Astronomers have unveiled a striking new view of the center of the Milky Way, exposing an intricate network of cosmic gas filaments in unprecedented detail. The image was produced using the Atacama Large Millimeter/submillimeter Array (ALMA) and forms the largest ALMA dataset ever assembled. This massive map will help scientists investigate how stars form and evolve in the most extreme region of our galaxy, near its supermassive black hole.
“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 and a member of the research team. The observations provide a rare look at cold gas, the basic ingredient from which stars are created, across the region known as the Central Molecular Zone (CMZ). For the first time, the cold gas throughout this entire area has been mapped with such precision.
Mapping the Central Molecular Zone
The region captured in the image stretches more than 650 light-years across. It contains dense clouds of gas and dust that surround the supermassive black hole at the center of the Milky Way. “It is the only galactic nucleus close enough to Earth for us to study in such fine detail,” Barnes explains. The new dataset reveals structures throughout the CMZ at many scales, from massive gas formations spanning dozens of light-years to small clouds surrounding individual stars.
The survey responsible for this work is called ACES, short for the ALMA CMZ Exploration Survey. ACES focuses specifically on cold molecular gas, the material that fuels star formation. By analyzing the signals from this gas, researchers uncovered a surprisingly complex chemical environment. The survey detected dozens of molecules, including relatively simple ones such as silicon monoxide as well as more complex organic compounds like methanol, acetone or ethanol.
Extreme Star Formation Near the Galactic Center
In the CMZ, cold molecular gas moves along elongated filaments that funnel material into dense clumps where stars can form. Astronomers understand this process fairly well in quieter parts of the Milky Way, but conditions near the galactic center are far more intense.
“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. Through the ACES survey, researchers hope to learn how such violent environments influence the birth of stars and whether current theories of star formation remain valid under these extreme conditions.
“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.”
Building the Largest ALMA Mosaic
To gather this enormous dataset, astronomers used ALMA, a powerful observatory operated by ESO and its partners in Chile’s Atacama Desert. This marks the first time such a large portion of the galactic center has been surveyed with ALMA, resulting in the observatory’s largest image so far. The final mosaic was created by combining many individual observations, much like assembling pieces of a puzzle. On the sky, the completed image spans a length equivalent to three full Moons placed 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 involved in the project. Results from the ACES program are described in five papers accepted for publication in Monthly Notices of the Royal Astronomical Society, with a sixth currently undergoing final review.
Future Observations Will Reveal Even More
“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.”
Research Papers and Data Availability
This work is presented in a series of papers describing the ACES data, which will appear in Monthly Notices of the Royal Astronomical Society:
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)
The full dataset will be available through the ALMA Science Portal at https://almascience.org/alma-data/lp/aces.
Global Collaboration Behind the ACES Project
The ACES collaboration includes more than 160 scientists ranging from Master’s students to retired researchers, representing over 70 institutions across Europe, North and South America, Asia, and Australia. The project was initiated and led by Principal Investigator Steven Longmore (Liverpool John Moores University, UK), along 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. Contributors include 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), along with more than 30 additional researchers who assisted with data reduction.