Alcohol in the Galaxy's Ice: What the Center of the Milky Way Hides express
At the center of our Galaxy lies a dense forest of dust and gas. Starlight barely penetrates this thicket, like a flashlight in fog. But it is precisely there, in this dense cloud, that new stars are born.
Scientists decided to look into this fog. They took light from 15 bright stars that shine through cold clouds. The ice on dust grains in these clouds leaves its imprint on the light, like fingerprints. From these imprints, one can tell what the ice is made of.
It turned out that in the Galactic center, the ice is poor in methanol — a simple alcohol. In other parts of the Milky Way, there is more of it. Why? Possibly, young stars here are so hot that they evaporate methanol from their outskirts, just as the sun dries up puddles after rain.
This discovery helps understand how planets are born. After all, comets and planets are assembled from such icy dust grains. If the ices in the Galactic center are different, then planets there might be different too.
Original abstract
as written by the authors arXiv:2601.05507
The Central Molecular Zone (CMZ) contains a substantial reservoir of dense molecular gas, where numerous young stellar objects (YSOs) and dense cloud cores have been identified. However, the large distance and severe foreground extinction complicate interpretation of infrared ice absorption features tracing chemical and evolutionary properties of these embedded objects. To better characterise YSOs and dense cores in this region, we combined spectra from multiple YSOs, each likely backlit by a giant star, allowing us to probe their outer layers and derive an ensemble-averaged ice abundance profile. We obtained L-band spectra of 15 point-like sources with extremely red colours using Gemini/GNIRS, enabling measurements of the CH3OH absorption feature at 3.535 micron. To better constrain the foreground extinction and H$$_2$$O ice column densities, we combined these data with K-band and mid-infrared spectra using NASA/IRTF and Spitzer/IRS. We found that the CH$$_3$$OH abundance in the CH$$_3$$OH-CO$$_2$$ ice mixture is 2 to 5 percent, confirming that it is systematically lower than those typically observed in the Galactic disk. Furthermore, by using the local excess of foreground extinction as a proxy for the projected distance between a backlit source and the centre of a YSO, we found that the CH$$_3$$OH abundance relative to solid CO$$_2$$ remains near 10 percent in the inner regions of the envelope, but increases sharply to about 30 percent in the outer regions. The relatively low methanol ice abundance may reflect the unique chemical environment of the CMZ. However, our results offer an alternative interpretation: since our sample is biased towards massive and luminous YSOs, intense heating from the central protostar may have caused substantial sublimation of methanol ice in the inner regions of their envelopes, thereby systematically lowering the observed CH$$_3$$OH/H$$_2$$O ice ratios.
In space, more than 200 different molecules have been found, and methanol is one of the most common. In warm clouds, it forms more complex organic substances, the building blocks of life.