The AstroComb from Menlo Systems GmbH is analyzing starlight from the European Southern Observatory’s Very Large Telescope (VLT) in Chile. Tilo Steinmetz, Menlo’s AstroComb product manager, inspects the comb modes of the ESPRESSO-AstroComb that are projected onto a screen by means of an echelle spectrograph. Courtesy of Menlo Systems GmbH. ESO engineers and astrophysicists have succeeded in combining the light collected by each of the observatory’s four main telescopes and directing it into the newly developed ESPRESSO spectrograph for analysis. Feeding all the light into a single instrument gives astronomers access to information that was not previously available. The ability to merge the light from all four of the VLT’s 8.2-m mirrors into a single image makes the VLT into the largest optical telescope in the world, in terms of light-collecting surface area. Menlo’s AstroComb is used to enhance the precision with which light can be analyzed. The AstroComb is a frequency comb, which is a collection of tens of thousands of equidistantly spaced laser lines. Each line is made up of light of a known frequency, defined in respect to a basic frequency standard, such as an atomic clock or the GPS. As a result, frequency combs can be used to measure single frequencies with extremely high accuracy. For the calibration of the new spectrograph at ESO, the frequency comb is generated and fed into the ESPRESSO instrument in parallel with the collected starlight. Both the starlight and the frequency comb are then separated into their spectral components by passage through a very large diffraction grating and projected onto a CCD-based camera, revealing the individual teeth of the comb, which can then be used like a ruler to assign precise frequencies to the absorption lines in the spectrum of the starlight. Astrophysicists plan to use the ESPRESSO spectrograph to search for and characterize Earth-like exoplanets. With the AstroComb, they are now in a position to detect minimal shifts in the spectral lines of stars. Dynamic changes of this sort can disclose whether a given star actually hosts planets — and they can be used to determine the orbital periods of exoplanets, their distances from their parent star, and their sizes. Astronomers will also use ESPRESSO to observe quasars. In addition, researchers hope to investigate whether the constants of nature are in fact constant. All of these quests require observational techniques that combine great precision and sensitivity with extreme robustness to external perturbations. “We are very pleased to have contributed to sharpening our view of the universe,” said Michael Mei, managing director of Menlo. “I look forward to many new insights into the depths of the cosmos.”