ALMA Unveils Massive Map of the Milky Way’s Core, Decoding the Chemistry of Star Birth

On February 25, 2026, the European Southern Observatory (ESO) unveiled a record-breaking mosaic image that provides an unprecedented look at the gas fueling star formation in the heart of the Milky Way. Captured by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, this expansive visual covers the Central Molecular Zone (CMZ) across a span of more than 650 light-years. As the largest image ever produced by this instrument, the survey is a cornerstone of the ALMA Survey of the Central Molecular Zone (ACES) program, offering a high-resolution view of the cold molecular gas that serves as the primary building block for new stars.

The intricate map utilizes a sophisticated color-coding system to distinguish between various chemical signatures: sulfur monoxide is represented in cyan, silicon monoxide in green, isocyanic acid in red, cyanoacetylene in blue, and carbon monosulfide in purple. While the actual density of stars in the CMZ is far higher than what appears in this specific visualization, the focus remains on the structural nuances of the molecular clouds. To provide context, foreground stellar data was captured separately using the ESO’s VISTA telescope in the infrared spectrum. This region is of critical importance as it contains nearly 80% of the entire Galaxy’s dense, cold gas and surrounds the supermassive black hole, Sagittarius A* (Sgr A*).

Professor Steve Longmore, the principal investigator for the ACES project, noted that studying star birth in this sector is vital for understanding how galaxies grow, as the conditions within the CMZ mirror those found in the early universe. The findings, along with the release of the comprehensive dataset, are being published in a series of papers in the "Monthly Notices of the Royal Astronomical Society." The project involves a massive collaborative effort, including key figures like co-principal investigator Ashley Barnes from the ESO. The data has already identified dozens of unique molecules, including complex organic compounds such as methanol, acetone, and ethanol, which Dr. Barnes suggests are essential for understanding the origins of planetary ingredients and potentially life itself.

Beyond chemical diversity, the research has highlighted a vast network of elongated, filamentary gas structures that theorists believe act as conduits, funneling matter into the dense clusters where star formation begins. Dr. Daniel Walker confirmed that these widespread filaments, which were previously only seen in isolated pockets, are prevalent throughout the region. The intense gravitational forces and radiation emanating from Sgr A* appear to drive the creation of larger, more complex molecules than those found in quieter regions of space. This international ACES initiative brings together over 160 researchers from more than 70 institutions, including Professor Mattia Sormani of the University of Insubria, who leads the theoretical data processing group.

Professor Christoph Federrath from the Australian National University (ANU) emphasized that the gas targeted by ACES represents the cold molecular fuel necessary for stellar development, noting that the CMZ is a far more extreme environment than the outer reaches of the Milky Way. The debut of this ALMA mosaic marks a significant technological and scientific milestone in observational astrophysics. By mapping molecular chemistry across such a vast and volatile area, scientists now have the empirical data needed to test theories of galactic evolution and the origins of complex chemistry. Looking ahead, the scientific community anticipates even deeper insights from the upcoming ALMA Wideband Sensitivity Upgrade and the ESO’s Extremely Large Telescope (ELT).