From SRON: “Supermassive stars also formed from circumstellar discs”
13 February 2017
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Artist’s impression of a disk around an O-type protostar. No image credit.
Supermassive stars also appear to be formed in a process that involves rotating circumstellar discs of dust, just like their smaller siblings with a ‘normal’ mass. This was revealed in new research by 24 scientists, among whom was Floris van der Tak (SRON), who wanted to know why stars do not all evolve to be the same.
When a sun-like star is born from a cloud of gas and dust, the dust and gas do not fall directly onto the growing baby star. Dust that comes near the star first rotates in a disc around this protostar and is then added to the star via the disc. However, besides the very frequently occurring stars like our sun, there are also stars from far more massive categories, the biggest of which is the O-type. Such stars are at least ten times heavier than our sun.
The researchers wondered whether they could also observe the birth of these heavy types of stars somewhere in the universe, and whether discs of dust revolved around these as well. If such discs were present, then they wanted to know how the properties of the discs of baby suns differed from those of their heavier family members.
In 2015, the birth of such a heavy O-type star with a circumstellar disc had already been observed. The 24 researchers, led by Riccardo Cesaroni, have now described four more stars. They used the ALMA telescope in Chile to observe the stars in the infrared spectrum, which allowed them to observe the rotating discs as well.
The heavy discs weigh about half of the protostar’s mass. That is a lot: in the case of sun-like protostar, the disc weighs about 1 to 10 percent of the protostar’s mass.
“Furthermore, such weight makes the heavy discs unstable due to their own gravity. That might explain why this type of star can be far heavier than sun-like stars,” says Van der Tak.
The researchers published their results in the renowned journal Astrophysics & Astronomy. A pre-print is already available at http://www.arcetri.astro.it/science/starform/preprints/cesa_29.pdf
See the full article here .
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