In a kitchen where you're simultaneously boiling soup, frying meat, and baking bread, everything happens in one pot. That's roughly what the central molecular zone (CMZ) looks like — a dense clump of gas at the very heart of the Milky Way. Here, just a few hundred light-years from the supermassive black hole Sagittarius A*, the gas behaves strangely: it compresses, heats up, and collides with itself.
The new ACES survey, carried out with the ALMA radio telescope, lets us see this "pot" in unprecedented detail, with a resolution of 0.1 parsec — about 0.3 light-years, or 30 times the distance from the Sun to Pluto. The telescope simultaneously captured emission from five different molecules and atoms. Each "signature" tells its own story: CS (carbon disulfide) marks dense, cold clumps; SO (sulfur monoxide) highlights regions where gas is violently compressed by shock waves; and H40α (hydrogen radio recombination line) traces hot, ionized bubbles around young stars. Together, they paint a map where calm regions sit next to zones of vigorous star formation.
The scientists found that the chemical composition of the gas varies dramatically from place to place. Where clouds collide, carbon disulfide nearly disappears, while sulfur monoxide shines brightly. And near young, hot stars, the gas becomes ionized and glows in the radio band like a neon sign. This mosaic of conditions is key to understanding how stars form in the Galactic center and why the process differs from that in the quiet outskirts.
These data are just the first step. Ahead lies a detailed analysis of gas motions, a search for hidden stellar nurseries, and possibly the answer to how matter feeds the black hole at the center. The pot on the Galaxy's kitchen stove is boiling, and now we have a recipe to understand its churn.
The central molecular zone is so dense that if the Solar System were placed inside it, the night sky would glow with hundreds of bright nebulae, and the interstellar gas would be visible to the naked eye as a faint glow.
In Isaac Asimov's novel "The Gods Themselves," aliens live in a dense medium similar to the central molecular zone, where gas is so thick it forms peculiar "mountains" and "oceans."