New study maps ripples and hidden structures in southern Milky Way
by Clarence Oxford
Los Angeles CA (SPX) Sep 07, 2025

Astronomers have produced the most detailed 3D map yet of the Milky Way's cold gas clouds, revealing large-scale ripples in the Galaxy's midplane and identifying a new structure at the far end of the central bar. The work comes from the Three-millimeter Ultimate Mopra Milky Way Survey (ThrUMMS), led by Peter Barnes of the Space Science Institute.

Spiral galaxies like the Milky Way are generally flat, but the team found that the Galaxy's cold gas distribution is warped into a wave-like pattern. These ripples in the disk may have been triggered by a gravitational encounter with the Sagittarius Dwarf Galaxy about 200 million years ago, leaving the Milky Way "ringing like a bell."

In addition, the researchers discovered a set of clouds in the constellation Ara, about 35,000 light-years away, now termed the Far Ara Clouds. These are likely located at the distant end of the Milky Way's bar, a feature only recognized in the last two decades. The bar's ends act as transition zones where circular and plunging orbits intersect, creating mass pileups and stimulating intense star formation.

The findings highlight both the dynamic nature of the Galaxy and the challenges of understanding its structure from within. By combining distance measurements and careful mapping of gas clouds, ThrUMMS is offering astronomers an unprecedented look into the architecture driving the Milky Way's evolution.

Research Report:The Three-mm Ultimate Mopra Milky Way Survey. III. Data Release 6, An Atlas of Physical Conditions, Global Mass Conversion Laws, and 3D Physical Architecture of the Molecular Interstellar Medium in the Fourth Quadrant

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