Largest image shows cosmic gas at the heart of the Milky Way

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Astronomers have captured the central region of our galaxy, the 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.

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.)

“It’s a place of extremes, invisible to our eyes, but now revealed in extraordinary detail,” said 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, stated ESO

Different molecules in the centre of the Milky Way observed with ALMA. This montage shows the distribution of different molecules in the Central Molecular Zone (CMZ) of the Milky Way. The observations were made with the Atacama Large Millimeter/submillimeter Array (ALMA), as part of the ALMA CMZ Exploration Survey or ACES. ACES has mapped the distribution of several dozen molecules at the centre of our galaxy. Here we show five of them, from top to bottom: carbon monosulphide, isocyanic acid, silicon monoxide, sulphur monoxide, and cyanoacetylene. Image credit: ALMA(ESO/NAOJ/NRAO)/S. Longmore et al.

The region captured 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,” Barnes said. 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.

Location of the Central Molecular Zone in the Milky Way. This image shows the location of the Central Molecular Zone (CMZ), a region at the core of our galaxy rich in dense and intricate gas clouds. This zone has been mapped with the Atacama Large Millimeter/submillimeter Array (ALMA), as part of the ALMA CMZ Exploration Survey or ACES. The inset is an ACES image where different molecules are displayed in different colours. The entire image – the largest ever made with ALMA – is as long as three full Moons side-by-side in the sky. Image credit: ALMA(ESO/NAOJ/NRAO)/S. Longmore et al. Stars in inset: ESO/D. Minniti et al. Milky Way: ESO/S. Guisard

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.

This video explores the molecular gas in the centre of the Milky Way in unprecedented detail. This new image, obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), shows the distribution of different molecules, each displayed in a different colour. This map will allow astronomers to understand how stars form in the extreme and chaotic environment in the centre of our galaxy. Credit: ALMA(ESO/NAOJ/NRAO)/S. Longmore et al. Background: ESO/D. Minniti et al. Music: Mylonite – Champ magnétique (Intro), Mylonite – Breath of my soul Script: J. C. Muñoz. Editing: M. Martins

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,” said 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.

Zooming into the gas at the core of the Milky Way
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The video zooms into the complex molecular gas in the centre of the Milky Way – a chaotic and extreme environment where stars don’t necessarily form in the same way as they do in the outskirts of our galaxy. The video combines images taken with different telescopes at different times and various wavelengths. The clip begins with a wide view of the night sky in visible light, and ends with an image taken at millimetre wavelengths with the Atacama Large Millimeter/submillimeter Array (ALMA). Different molecules are shown with different colours. Credit: ESO/L. Calçada/N. Risinger (skysurvey.org)/Digitized Sky Survey 2/ALMA (ESO/NAOJ/NRAO)/S. Longmore et al. Music: Azul Cobalto.

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

This video shows footage of Steve Longmore (Liverpool John Moores University) talking about ACES and the latest data release. Credit: Steve Longmore

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.

Katharina Immer, an astronomer at the European Southern Observatory, on the ACES research. Credit: ESO

“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," said Katharina Immer, an ALMA astronomer at ESO who is also part of the project. The data provided by 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.

Ashley Barnes, an astronomer at the European Southern Observatory, on the ACES research, talks about the findings. ACES, which stands for ALMA CMZ Exploration Survey, is a large observation programme with the Atacama Large Millimeter/submillimeter Array (ALMA) focusing on the very central region (the CMZ or central molecular zone) of our galaxy, the Milky Way. Credit: ESO

“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,” Barnes said. “In many ways, this is just the beginning.”

The papers
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Paper I - ALMA Central Molecular Zone Exploration Survey (ACES) I: Overview paper
Paper II - ALMA Central Molecular Zone Exploration Survey (ACES) II: 3mm continuum images
Paper III - ALMA Central Molecular Zone Exploration Survey (ACES) III: Molecular line data reduction and HNCO & HCO+ data
Paper IV - ALMA Central Molecular Zone Exploration Survey (ACES) IV: Data of the two intermediate-width spectral windows
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).

You will reach the data itself -when it will be available- from the ALMA Science Portal.

Teams
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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.

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