Visualization of the unstable accretion disk around a forming massive star. Credit: Institute for Astronomy and Astrophysics, Tübingen University
“How do massive stars form?” is one of the fundamental questions in modern astrophysics, because these massive stars govern the energy budget of their host galaxies. Using numerical simulations, Professor Wilhelm Kley et al from Institute for Astronomy and Astrophysics, University of Tübingen, with Dr. Vorobyov from Institute for Astrophysics, University of Vienna revealed new components of the formation of massive stars, already known from the formation process of low-mass and primordial stars.
The birth of massive stars is still a mystery to us, because these stars are embedded in an extremely dense medium of gas and dust. This opaque envelope makes it difficult to directly observe the birth process even with modern telescopes. Therefore, the researchers modeled the birth process within a numerical simulation. For this ambitious, computationally expensive study they made use of high-performance computers within the bwHPC initiative of the state of Baden-Württemberg.
The simulation starts with a cloud of gas and dust, which collapses under its own gravity and eventually forms a accretion disk around the hot young star. The material in such a disk rotates around the central star and slowly transports gas and dust towards it. For the first time, the resolution of these simulations was sufficient to infer formation of high-density clumps within the unstable disk. Once formed, these clumps start to migrate through the disk and finally sink into the central star. “Like throwing logs into a fireplace, these episodes of clump consumption produce violent luminosity outbursts outshining the collective effect of 100 000 Suns,” says Eduard Vorobyov.
A similar process of episodical luminosity bursts was already known with respect to the formation of the first stars in the Universe and for low-mass stars like our Sun. The new investigation suggests now the formation of stars of any kind and epoch are controlled by the same universal processes: The clumps are excellent candidates for the formation of Solar-type companions to massive stars: “These companions will also influence their future evolution.”
The results will help to develop new observing strategies for detecting these luminosity outbursts – and even for directly imaging the high-density clumps in accretion disks around very young massive stars. This will be a task for modern observing facilities such ALMA of the European Southern Observatory (ESO) or the future European Extremely Large Telescope (E-ELT).
https://www.uni-tuebingen.de/en/newsfullview-landingpage/article/die-geburt-massereicher-sterne-wird-von-leuchtkraeftigen-helligkeitsausbruechen-begleitet.html
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