High-mass stars control the dynamics and chemistry of our Galaxy. They are crucially responsible for processing higher elements. The formation of very massive stars - similar to any other star such as Sun -take place through gravitational collapse of dense clouds of gas and dust - however, at a much rapid pace and violent conditions. It involves high accretion rates, very dense accretion flows quickly fragmenting to secondary pre-stellar cores and an early onset of nuclear fusion. How do such extreme conditions influence the physics of high-mass star formation is a fore-front question in modern astrophysics. Theoretical studies and numerical simulations deliberate scenarios of this physics - yet to be tested in detail by observations. The objectives of this project were to conduct specific observations, tailored to test front-line scenarios of high-mass star formation.
A forming star is known to gain mass through episodic accretion events, rather than accretion flows (constant influx of material). Episodic accretion leads to the variable brightness well-known in low-mass young stars, including the extreme cases of FU-Ori type bursts. Such variations are hitherto unknown in high-mass stars. Our objective is to search for this variability using the VISTA VVV survey data.
Accretion flows forming high-mass stars are extremely dense, therefore, quickly become Jeans unstable and fragment into secondary stellar seeds. This seed competes with the primary, to gain mass from the common reservoir, setting an upper limit on how massive a star can become. Our aim is to examine the physics of this scenario using detailed observations of prototypical high-mass systems.
A high-mass protostar is subject to an enormous level of internal energy derived from Kelvin-Helmholtz contraction and early nuclear burning. It is also fed with high entropy material from the disk. It has been suggested that the high entropy drives the massive protostars to bloat/puff up during most of its formation phase as it adjusts itself. A bloated massive star will then have a cooler photosphere, albeit being luminous. We want to search for signatures of the bloated cooler and luminous photospheres in young massive stars.
