A thousand eyes on the Universe: new UK-led astronomy instrument takes first look into the heart of the Milky Way

The Multi-Object Optical and Near-infrared Spectrograph (MOONS) has achieved First Light at the European Southern Observatory's (ESO) Very Large Telescope (VLT) at the Paranal Observatory in Chile.

This milestone marks the beginning of a new era in cosmic exploration, as MOONS prepares to survey millions of stars and galaxies and reveal how the Universe evolved over billions of years, from its perch high in the Chilean mountains.

In astronomy, First Light marks the moment a new telescope or instrument successfully observes an astronomical target in the sky for the first time. This milestone for MOONS represents the culmination of more than a decade of international collaboration involving engineering and science partners across the UK, Italy, France, Portugal, Switzerland, Chile and ESO.

For its first observation, MOONS captured the heart of the Milky Way in a new way: Being sensitive to near-infrared wavelengths, MOONS can peer through the dust that obscures our view toward the central regions of our Galaxy and beyond, providing an unprecedented spectroscopic view of this densely populated region.

MOONS combines two unique capabilities: the ability to observe nearly 1,000 stars or galaxies simultaneously, while working over a wide range of wavelengths covering the visible and near-infrared light. These capabilities are enhanced by the 8-metre aperture of the ESO VLT, making it one of the most powerful spectroscopic facilities ever constructed.

The instrument was built by an international consortium led by the UK Astronomy Technology Centre (UK ATC) in Edinburgh, part of the UK’s Science and Technology Facilities Council (STFC), and includes researchers from the University of Cambridge. 

“MOONS is an extraordinary new tool in our astronomers’ toolbox,” said co-UK Principal Investigator Professor Roberto Maiolino, from Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology. “The ability to study 1000 objects simultaneously in the infrared is a whole new way for us to study how our universe, and the structures within it, formed and evolved over billions of years.”

“For years our scientists, engineers and technicians have worked together to overcome remarkable technological challenges and create an instrument of exceptional capability,” said Dr Oscar Gonzalez, MOONS co-UK Principal Investigator and Head of Project Science and Strategy at UK ATC. “For me, First Light is a celebration of their expertise, dedication and perseverance. It marks the exact moment in which years of work are transformed into discovery.”

MOONS is a spectrograph, so it doesn’t take pictures; instead, it splits the light from stars and galaxies into detailed spectra. By analysing these spectra, astronomers can determine properties such as an object's chemical composition, temperature, motion and distance. One observation can collect this information for nearly 1,000 objects simultaneously. This is the first time this amount of data has been captured in a single observation.

By collecting and analysing light from millions of objects over its lifetime, astronomers will address some of astronomy's biggest questions, from uncovering how the Milky Way formed and evolved to tracing the growth of galaxies across billions of years of cosmic history.

The new instrument operates at cryogenic temperatures, with its optics and mechanism cooled to around 130 Kelvin (-140°C) and its detectors operating at approximately 40 Kelvin (-230°C), to reach the stability and sensitivity needed to detect the faintest light from distant galaxies and stars. 

To achieve this, MOONS uses a giant cryostat believed to be the largest ever built for a ground-based astronomical telescope. In addition, its robotic fibre positioning system places 1,000 optical fibres onto their celestial targets with micrometre accuracy, allowing astronomers to survey the sky on a scale and efficiency never before possible.

Professor Michele Dougherty, STFC Executive Chair and UK Astronomer Royal, travelled to Chile to join the UK ATC team to witness First Light. She said: “Seeing MOONS achieve First Light was tremendously exciting. A landmark moment, not only for the international team behind this remarkable instrument, but for astronomy as a whole. It demonstrates the transformational science that innovative instrumentation can deliver.

“MOONS is also a powerful example of the UK's world-leading expertise in astronomical technology and of STFC's commitment to ground-based astronomy. Through investment in cutting-edge facilities and by enabling ambitious international collaborations, we are ensuring that UK scientists and engineers remain at the forefront of discovery, helping to answer some of the biggest questions about our Universe.”

“MOONS opens a new window onto the Universe, allowing us to explore the physical, chemical, dynamical and environmental properties of millions of stars and galaxies across more than 13 billion years of cosmic history,” said Michele Cirasuolo, MOONS Principal Investigator and ESO Instrumentation Programme Manager. “It will take us to new frontiers in our understanding of how the Milky Way and galaxies have formed and evolved with time. I am incredibly proud of the team and hugely excited to see what new discoveries and new horizons in our understanding of the Universe lie ahead.”

MOONS is expected to become a cornerstone instrument for the VLT, delivering vast spectroscopic datasets that will complement observations from facilities including ESA’s Gaia mission, the Vera C Rubin Observatory and future space missions.

With First Light now achieved, the MOONS team will continue commissioning and calibration activities before beginning full scientific operations. These initial observations already demonstrate the potential of this next-generation instrument and mark the beginning of a new chapter in astronomical exploration.

Adapted from an ATC media release.