Disk fragmentation in high-mass star formation

Abstract

Context. Increasing evidence suggests that, similar to their low-mass counterparts, high-mass stars form through a disk-mediated accretion process. At the same time, formation of high-mass stars still necessitates high accretion rates, and hence, high gas densities, which in turn can cause disks to become unstable against gravitational fragmentation. Aims. We study the kinematics and fragmentation of the disk around the high-mass star forming region AFGL 2591-VLA 3 which was hypothesized to be fragmenting based on the observations that show multiple outflow directions. Methods. We use a new set of high-resolution (0 . 19) IRAM/NOEMA observations at 843 µm towards VLA 3 which allow us to resolve its disk, characterize the fragmentation, and study its kinematics. In addition to the 843 µm continuum emission, our spectral setup targets warm dense gas and outflow tracers such as HCN, HC 3 N and SO 2 , as well as vibrationally excited HCN lines. Results. The high resolution continuum and line emission maps reveal multiple fragments with subsolar masses within the inner ∼1000 AU of VLA 3. Furthermore, the velocity field of the inner disk observed at 843 µm shows a similar behavior to that of the larger scale velocity field studied in the CORE project at 1.37 mm. Conclusions. We present the first observational evidence for disk fragmentation towards AFGL 2591-VLA 3, a source that was thought to be a single high-mass core. While the fragments themselves are low-mass, the rotation of the disk is dominated by the protostar with a mass of 10.3±1.8 M . These data also show that NOEMA Band 4 can obtain the highest currently achievable spatial resolution at (sub-)mm wavelengths in observations of strong northern sources.

Infrared H2O Absorption in Massive Protostars at High Spectral Resolution: Full Spectral Survey Results of AFGL 2591 and AFGL 2136

“…As an aside, we note that the high densities inferred (>10 10 cm −3 ) from the similarity in the rotational and vibrational H 2 O excitation temperatures would suppress H 2 O maser emission (Kaufman & Neufeld 1996;Hollenbach et al 2013). Submillimeter observations of AFGL 2591 have revealed emission of vibrationally excited HCN but this emission was associated with the disk rather than foreground material (Suri et al 2021).…”

“…High-resolution observations with the Northern Extended Millimeter Array of these lines suggest a rotating disk structure in AFGL 2591 with a radius of ∼1000 au and a northeast-southwest velocity gradient, which is not in perfect Keplerian rotation. This disk has fragmented into three companion cores with separations of 800 and 1400 au (Suri et al 2021).…”

“…As their velocity is close to the systemic velocity and they are at ∼125 au (Frost et al 2021) from a 45 M e star (Maud et al 2019), the motion of these blobs is mainly transverse; e.g., either in the front or the back of the disk. On a 1000 au scale, AFGL 2591 also shows a complex dynamical environment with a Keplerian rotating disk containing multiple cores that could evolve into companions (Suri et al 2021). In general, the complex morphology with spiral arms and subcondensations revealed by submillimeter observations of disks around massive protostars may reflect Toomre instability (Maud et al 2019;Johnston et al 2020;Suri et al 2021).…”

“…On a 1000 au scale, AFGL 2591 also shows a complex dynamical environment with a Keplerian rotating disk containing multiple cores that could evolve into companions (Suri et al 2021). In general, the complex morphology with spiral arms and subcondensations revealed by submillimeter observations of disks around massive protostars may reflect Toomre instability (Maud et al 2019;Johnston et al 2020;Suri et al 2021). This large-scale structure likely persists into the inner disk, and in this scenario, mid-IR absorption lines would be attributed to bright (dust emission) spots therein.…”

A scaled-up planetary system around a supernova progenitor

“…Recent updates of the classical CA model, such as pebble accretion, have been indicated as a possible solution to the conundrum (Lambrechts & Johansen 2012) 18 On the other hand, giant planets may possibly form inside massive protoplanetary disks on a much shorter timescale of ∼ 10 4 yr by means of GI. While this mechanism is not likely to be at the origin of most planets observed around solar-type stars, it might be considered for stars much more massive than the Sun; there is observational evidence of disk fragmentation around 10 M stars (Cadman et al 2020;Suri et al 2021). GI preferentially produces massive planets in wide orbits, although rapid migration can force some of them to move much closer to the star (Malik et al 2015).…”