A new telescope called 4MOST has begun operations at the European Southern Observatory’s VISTA telescope in Chile, marking a significant step for astronomical research. The instrument achieved its first light on October 18, 2025, beginning its scientific mission to study the southern sky.
Unlike conventional telescopes that take images, 4MOST uses more than 2,400 optical fibres to collect spectra from thousands of stars and galaxies at once. This approach allows astronomers to analyze temperature, motion, and chemical composition of celestial objects by splitting their light into 18,000 color components.
“This is an outstanding feat made possible by an amazing development team,” said Dr Roelof de Jong, Principal Investigator of 4MOST at the Leibniz Institute for Astrophysics Potsdam (AIP). “The first data already look fantastic. To catch light that’s travelled for billions of years in a fibre the size of a hair is mind-boggling.”
The telescope’s first observations focused on two regions: the Sculptor Galaxy and Globular Cluster NGC 288. These initial results showed 4MOST’s ability to capture data from diverse objects simultaneously.
“With first light, we’re opening a new chapter in sky surveys,” said Professor Matthias Steinmetz, Scientific Director at AIP. “4MOST will help to answer fundamental questions about the formation of the Milky Way, the evolution of galaxies and the forces that shape the Universe.”
The project involves collaboration among 30 universities and research institutes across Europe and Australia, including the University of Cambridge. More than 700 scientists are working on 25 science programs with 4MOST.
Engineers have outfitted VISTA with a new optical camera nearly one metre wide, giving 4MOST a large field of view among telescopes of its type. The fibres can be repositioned within minutes to target new areas of the sky, with high precision.
Light from each fibre is sent to three spectrographs, which break it into red, green, and blue components before further analysis with detectors totaling 36 megapixels. Two spectrographs cover visible and infrared light; a third focuses on specific bands to study stellar chemistry.
Nightly observation planning will be coordinated by Germany’s Max Planck Institute for Extraterrestrial Physics, while operations are managed by the European Southern Observatory in Chile.
Data collected by 4MOST will be transferred to the University of Cambridge’s Institute of Astronomy for processing. The team there will extract physical information from raw spectra before passing it to AIP and ESO for distribution to astronomers worldwide.
“The 4MOST instrument, with its huge number of optical fibres, has meant the development of a highly sophisticated, high throughput, data flow system, running in Cambridge,” said Dr Nicholas Walton, who leads data management for 4MOST. “Our advanced pipeline delivers the highest quality science data, underpinning the amazing discoveries that 4MOST will enable.”
“This is such an exciting time to be an astronomer, as 4MOST and other next-generation telescopes come online,” said Dr Lisa Kelsey from Cambridge’s Institute of Astronomy. “It’s taken a long time and a huge team to get here, but we can’t wait to get to work on some exciting new science.”
Kelsey and colleagues are involved in the Time Domain Extragalactic Survey (TiDES), one of the first major projects using 4MOST. TiDES aims to study brief cosmic events such as supernovae and gamma-ray bursts in distant galaxies. By observing these transients as they occur, researchers hope to learn more about how stars end their lives and how black holes behave.
Over its planned fifteen-year mission, 4MOST is expected to conduct one of the largest spectroscopic surveys ever attempted, providing data that could reshape understanding of astrophysical phenomena.