Stockholm university
Department of Astronomy

First light with 4MOST

On October 18 2025, the 4-metre Multi-Object Spectroscopic Telescope (4MOST) facility, installed on the VISTA telescope at the European Southern Observatory’s (ESO) Paranal Observatory in Chile, obtained its first light. This milestone is a crucial step in the lifecycle of a telescope and marks the moment in time when it is ready to begin its scientific journey.

4MOST multi object spectroscopy setup
The hexagonal 4MOST field-of-view and the many objects (marked with different coloured dots for different types of objects). 4MOST collected a spectrum for each of these individual objects, allowing us to study their properties such as chemical composition or temperature. Credit: AIP/Background: Harshwardhan Pathak/Telescope Live

However, images of the sky is not what this telescope takes – instead it measures spectra, which means that it can divide up the light from each object in colour components. Because of this the telescope can analyze the light from 2400 celestial objects simultaneously, divided up into 18000 colour components. Using this data astronomers can study the detailed chemical composition and physical properties of the objects.

When 4MOST is fully operational it will investigate how stars and planets form, how the Milky way and other galaxies formed, and explore black holes and other exotic objects. By analyzing the spectra from thousands of objects obtained every 10-20 minutes 4MOST will make it possible to create a catalogue of temperatures, chemical compositions, velocities, and many other physical properties for millions of objects all across the southern night sky.

This remarkable moment marks the end of more than a decade of intense preparation and the beginning of as many years of exciting science exploration of many millions of stars in our Galaxy and beyond. " says Karin Lind, Associate Professor at Stockholm University, and former Galactic Project Scientist of 4MOST.

The construction of 4MOST was began in 2010 and is today the largest spectroscopic survey facility on the southern hemisphere. What makes it unique is the combination of its large field of view, the capability to observe many objects simultaneously, and the number of colour components that can be measured. The facility is designed to be operational for at least 15 years.

Sweden has played a crucial role in the 4MOST project from the start with active participation from astronomers at Stockholm, Uppsala, and Lund University.

 
The 4-metre Multi-Object Spectroscopic Telescope (4MOST) has captured its very first spectra! 4MOST simultaneously collected light from 2000 objects, including the Sculptor galaxy, the globular cluster NGC 288, and the active core of a distant galaxy, revealing their detailed chemical signatures. Video Credit: AIP/R. de Jong, AIP/K. Riebe, AIP/A. Saviauk, CRAL/J.-K. Krogager

Learn more about 4MOST in the project press release.  

Research subject
Stars, Planets and Astrobiology
Research group

Last updated: October 22, 2025

Source: Department of Astronomy

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