Mining the ALMA Archive for Massive Young Stellar Object Accretion Bursts

High-mass stars (stars with masses more than 8 times that of the Sun) are central to our understanding of the Universe. Their formation and early evolution impact almost every area of astrophysics, from planet formation (with most stars, and hence planets, forming in clusters near high-mass stars) to galaxy evolution and cosmology. How high-mass stars form, and the physical mechanism(s) by which they accumulate their large masses, are among the key open questions in astrophysics.

For decades, it has been known that Sun-like low-mass stars experience bursts of accretion, during which material from the surrounding disc falls onto the star at a higher rate. This results in an increase in the total luminosity (brightness) of the forming star, hence the term "burst". Until recently, however, there was no observational evidence for a similar phenomenon in forming high-mass stars.

This changed in 2016/17, when increases in luminosity attributed to accretion bursts were reported towards two forming high-mass stars. This discovery has prompted an outpouring of research, including new theoretical models of high-mass star formation incorporating accretion bursts and concerted efforts to identify additional outbursts from forming high-mass stars. Despite these efforts, to date only two additional high-mass sources have been identified.

The aim of this project is to conduct the first large-scale systematic search for accretion bursts in young high-mass stars. The project is possible now (and only now) because of three key things: (1) the change in brightness caused by an accretion burst is detectable at millimetre wavelengths,

(2) the world-leading facility known as the Atacama Large Millimeter/submillimeter Array (ALMA) can distinguish the emission from different massive protostars within the same protocluster,

and (3) the COVID pandemic disrupted the observations of ALMA in a way that created a unique set of observations of young high-mass stars separated in time by months to years.

In this project, we will process and analyse separately multiple epochs of ALMA observations for many hundreds of young high-mass stars, searching for the changes in brightness that indicate an accretion burst. Where these bursts are found, we will carry out additional observations with ALMA and other mm-wavelength telescopes to study the properties of the bursts, to add to the small (4 objects) sample of known accretion bursts from young high-mass stars.

We will compare the statistics on accretion bursts in young high-mass stars resulting from our studies to the new theoretical models, to better understand which of the suggested mechanisms -- which range from instabilities in the discs to the disruption of planet-like objects -- are causing the observed accretion bursts.