First light captured by the 4MOST telescope: observation begins of 77,000 stars in an international project led by the UPC
The region of the sky around the Sculptor Galaxy (NGC 253) and the globular cluster NGC 288, targets of the first 4MOST observations. Credit: AIP/Background: Harshwardhan Pathak/Telescope Live
The Visible and Infrared Survey Telescope for Astronomy (VISTA) is located at the Paranal Observatory in Chile’s Atacama Desert, one of the best astronomical sites in the world. Credit: ESO/B. Tafreshi (twanight.org)
The 4MOST telescope at the European Southern Observatory in Chile captured its first light on 18 October, marking the start of new scientific programmes around the world. An international research team led by Alberto Rebassa, a researcher at the UPC and member of the IEEC, and Odette Toloza from the USM in Chile, will observe and analyse the spectra of 77,000 binary stars to shed light on how the Milky Way formed and evolved.
Oct 29, 2025
A binary star is a stellar system composed of two stars bound by gravity, orbiting around each other. One type of binary system involves a Sun-like star and a white dwarf, the most common type of stellar remnant, formed in the final stage of a star’s life.
Currently, only a few thousand spectra of such binary systems are available, yet they provide highly valuable scientific data. Studying these systems can help uncover key questions such as the relationship between the age and metallicity of our galaxy—essential to understanding how the Milky Way formed and how it has evolved chemically over time—the evolution of compact binary stars and the physical and magnetic properties of Sun-like stars.
This is the main goal of the project led by Alberto Rebassa, a member of the UPC’s Astronomy and Astrophysics Group, a professor at the Castelldefels School of Telecommunications and Aerospace Engineering (EETAC) and a researcher at the Institute of Space Studies of Catalonia (IEEC), together with researcher Odette Toloza of the Federico Santa María Technical University (USM) in Chile.
Also taking part from the UPC are Santiago Torres, Ramón y Cajal researchers Roberto Raddi and María Eugenia Camisassa, and doctoral students Enrique Miguel García Zamora and Aina Ferrer i Burjachs. The team also includes about 30 researchers from 18 institutions and universities in the United Kingdom, Germany, Chile, China, Italy and the United States.
According to Alberto Rebassa, “It is incredibly exciting to see 4MOST reach first light. The scientific community has invested years of hard work to get here, and it is deeply rewarding to see it all come together. The range of science 4MOST will enable is truly impressive, and I’m confident that the data will drive a real revolution in astronomy. I can’t wait to start collecting spectra and discovering what lies ahead.”
First light from the 4MOST telescope
The first light obtained on 18 October by the 4-metre Multi-Object Spectroscopic Telescope (4MOST) marks the start of its scientific journey. The instrument is installed on the VISTA telescope (Visible and Infrared Survey Telescope for Astronomy) at the European Southern Observatory, located in Cerro Paranal, Chile. In this initial observation, 4MOST analysed the light of various cosmic objects, with the Sculptor Galaxy and the globular cluster NGC 288 among the highlights. The telescope captured a spectrum for each observed object, enabling researchers to study their chemical composition, temperature and other properties.
The 4MOST telescope is the largest multi-object spectroscopic facility in the Southern Hemisphere, unique for its combination of a wide field of view, a high number of simultaneous observations and an extensive range of recorded spectral colours. It can analyse the light of 2,400 celestial objects at once, splitting it into 18,000 colour components. To achieve this, 4MOST uses 2,438 optical fibres, each as thin as a human hair. Light from each fibre is transmitted to spectrographs, which separate it into different colours. Its large camera lens system, nearly one metre in diameter, provides a 2.5-degree field of view, five times the apparent size of the Moon and one of the largest in the world for a telescope of this kind.
Research carried out with 4MOST covers a wide range of topics: the origin of chemical elements and the formation of the first stars; the growth of the Milky Way over cosmic time; the formation and evolution of galaxies and black holes; the composition of dark matter that appears to make up most of the mass of galaxies; and the nature of dark energy driving the accelerated expansion of the Universe. By analysing the detailed light spectra of thousands of objects every 10 to 20 minutes, 4MOST will build a vast catalogue of temperatures, chemical compositions, velocities and other physical parameters for tens of millions of objects across the southern sky.
The 4MOST facilities have been designed, built and are operated by a consortium of 30 universities and research institutes in Europe and Australia, coordinated by the Leibniz Institute for Astrophysics Potsdam (AIP). Development began in 2010, and the telescope is expected to operate for at least 15 years. During its first five years, 4MOST will conduct 25 international science programmes, including the project led by Professor Alberto Rebassa.
