How two young stars may draw gas from a shared reservoir

Following the gas around a young pair

How do two forming stars share the material that helps them grow? The question is especially difficult to answer for massive stars: the gas structures involved are small on the sky, and resolving the motions around each member of a young pair takes exceptionally sharp observations.

Fernando Olguin and colleagues studied two sources in the star-forming region NGC 6334I(N), using the Atacama Large Millimeter/submillimeter Array (ALMA). The objects, called ALMAe9 and ALMAe14, are separated by roughly 740 astronomical units, or 740 times the average Earth–Sun distance. The researchers treat them as a potential binary system, rather than a confirmed bound pair. At least one appears to be a growing high-mass star.

Their analysis, described in an arXiv preprint that the landing record says has been accepted for publication in The Astrophysical Journal, combines observations at a wavelength of 1.33 millimeters. The molecular-line data resolve features on a scale of roughly 90 astronomical units. That is sharp enough to investigate gas around the individual sources as well as material surrounding the pair.

Reading motion in molecular light

The team examined emission at particular frequencies from molecules including methanol. Different transitions, or changes between molecular energy levels, help trace different parts of the gas. The frequency of the received emission also carries information about motion along our line of sight: shifts in opposite directions can reveal a velocity pattern across a region.

Lower-energy methanol lines trace extended gas around the pair, out to a radius of about 1,000 astronomical units. The velocity patterns suggest a combination of rotation and possible inflow. Close to each source, the cold-gas tracers show rotation in roughly the same direction. A higher-energy methanol transition traces more compact gas near ALMAe9 and gives a rotation pattern consistent with the colder tracers. Emission from excited sulfur monoxide also traces rotation around ALMAe9.

For the secondary, ALMAe14, the authors tentatively adapt a rotation curve to estimate a central mass. The result is about two solar masses before correcting for the disk’s inclination, rather than a direct measurement of the true mass. A previous inclination-uncorrected estimate for the primary was five solar masses. The team notes that limited sensitivity in the hotter tracers and emission connecting the sources prevent a proper fit on both sides of the secondary.

Possible paths inward

The researchers identify two candidate inflows from the surrounding gas toward the individual disks. In their interpretation, emission and velocity patterns offer clues to where material could be moving inward. Excited sulfur monoxide near ALMAe14 may trace a shock where an incoming flow meets its disk, but the paper presents this as a possibility, not a direct proof of impact.

From methanol emission, the estimated rates for the two candidate flows span approximately one millionth to one ten-thousandth of a solar mass per year. These estimates depend on assumptions used to infer the gas properties and motion, and the flows themselves remain candidates. The authors also describe a third possible inflow toward the primary from gas on larger scales.

The observations provide a detailed snapshot, not a time-lapse of matter falling onto stars. Gas along the line of sight can overlap, while inclination and limited resolution complicate interpretation. Near the bright primary, strong continuum emission and optically thicker lines also make fitted gas properties less certain. The study therefore offers a plausible picture of how a shared reservoir could supply the separate surroundings of a forming pair, while leaving the geometry and nature of the proposed flows open to further investigation.