Press Release

Largest image of its kind shows hidden chemistry at the heart of the Milky Way

25 February 2026

Largest ALMA image ever shows the molecular gas in the centre of the Milky Way (Credit: ALMA(ESO/NAOJ/NRAO)/S. Longmore et al. Background: ESO/D. Minniti et al.)

Astronomers have captured the central region of our Milky Way in a striking new image, unveiling a complex network of filaments of cosmic gas in unprecedented detail. Obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), this rich dataset — the largest ALMA image to date — will allow astronomers to probe the lives of stars in the most extreme region of our galaxy, next to the supermassive black hole at its centre.

“It’s a place of extremes, invisible to our eyes, but now revealed in extraordinary detail,” says Ashley Barnes, an astronomer at the European Southern Observatory (ESO) in Germany who is part of the team that obtained the new data. The observations provide a unique view of the cold gas — the raw material from which stars form — within the so-called Central Molecular Zone (CMZ) of our galaxy. It is the first time the cold gas across this whole region has been explored in such detail.

The region featured in the new image spans more than 650 light-years. It harbours dense clouds of gas and dust, surrounding the supermassive black hole at the centre of our galaxy. “It is the only galactic nucleus close enough to Earth for us to study in such fine detail,” says Barnes. The dataset reveals the CMZ like never before, from gas structures dozens of light-years across all the way down to small gas clouds around individual stars.

The gas that ACES — the ALMA CMZ Exploration Survey — specifically explores is cold molecular gas. The survey unpacks the intricate chemistry of the CMZ, detecting dozens of different molecules, from simple ones such as silicon monoxide to more complex organic ones like methanol, acetone or ethanol.

Cold molecular gas flows along filaments feeding into clumps of matter out of which stars can grow. In the outskirts of the Milky Way we know how this process happens, but within the central region the events are much more extreme. “The CMZ hosts some of the most massive stars known in our galaxy, many of which live fast and die young, ending their lives in powerful supernova explosions, and even hypernovae,” says ACES leader Steve Longmore, a professor of astrophysics at Liverpool John Moores University, UK. With ACES, astronomers hope to better understand how these phenomena influence the birth of stars and whether our theories of star formation hold in extreme environments.

“By studying how stars are born in the CMZ, we can also gain a clearer picture of how galaxies grew and evolved,” Longmore adds. “We believe the region shares many features with galaxies in the early Universe, where stars were forming in chaotic, extreme environments.”

To collect this new dataset, astronomers used ALMA, which is operated by ESO and partners in Chile’s Atacama Desert. In fact, this is the first time such a large area has been scanned with this facility, making this the largest ALMA image ever. Seen in the sky, the mosaic — obtained by stitching together many individual observations like putting puzzle pieces together — is as long as three full Moons side-by-side.

“We anticipated a high level of detail when designing the survey, but we were genuinely surprised by the complexity and richness revealed in the final mosaic," says Katharina Immer, an ALMA astronomer at ESO who is also part of the project. The data from ACES are presented in five papers accepted for publication in Monthly Notices of the Royal Astronomical Society, with a sixth in the final review stages.

“The upcoming ALMA Wideband Sensitivity Upgrade, along with ESO’s Extremely Large Telescope, will soon allow us to push even deeper into this region — resolving finer structures, tracing more complex chemistry, and exploring the interplay between stars, gas and black holes with unprecedented clarity,” says Barnes. “In many ways, this is just the beginning.”

More information

This research was presented in a series of papers presenting the ACES data, to appear in Monthly Notices of the Royal Astronomical Society:

• Paper I - ALMA Central Molecular Zone Exploration Survey (ACES) I: Overview paper https://arxiv.org/abs/2602.20340 
• Paper II - ALMA Central Molecular Zone Exploration Survey (ACES) II: 3mm continuum images https://arxiv.org/abs/2602.20240 
• Paper III - ALMA Central Molecular Zone Exploration Survey (ACES) III: Molecular line data reduction and HNCO & HCO+ data https://arxiv.org/abs/2602.20276 
• Paper IV - ALMA Central Molecular Zone Exploration Survey (ACES) IV: Data of the two intermediate-width spectral windows https://arxiv.org/abs/2602.20445 
• Paper V - ALMA Central Molecular Zone Exploration Survey (ACES) V: CS(2-1), SO 2_3-1_2, CH3CHO 5_(1,4)-4_(1,3), HC3N(11-10) and H40A lines data
• Paper VI - ALMA Central Molecular Zone Exploration Survey (ACES) VI: ALMA Large Program Reveals a Highly Filamentary Central Molecular Zone (undergoing minor revision) https://arxiv.org/abs/2602.20262 

The data itself will be available from the ALMA Science Portal at https://almascience.org/alma-data/lp/aces. 

