Understanding Accretion Outbursts in Massive Protostars through Maser Imaging

TL;DR

This paper discusses how maser imaging at centimeter wavelengths can reveal the dynamics of accretion and outbursts in massive protostars, challenging traditional models and guiding future observations.

Contribution

It highlights the importance of maser imaging for understanding episodic accretion outbursts in massive star formation and proposes the need for more sensitive interferometers.

Findings

Maser flares can signal accretion outbursts in high-mass protostars.

High-resolution imaging can resolve motions below 1 au in embedded regions.

Future observations will identify progenitors and quantify outburst effects.

Abstract

The bright maser emission produced by several molecular species at centimeter to long millimeter wavelengths provides an essential tool for understanding the process of massive star formation. Unimpeded by the high dust optical depths that affect shorter wavelength observations, the high brightness temperature of these emission lines offers a way to resolve accretion and outflow motions down to scales below $\sim$1 au in deeply embedded Galactic star-forming regions at kiloparsec distances. The recent identification of extraordinary accretion outbursts in two high-mass protostars, both of which were heralded by maser flares, has rapidly impacted the traditional view of massive protostellar evolution, leading to new hydrodynamic simulations that can produce such episodic outbursts. In order to understand how these massive protostars evolve in response to such events, larger, more sensitive ground-based centimeter wavelength interferometers are needed that can simultaneously image multiple maser species in the molecular gas along with faint continuum from the central ionized gas. Fiducial observations of a large sample of massive protostars will be essential in order to pinpoint the progenitors of future accretion outbursts, and to quantify the outburst-induced changes in their protostellar photospheres and outflow and accretion structures. Knowledge gained from these studies will have broader impact on the general topic of accretion onto massive objects.