At the center of the distant galaxy NGC 1052, an invisible engine is at work. It accelerates clouds of gas to speeds at which sulfur oxide (SO) molecules begin to absorb radio waves. Astronomers caught this radiation using a network of Korean radio telescopes operating as a single instrument the size of a continent.
The supermassive black hole at the galaxy's core is surrounded by a rotating ring of gas and dust — a torus. A plasma jet emerging from the vicinity of the hole plows into this ring. The impact heats the gas, and SO molecules evaporate from the surfaces of dust grains. Some clouds are carried away by the jet, while others, having lost speed, fall back toward the hole.
Previously, water vapor masers, natural cosmic amplifiers of radio waves, had been found in the same region. Now it turns out that both SO molecules and H2O masers arise in the same collision zone where the jet meets the torus. The only difference is that water amplifies radiation, while sulfur oxide absorbs it.
Thus, astronomers have for the first time peered into a region less than half a light-year across around the black hole. It turns out that gas there is not simply falling into the hole but participates in a complex cycle: the jet flings it outward, gravity pulls it back. This "breathing" process may govern the black hole's growth and the birth of new stars in the galaxy.
as written by the authors arXiv:2601.03530
We report the first {\lambda}2-mm very long baseline interferometry (VLBI) observations of the radio galaxy NGC 1052, conducted with the Korean VLBI Network (KVN) using a wide-band recording mode. Leveraging the wide bandwidth covering a velocity range at 2300 km/s, we successfully detect broad (> 700 km/s) multi-component SO J_N = 3_3 - 2_2 absorption against the sub-parsec-scale continuum structure. The absorption profile consists of both redshifted and blueshifted components, including a newly identified blueshifted feature at -412 km/s relative to the systemic velocity. Significant SO absorption is confined to the central components, with no substantial detection toward the outer jet components. This constrains the location of SO gas to a compact region smaller than 0.45 pc in the sub-parsec vicinity of the supermassive black hole (SMBH). Our results support the scenario in which SO molecules are evaporated through shock heating caused by jet-torus interaction. The SO gas clumps are likely driven outward by the jet, with some returning toward the SMBH as inflowing material. Comparison with 321 GHz H2O masers reveals partial similarities in spatial distribution and radial velocity, suggesting that the jet-torus interaction may also trigger the excitation of H2O masers.
Sulfur oxide (SO) molecules are rare in space. On Earth, this compound forms when sulfur burns, and it is familiar to anyone who has lit a match.