Thousands of eyes on the sky: 4MOST sees first light

A new astronomical instrument will observe more than 25 million different cosmic objects over the next five years. This 4-metre Multi-Object Spectroscopic Telescope (4MOST) has just completed its first test observations. The instrument is intended to unravel our galactic history, investigate dark matter and study the origin of stars. 4MOST is installed on the Visible and Infrared Survey Telescope for Astronomy (VISTA) in Chile. Dutch researchers, including those from the University of Groningen, play an important role in the project.

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Whereas many telescope instruments observe objects one by one, 4MOST is designed to capture the light from thousands of sources simultaneously. It does this using more than 2,400 thin optical fibres, each as thick as a human hair. The light is guided through these glass fibres to three separate spectrographs, which split it into up to 18,000 colour components. In this way, the device measures an extensive spectrum from each source, most of which lies within the visible light. This enables astronomers to determine the properties of cosmic sources, such as their chemical composition, speed, and distance from Earth.

The first observations with 4MOST were made last weekend. During the test, 4MOST collected spectra from stars in our Milky Way and from more than a thousand other galaxies. The number of objects it can observe simultaneously, its large field of view, and the large number of spectral colours it can record at the same time make the instrument unique. With a single observation, 4MOST can serve ten or more scientific studies simultaneously.

Research on the Milky Way

Astronomers at the University of Groningen are using the 4MOST observations to obtain the most complete dynamic three-dimensional model of our Milky Way possible. To this end, they are combining data with previous observations from the Gaia satellite, which collected information on nearly two billion stars between 2013 and 2025.

Else Starkenburg is an associate professor at the Kapteyn Institute of the University of Groningen and, together with her colleagues, focuses on stars in the outer regions of the Milky Way. These are very old stars. Observations of them by 4MOST will hopefully answer questions about the early days of the Milky Way, but also about the early structure of the universe in general. ‘For me, it is a fantastic prospect to be able to study the Milky Way in such detail. In addition to data on the movement of stars, 4MOST also provides information about the elements in their atmospheres. This allows us to accurately determine the history of our galaxy,’ says Starkenburg.

University of Groningen professor Amina Helmi was one of the founders of 4MOST. ‘It became clear to me and a number of colleagues early on that information about the chemical composition of stars is important for unravelling the history of the Milky Way. That is what 4MOST will provide in large numbers. I have been looking forward to this for a very long time.’