Gas infall via accretion disk feeding Cepheus A HW2

TL;DR

This study provides direct observational evidence of a gaseous accretion disk around the young massive star HW2 in Cepheus A, demonstrating high mass infall rates and disk kinematics that support ongoing star formation.

Contribution

First direct resolution of the accretion disk around HW2 using sensitive NH3 observations, confirming its role in high-rate mass infall in a massive star.

Findings

Mapped the accretion disk at 200-700 au radii

Measured high infall rates of 2×10^{-3} M_sun/yr

Supported by simulations showing efficient mass focusing

Abstract

The star-forming region Cepheus A hosts a very young star, called HW2, that is the second closest to us growing a dozen times more massive than our Sun. The circumstellar environment surrounding HW2 has long been the subject of much debate about the presence or not of an accretion disk, whose existence is at the basis of our current paradigm of star formation. Here, we answer this long standing question by resolving the gaseous disk component, and its kinematics, through sensitive observations at cm wavelengths of hot ammonia (NH$_3$) with the Jansky Very Large Array. We map the accretion disk surrounding HW2 at radii between 200 and 700 au, showing how fast circumstellar gas collapses and slowly orbits to pile up near the young star at very high rates of $2\times10^{-3}$ M$_{\odot}$ yr$^{-1}$. These results, corroborated by state-of-the-art simulations, show that an accretion disk is still efficient in focusing huge mass infall rates near the young star, even when this star has already reached a large mass of 16 M$_{\odot}$.