Research “First Light” for New Astronomical Instrument in Chile
3 November 2025
Spectrograph and software from Heidelberg: Multi-Object Telescope 4MOST has started operations
Capturing the light from 2,400 celestial objects at the same time and taking it apart into 18,000 spectral colors to evaluate the data – that is now possible with a new astronomic instrument at the Paranal Observatory of the European Southern Observatory (ESO) in Chile’s Atacama Desert. Scientists and engineers from Heidelberg University played a major part in designing, engineering and building the 4-metre Multi-Object Spectroscopic Telescope (4MOST) and in developing the control software. 4MOST has now started operations with “first light” – the moment in which a telescope first captures light from a cosmic object. The high-end facility of modern astronomy is intended to enable new insights into the formation and evolution of, for example, the Milky Way and other galaxies.
“4MOST is the biggest instrument for spectroscopic multi-object observations in the southern hemisphere. It is characterized by its unique combination of a large field of view, the abundance of objects that can be observed in parallel and the high number of spectral colors registered simultaneously,” says Prof. Dr Andreas Quirrenbach, Director of the Königstuhl Observatory, which is part of the Centre for Astronomy of Heidelberg University. The spectroscopic instrument was designed and built by a consortium of 30 universities and research institutes in Europe and Australia. The Heidelberg observatory played a leading role. Over 2,400 tiny optical fibers can be positioned in the field of view such that their tips capture the light from celestial objects. Through the optical fibers it is directed into three spectographs and there unraveled into thousands of spectral color components. From this data, astronomers can determine the chemical composition and other properties of the objects observed.
The high-resolution spectrograph – one of the central elements of 4MOST – was designed, engineered and built at the Königstuhl Observatory. Its purpose is for examinations such as chemical tagging. This astrophysical technique uses the composition of a star to trace its origin or identify groups of stars that have probably formed together in the same stellar cluster or the same molecular cloud. “Ultimately, with its assistance, we want to step by step reconstruct the formation and evolution of the Milky Way,” says Prof. Dr Norbert Christlieb, deputy director of the Königstuhl Observatory and principal investigator of one of the 18 scientific 4MOST projects.
As a high-end instrument of modern astronomy the Multi-Object Spectroscopic Telescope calls for an equally demanding software, which coordinates its performance, the operation of the astronomic instrument and data output. It was also developed at the Königstuhl Observatory. This software controls the connected hardware – e.g., cameras, apertures, lamps and motors – and generates the data products that flow into the ESO data archive and the scientific evaluation. Mounted on the VISTA telescope, 4MOST will supply large quantities of data for astrophysical research over many years. Exposures that are typically ten to twenty minutes long will, in a period of five years, give rise to a catalog with information about dozens of millions of objects scattered over the whole southern sky.
The lead partner in the 4MOST consortium is the Leibniz Institute for Astrophysics Potsdam. The Multi-Object Telescope captured the first light from the Universe on 18 October 2025 and became fully operational.