Largest ALMA Mosaic Reveals Milky Way's Chaotic Core

New radio image captures intricate web of cold gas and star-forming structures in the galaxy's central region.

Published on Feb. 28, 2026

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Astronomers have released the largest-ever mosaic image from the Atacama Large Millimeter/submillimeter Array (ALMA), showcasing the complex distribution of molecular gas in the Central Molecular Zone (CMZ) at the heart of the Milky Way. The image reveals a tangle of cold, threadlike gas structures and chemical fingerprints scattered throughout the scene, providing unprecedented detail on the extreme conditions in this region surrounding the supermassive black hole at the galactic center.

Why it matters

The CMZ is the dense, dusty core of our galaxy, where gravity, turbulence, shocks, magnetic fields, and rapid rotation all interact, making it a unique laboratory for studying how gas turns into stars in a chaotic environment. Understanding star formation in the CMZ can also shed light on how galaxies evolved in the early universe, when conditions were more extreme than in today's galactic discs.

The details

The ALMA mosaic covers an area spanning more than 650 light-years across, large enough to capture sweeping structures while also resolving individual star-forming clouds. It is part of the ALMA CMZ Exploration Survey (ACES), which aims to track the complex physical and chemical processes driving star birth in this extreme region. The image highlights the distribution of five different molecules, each tracing different conditions in the gas. Astronomers have already identified several intriguing features, including an expanding ring of dense, shocked gas and a compact source with exceptionally broad molecular line emission that lacks obvious counterparts at other wavelengths.

  • The ALMA mosaic is the largest image ever assembled from ALMA observations.
  • The ACES survey was designed to provide uniform ALMA Band 3 coverage across the inner CMZ at an angular resolution of about 1.5 arcseconds.

The players

Ashley Barnes

An astronomer at the European Southern Observatory (ESO) in Germany and part of the team behind the ACES project.

Steve Longmore

A professor of astrophysics at Liverpool John Moores University in the UK and the leader of the ACES project.

Katharina Immer

An ALMA astronomer at ESO who is also part of the ACES project.

Atacama Large Millimeter/submillimeter Array (ALMA)

An international astronomical observatory located in the Atacama Desert of northern Chile, of which ESO is a partner.

Central Molecular Zone (CMZ)

The dense, dusty heart of the Milky Way galaxy, where a supermassive black hole is located and extreme conditions prevail.

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What they’re saying

“It's a place of extremes, invisible to our eyes, but now revealed in extraordinary detail.”

— Ashley Barnes, Astronomer, European Southern Observatory (thebrighterside.news)

“By studying how stars are born in the CMZ, we can also gain a clearer picture of how galaxies grew and evolved.”

— Steve Longmore, Professor of Astrophysics, Liverpool John Moores University (thebrighterside.news)

“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.”

— Katharina Immer, ALMA Astronomer, European Southern Observatory (thebrighterside.news)

What’s next

The team says the ACES results are being presented across multiple papers, with five accepted in Monthly Notices of the Royal Astronomical Society and a sixth in the final review stages. Upcoming upgrades to ALMA's sensitivity and the future Extremely Large Telescope could provide even more detailed insights into the complex chemistry and dynamics of the Milky Way's central region.

The takeaway

The ALMA mosaic of the Milky Way's Central Molecular Zone reveals the extreme, chaotic conditions at the heart of our galaxy, where star formation occurs under the influence of a supermassive black hole and other powerful forces. Understanding this unique environment can shed light on how galaxies evolved in the early universe and the complex processes that govern the birth of stars.