectra that they produce play important roles in many aspects of astronomy. As a result, astronomers are constantly looking at ways to make their spectrographs more accurate, stable and precisely calibrated. Currently, the best spectrographs, such as HARPS, use thorium-argon lamps or iodine cells for calibration – however, these do not deliver the precision to detect the tiny shifts in the wavelength of starlight caused by the presence of an exoplanet.