The young binary star IRS 44 in the constellation Ophiuchus resembles a bustling kitchen: streams of gas, like jets of dough, fall onto a rotating disk, and where they strike, heat is born. New high-resolution observations have for the first time shown that these collisions are the cause of the unusual glow of sulfur molecules.
Astronomers pointed the ALMA array at the system and saw two stars — IRS 44 A and IRS 44 B. Around the second star, gas falls faster. When the stream slams into the outer edge of the gas-and-dust disk, it decelerates abruptly, and the energy of the impact heats the dust. The heat evaporates sulfur oxide molecules (SO and SO₂) from the dust grain surfaces: their emission flares brightly precisely in the collision zone.
Almost all the carbon in this system is locked up in carbon monoxide (CO), so there isn't enough free carbon to form other molecules. But there is plenty of oxygen and sulfur: in the hot gas, they combine to form SO and SO₂. This explains why IRS 44 B has so many sulfur oxides and so few carbon-sulfur compounds.
The observations also showed that star B is embedded in denser gas than star A. Perhaps they were not born at the same time, or B has been "rejuvenated" by late infall of material. This picture helps us understand how stars in binary systems influence each other even before birth.
Thus, shock waves at the disk boundary turned out to be the key to the chemistry of a young system. Gas falling from the outskirts doesn't just feed the star: it heats the dust, releases sulfur, and leaves little room for carbon molecules in the oxygen-rich environment. Now this mechanism can be sought in other protostars.
Shock waves in IRS 44 B heat the dust so much that sulfur evaporates from its surface, like water from a hot skillet, but on a cosmic scale.
In Stanisław Lem's novel "Solaris," the planet's ocean generates complex structures; here, gas streams around a young star create chemical "islands" of sulfur that could become building material for future planets.