Lead: An international team has produced the most complete, high-resolution map of cold molecular gas at the center of the Milky Way, using ALMA after a four-year campaign. The map focuses on the Central Molecular Zone (CMZ), the dense, turbulent region around the supermassive black hole Sagittarius A* roughly 4 million times the mass of the Sun. The survey — called ACES — images the raw material for future stars and planets and offers a new dataset for testing theories about how star formation proceeds in extreme environments. Researchers say the data may also shed light on conditions similar to those that existed when our solar system formed.
Key takeaways
- The ACES effort ran for four years and combined observations from the Atacama Large Millimeter/submillimeter Array (ALMA), a network of more than 50 radio antennae on a high Chilean plateau.
- The project produced the first contiguous, high-resolution map of cold molecular gas across the Milky Way’s Central Molecular Zone, covering the full galactic center rather than isolated patches.
- Scientists measured more than 70 molecular spectral lines, including simple diatomics and complex organics such as methanol and ethanol, which can trace physical conditions and chemistry.
- The survey team numbered about 160 people from multiple countries, requiring extensive data stitching and calibration to combine many individual ALMA pointings.
- Maps encode velocity information via spectroscopy and Doppler shifts, revealing gas motions toward and away from Earth and enabling a three-dimensional view of structure and flow.
- Regions with emission from molecules like silicon monoxide likely mark energetic collisions; other color-coded zones indicate quieter, denser reservoirs where collapse may begin.
- Sagittarius A* sits at the dynamic center and exerts strong gravity that influences gas flows, making the CMZ far hotter, denser and more turbulent than the Solar neighborhood.
Background
The Central Molecular Zone is a compact region within the inner few hundred parsecs of the Milky Way that contains a disproportionate amount of the galaxy’s dense gas. Compared with the spiral arms where the Sun resides, the CMZ has higher temperatures, elevated turbulence and stronger tidal forces because of the proximity to the central black hole, Sagittarius A*. These conditions alter how gas fragments, cools and ultimately forms stars, so the CMZ serves as a local laboratory for extreme star formation.
Historically, observations of the galactic center came as focused, high-detail studies on limited targets or as lower-resolution surveys covering wider areas. That trade-off left a gap: no dataset combined uniform high spatial resolution with broad contiguous coverage. The ACES survey was designed to fill that gap by mapping wide areas at ALMA-quality resolution and recording many spectral lines to trace chemistry and motion simultaneously. The result is a coherent picture that lets astronomers compare structures across scales rather than inferring connections from scattered snapshots.
Main event
Over four years, the ACES collaboration used ALMA’s more than 50 antennas on the Chajnantor Plateau to observe a swath of the galactic center repeatedly and at multiple frequencies. The campaign targeted emission from cold molecular gas—the direct precursor to star and planet formation—collecting spectra that encode both composition and velocity. Combining these pointings required careful calibration and image reconstruction to preserve consistent resolution across the mapped area.
Team lead Steven Longmore of Liverpool John Moores University described the final product as the first integrated map of cold gas in the galactic center: a top-down, contiguous view rather than isolated snapshots. The assembled images use false color to highlight different molecular tracers and velocity channels; those colors do not represent visible light but are assigned after analysis so researchers can distinguish physical and chemical regimes in the CMZ.
The dataset includes signatures from more than 70 molecular spectral lines, spanning simple molecules and more complex organics. Certain line emitters, such as silicon monoxide, appear in regions where energetic shocks and cloud collisions are suspected, while other tracers flag colder, more quiescent pockets that are more likely to collapse into stars. By measuring Doppler shifts in each spectral line, astronomers can map how gas streams toward or away from Sagittarius A*, revealing flow patterns influenced by the central mass and by galactic dynamics.
Analysis & implications
The ACES map advances the study of star formation under extreme conditions by providing a uniform dataset that constrains how turbulence, temperature and tidal shear affect fragmentation. Models that predict when and where dense cores form can now be tested against a continuous observational baseline across the CMZ, rather than against disjointed case studies. This helps refine theoretical thresholds for collapse and may require adjustments to prescriptions used in galaxy-scale simulations.
Because the CMZ’s physical state resembles environments common in young, rapidly evolving galaxies billions of years ago, the survey offers an observational bridge between local star formation and the early universe. If chemistry and collapse pathways in the CMZ match those inferred for high-redshift galaxies, ACES can inform hypotheses about how the first generations of stars and planetary systems assembled in the cosmos.
The detection of complex organic molecules, some regarded as possible precursors to amino acids, is noteworthy but does not by itself demonstrate a direct path to life-bearing chemistry. Instead, it shows that rich organic chemistry can persist or arise even in turbulent, dense environments. Future targeted studies of specific cores within the CMZ will be needed to evaluate whether those molecules survive into protostellar disks or are processed further by shocks and radiation.
Comparison & data
| Survey | Area strategy | Resolution | Spectral lines | Duration |
|---|---|---|---|---|
| Prior wide surveys | Large area, low resolution | Low | Few | Varied |
| Targeted ALMA studies | Small patches, high resolution | High | Multiple | Short campaigns |
| ACES (this work) | Contiguous, wide and high-resolution | High | >70 | 4 years |
The table summarizes how ACES differs from previous efforts: it combines contiguous areal coverage with ALMA-level spatial fidelity and a broad spectral inventory. That combination allows cross-scale comparisons and uniform statistical studies of cloud properties across the CMZ. The consistent resolution and spectral sampling reduce systematic biases that arise when stitching together heterogeneous datasets.
Reactions & quotes
We had detailed studies of small regions before, but never a single, continuous map of the cold gas across the entire galactic center.
Steven Longmore, Liverpool John Moores University (project lead)
Longmore framed the result as a new vantage point that turns isolated observations into a comprehensive map. He emphasized the logistical and technical work required to assemble many ALMA pointings into a consistent mosaic.
This kind of work shows how modern astronomy increasingly depends on large international teams and complex instrument operations.
Richard Teague, MIT (planetary science professor, external commentator)
Teague highlighted the collaborative scale—engineers, operators in Chile and a global science team—and noted that the survey strikes a balance between area and detail that previous efforts lacked.
Unconfirmed
- Whether specific complex molecules detected in the CMZ will survive intact into protostellar disks and become incorporated into forming planets remains unproven; follow-up observations are required.
- The interpretation that certain color-coded regions definitively indicate cloud collisions relies on models linking silicon monoxide emission to shocks; alternative explanations are possible and need targeted confirmation.
- Claims that the CMZ is a perfect analog for early-universe galaxies are approximate; while similar in some physical parameters, differences in metallicity, radiation fields and galactic environment may limit one-to-one comparisons.
Bottom line
The ACES map is a step change in how astronomers observe the Milky Way’s center: for the first time, cold, star-forming gas has been imaged across the entire CMZ at consistently high resolution with a rich spectral inventory. That combination allows robust comparisons of cloud properties, dynamics and chemistry across a region shaped by extreme gravity and turbulence. The dataset will serve as a benchmark for theory and a reference for targeted follow-up studies aimed at the earliest phases of star and planet formation.
Looking ahead, researchers plan deeper, higher-sensitivity integrations, focused studies of candidate pre-stellar cores and complementary observations at other wavelengths to trace protostellar disks and ionized gas. Together, those steps will test whether the gas structures and chemistries mapped by ACES can explain how stars and planetary systems emerge in environments both near and far.
Sources
- CNN (news report summarizing the ACES release)
- ALMA (official observatory information and instrumentation overview)
- Liverpool John Moores University (academic institution; project lead affiliation and releases)
- Massachusetts Institute of Technology (MIT) (academic commentary from external researcher)