The international ACES team is composed of over 160 scientists ranging from Master’s students to retirees, working at more than 70 institutions across Europe, North and South America, Asia, and Australia. The project was instigated and led by Principal Investigator Steven Longmore (Liverpool John Moores University, UK), together with co-PIs Ashley Barnes (European Southern Observatory, Germany), Cara Battersby (University of Connecticut, USA [Connecticut]), John Bally (University of Colorado Boulder, USA), Laura Colzi (Centro de Astrobiología, Madrid, Spain [CdA]), Adam Ginsburg (University of Florida, USA [Florida]), Jonathan Henshaw (Max Planck Institute for Astronomy, Heidelberg, Germany), Paul Ho (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan), Izaskun Jiménez-Serra (CdA), J. M. Diederik Kruijssen (COOL Research DAO), Elisabeth Mills (University of Kansas, USA), Maya Petkova (Chalmers University of Technology, Sweden), Mattia Sormani (Dipartimento di Scienza e Alta Tecnologia (DiSAT), University of Insubria, Italy), Robin Tress (École Polytechnique Fédérale de Lausanne, Switzerland & Institut für Theoretische Astrophysik, Universität Heidelberg, Germany), Daniel Walker (UK ALMA Regional Centre Node, University of Manchester, UK), and Jennifer Wallace (Connecticut).

Within ACES, the ALMA data reduction working group is coordinated by Adam Ginsburg, Daniel Walker, and Ashley Barnes, and includes Nazar Budaiev (Florida), Laura Colzi (CdA), Savannah Gramze (Florida), Pei-Ying Hsieh (National Astronomical Observatory of Japan, Mitaka, Tokyo, Japan), Desmond Jeff (Florida), Xing Lu (Shanghai Astronomical Observatory, Chinese Academy of Sciences, China), Jaime Pineda (Max-Planck-Institut für extraterrestrische Physik, Germany), Marc Pound (University of Maryland, USA), and Álvaro Sánchez-Monge (Institut de Ciències de l’Espai, CSIC, Bellaterra, Spain; Institut d’Estudis Espacials de Catalunya, Castelldefels, Spain), together with more than 30 additional team members who contributed to the data reduction effort.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA. 

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration for astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, Czechia, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal, ESO will host and operate the south array of the Cherenkov Telescope Array Observatory, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates ALMA on Chajnantor, a facility that observes the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society. 

Links

• ACES overview paper
• ACES science data in the ALMA Science Portal
• Photos of ALMA  
• ALMA Wideband Sensitivity Upgrade
• Find out more about ESO's Extremely Large Telescope on our dedicated website and press kit
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Contacts

Ashley Thomas Barnes
Astronomical Data Scientist, European Southern Observatory (ESO)
Garching bei München, Germany
Tel: +49 89 3200 6729
Email: Ashley.Barnes@eso.org

Steven Longmore
Professor of Astrophysics, Astrophysics Research Institute, Liverpool John Moores University
Liverpool, UK
Tel: +44 (0)151 231 2929
Email: S.N.Longmore@ljmu.ac.uk

Katharina Immer
ALMA Regional Centre Astronomer, European Southern Observatory (ESO)
Garching bei München, Germany
Tel: +49 89 3200 6471
Email: Katharina.Immer@eso.org

Adam Ginsburg
Associate Professor, Department of Astronomy, University of Florida
Gainesville, FL, USA
Tel: +1 352-294-1879
Email: adamginsburg@ufl.edu, adam.g.ginsburg@gmail.com

Daniel Walker
Astronomer, UK ALMA Regional Centre Node, University of Manchester
Manchester, UK
Email: daniel.walker-2@manchester.ac.uk

Pei-Ying Hsieh
Assistant Professor, National Astronomical Observatory of Japan, Tokyo, Japan
Email: pei-ying.hsieh@nao.ac.jp

Xing Lu
Professor, Shanghai Astronomical Observatory, Chinese Academy of Sciences
Shanghai, China
Email: xinglu@shao.ac.cn, xinglv.nju@gmail.com

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: press@eso.org

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