ALMA Creates Its Largest Image Ever, Mapping 650 Light-Years of Hidden Chemistry at the Milky Way's Core
The ACES survey stitched together ALMA's biggest mosaic to date, revealing dozens of molecules and intricate gas filaments across the galaxy's Central Molecular Zone.
Overview
An international team of more than 160 astronomers has used the Atacama Large Millimeter/submillimeter Array (ALMA) to produce the largest image in the observatory’s history, covering over 650 light-years of the Milky Way’s Central Molecular Zone (CMZ). The mosaic, equivalent in angular size to three full Moons placed side by side, reveals a previously hidden network of cold gas filaments and dozens of molecular species in the extreme environment surrounding the galaxy’s supermassive black hole. Six peer-reviewed papers detailing the findings have been accepted by Monthly Notices of the Royal Astronomical Society.
What We Know
The results come from the ALMA CMZ Exploration Survey (ACES), a large collaborative project led by principal investigator Steven Longmore of Liverpool John Moores University, with co-principal investigators Ashley Barnes of ESO and Cara Battersby of the University of Connecticut, along with 13 other co-PIs. The team drew researchers from more than 70 institutions across six continents.
The survey mapped cold molecular gas across the entire CMZ for the first time at this level of detail. The gas flows along elongated filaments that funnel material into dense clumps where new stars can form. Structures in the image range from dozens of light-years across down to small gas clouds surrounding individual stars.
ACES detected dozens of molecular species, from simple compounds like silicon monoxide, sulfur monoxide, and carbon monosulfide to complex organic molecules including methanol, acetone, ethanol, isocyanic acid, and cyanoacetylene. This chemical census provides what the team describes as a roadmap for understanding how stars form under the most extreme conditions found in our galaxy.
“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 Longmore in a statement released by ALMA.
Ashley Barnes of ESO described the region as “a place of extremes, invisible to our eyes, but now revealed in extraordinary detail”.
Why It Matters
The CMZ is the most extreme star-forming environment in the Milky Way, and it shares characteristics with galaxies in the early universe where star formation occurred in similarly chaotic, dense conditions. By studying star formation near a supermassive black hole in our own galaxy, astronomers can develop models applicable to distant galaxies that are too far away to observe at this resolution.
The chemical diversity revealed by ACES is also significant. The presence of complex organic molecules in the vicinity of a supermassive black hole suggests that the building blocks of more complex chemistry can survive and even thrive under intense radiation and gravitational forces.
What Comes Next
The full ACES dataset is now publicly available through the ALMA Science Portal, and the team expects other research groups to mine the data for years to come. Two upcoming facilities will push the observations further: ALMA’s planned Wideband Sensitivity Upgrade will increase the telescope’s spectral bandwidth, enabling detection of fainter molecular lines, while ESO’s Extremely Large Telescope will resolve finer structures and probe how individual stars interact with the surrounding gas and the central black hole.