An international consortium of astronomers conducted an in-depth mapping of the Milky Way’s core utilizing the ALMA (Atacama Large Millimeter/submillimeter Array) radio interferometer. The primary objective was to pinpoint the reasons for the unexpectedly low rate of star formation within a region dense with gas and dust. This survey, named the ALMA Central Molecular Zone Exploration Survey (ACES), encompassed nearly the entire central sector of the galaxy, spanning approximately 650 light-years.
The observational focus was situated around the supermassive black hole, Sagittarius A*. This locale harbors tens of millions of solar masses of compact material and is characterized by elevated temperatures and intense turbulence. Conventional theoretical frameworks predict that such an environment should foster robust new star genesis; nevertheless, the actual pace of this creation is roughly ten times less than anticipated.
To compile the necessary data, the research group employed a mosaic scanning technique, integrating thousands of discrete observations into a singular, comprehensive map. This methodology successfully merged high angular resolution with extensive spatial coverage. Consequently, the team could resolve fine structures down to individual dense clumps potentially capable of gravitational collapse, while simultaneously preserving details about large-scale gas flows.
Source: ESO / NAOJ / NRAO / S. Longmore et al. / D. Minniti et al.
Furthermore, spectral lines from over 70 distinct molecules, including silicon monoxide, methanol, and acetone, were spectroscopically measured. These compounds are sensitive indicators of differing physical conditions and serve as diagnostic tools for assessing density, temperature, and the presence of shock waves. Correlating their spatial distribution permitted the tracing of gas compression zones, regions influenced by radiation, and the repercussions of energetic outflows from massive stars.
According to astronomer Ashley Barnes from the European Southern Observatory (ESO), this fresh dataset offers, for the first time, a coherent structural depiction of the Central Molecular Zone without compromising fine-scale detail. Prior surveys either covered broader areas at lower resolution or zeroed in on isolated clouds, thus precluding analysis of process interconnections.
The gathered observational evidence was subsequently cross-referenced with numerical models simulating gas movement along the galactic bar, the accretion dynamics of dust clouds, and their reciprocal interaction with stellar radiation and supernova explosions. These models were transformed into synthetic maps and directly benchmarked against the survey outcomes, allowing for the testing of different evolutionary scenarios for matter within the galactic nucleus.
Project lead Steve Longmore of Liverpool John Moores University highlighted that the Central Molecular Zone is the birthplace of some of the Milky Way’s most massive stars, a fraction of which conclude their lives as hypernovae—explosions whose energy output surpasses that of a typical supernova by more than tenfold. These energetic events significantly shape gas dynamics and are capable of suppressing subsequent star formation.
The authors intend to leverage the complete data archive to investigate precisely where in the gas flow star collapse is initiated or halted, and how gravity, turbulence, and energetic feedback mechanisms are interrelated. They estimate that the conditions in the Milky Way’s center closely resemble those found in the early universe atmospheres, lending significant weight to these findings for understanding galactic evolution universally.
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