A ring/disk/outflow system associated with W51 North: a very massive star in the making

TL;DR

This study presents high-resolution observations of W51 North, revealing a massive disk, a hot molecular ring, and a collimated outflow, indicating the formation of a very massive star possibly without stellar mergers.

Contribution

First detailed high-resolution imaging of a massive protostar in W51 North, showing a disk, ring, and outflow, challenging merger-based massive star formation models.

Findings

Discovered a 3000 AU, 40 M$_\odot$ dusty disk around W51 North.

Detected a 200 M$_\odot$ collimated outflow nearly perpendicular to the disk.

Modeling suggests a central stellar mass over 60 M$_\odot$.

Abstract

Sensitive and high angular resolution ($\sim$ 0.4\arcsec) SO$_2$[22$_{2,20}$ $\to$ 22$_{1,21}$] and SiO[5$\to$4] line and 1.3 and 7 mm continuum observations made with the Submillimeter Array (SMA) and the Very Large Array (VLA) towards the young massive cluster W51 IRS2 are presented. We report the presence of a large (of about 3000 AU) and massive (40 M$_\odot$) dusty circumstellar disk and a hot gas molecular ring around a high-mass protostar or a compact small stellar system associated with W51 North. The simultaneous observations of the silicon monoxide molecule, an outflow gas tracer, further revealed a massive (200 M$_\odot$) and collimated ($\sim14^\circ$) outflow nearly perpendicular to the dusty and molecular structures suggesting thus the presence of a single very massive protostar with a bolometric luminosity of more than 10$^5$ L$_\odot$. A molecular hybrid LTE model of a Keplerian and infalling ring with an inner cavity and a central stellar mass of more than 60 M$_\odot$ agrees well with the SO$_2$[22$_{2,20}$ $\to$ 22$_{1,21}$] line observations. Finally, these results suggest that mechanisms, such as mergers of low- and intermediate- mass stars, might be not necessary for forming very massive stars.