Discovery of a sub-Keplerian disk with jet around a 20 M⊙ young star

A Sanna,L Moscadelli,A Kölligan,R Kuiper,C Goddi,Q Zhang,R Cesaroni,S Leurini,A Caratti O Garatti,C Carrasco-González,K M Menten,T Pillai

doi:10.1051/0004-6361/201833411

Abstract

It is well established that solar-mass stars gain mass via disk accretion, until the mass reservoir of the disk is exhausted and dispersed, or condenses into planetesimals. Accretion disks are intimately coupled with mass ejection via polar cavities in the form of jets and less collimated winds, which allow mass accretion through the disk by removing a substantial fraction of its angular momentum. Whether disk accretion is the mechanism leading to the formation of stars with much higher masses is still unclear. Here, we are able to build a comprehensive picture of the formation of an O-type star by directly imaging a molecular disk, which rotates and undergoes infall around the central star, and drives a molecular jet that arises from the inner disk regions. The accretion disk is truncated between 2000 and 3000 au, it has a mass of about a tenth of the central star mass, and is infalling towards the central star at a high rate (6 × 10−4 M⊙ yr−1), so as to build up a very massive object. These findings, obtained with the Atacama Large Millimeter/submillimeter Array at 700 au resolution, provide observational proof that young massive stars can form via disk accretion much like solar-mass stars.

Highlights

Models of massive star formation in the disk accretion scenario predict that circumstellar disks could reach radii between 1000 and 2000 au (e.g., Krumholz et al 2007; Kuiper et al 2011; Harries et al 2017)
We have simulated the disk appearance for our specific observational conditions, and produced synthetic maps of the line and dust emission around the young star, in order to compare the observed pv-diagrams with those expected under two simple assumptions: the disk is falling in towards the central star due to gravitational attraction; the disk is rotating around the central star in centrifugal equilibrium
We report on ALMA observations, at wavelengths near 1 mm, of dense molecular gas and dust in the vicinity of an O-type young star, with a linear resolution as good as 700 au and a line sensitivity of 1 K

Summary

Introduction

Models of massive star formation in the disk accretion scenario predict that circumstellar disks could reach radii between 1000 and 2000 au (e.g., Krumholz et al 2007; Kuiper et al 2011; Harries et al 2017). The interplay between disks and jets provides a mechanism to ensure mass accretion through the disk Notwithstanding their connection, there is poor evidence of disk-jet systems in the inner few 1000 au of stars with tens of solar masses (e.g., Beltrán & de Wit 2016), such as those resolved around solarand intermediate-mass stars (e.g., Lee et al 2017a,b; Cesaroni et al 2005, 2013, 2014). In order to establish the disk accretion scenario as a viable route for the formation of the most massive stars (e.g., Kuiper et al 2010), we seek to simultaneously resolve the spatial morphology of the disk and the regions where the jet originates, and to determine whether or not the disk gas is in centrifugal equilibrium. An accurate knowledge of the outflow axis allows us to pinpoint the

Results

Discussion

Conclusion