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In an oven, a huge loaf of bread is baking. Inside the dough, there is a tiny, hottest spot: that's where the future loaf begins to rise. A hot molecular core (a region the size of the Solar System, where gas is heated to hundreds of degrees and compressed to billions of times the density of ordinary clouds) works in much the same way. Hidden inside is the embryo of a massive star, and astronomers are trying to peek into this "oven" without opening the door.

The team pointed the antennas of the ALMA radio telescope at the core AG318-c9, located 10.4 kiloparsecs away (about 34,000 light-years — light has been traveling to us longer than human civilization has existed). They collected radiation in the range of about 220 gigahertz, like listening to a very high note emitted by the gas itself. Using the MADCUBA software, the astronomers deciphered this "melody" and identified lines from dozens of substances, including three familiar organic molecules: ethylene glycol (a component of antifreeze), glycolaldehyde (the simplest sugar), and methyl formate (which smells like rum).

Then came the detective work: the researchers built pixel-by-pixel maps of the emission for each of the three molecules. It turned out that all of them, like glowing paint, outline the hottest and densest heart of the core. Moreover, the maps from different molecules almost coincide, so any one of them serves as a reliable marker of the hidden center. Comparison with another well-known core, G31.41+0.31, showed that this pattern is not random: the chemical fingerprint of hot cores repeats from object to object.

Now astronomers have a simple and fast way to find the most active sites of star formation: just map one of the three molecules. It's like skipping the tedious measurement of temperature in every corner of the oven and simply looking at where the dough has browned the most.

Original abstract

as written by the authors arXiv:2606.07388

We present a detailed molecular line analysis of one of the most chemically rich cores in the ALMAGAL sample, the high-mass core~9 in the AG318.9477-00.1960 clump (AG318-c9), located at a heliocentric distance of \sim 10.4\,\rm kpc. We further assessed whether the emission of selected COMs, that is, ethylene glycol ((CH_2OH)_2; EG), glycolaldehyde (CH_2(OH)CHO; GA), and methyl formate (CH_3OCHO; MF), can be used to trace the innermost regions of hot molecular cores (HMCs). We analysed ALMA Band~6 observations (\sim 217-221GHz). Spectral line identification and local thermodynamic equilibrium modelling were performed using the software MADCUBA. We derived the physical parameters, including the column density (N), excitation temperature (Tex), velocity, line width, and molecular abundances relative to H_2, for all detected species. The chemical inventory of AG318-c9 was compared with that of the HMC G31.41+0.31 (G31). In addition, we performed a pixel-by-pixel analysis of EG, GA, and MF to generate spatially resolved N and Tex maps and corresponding radial profiles.