Global collapse of a dark molecular cloud sees hundred solar mass star caught at formation

eso1331c

Images: (top) This wide-field optical view shows a region of sky in the southern constellation of Norma. At the centre lies the massive star-forming region SDC 335.579-0.292, but this is too obscured by dust to be visible. The very hot blue star HD 147937 and its surrounding ejected clouds can be seen at upper right. Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin (below) Observations of the dark cloud SDC 335.579-0.292 using the Atacama Large Millimeter/submillimeter array (ALMA) have given astronomers the best view yet of a monster star in the process of forming. A stellar womb with over 500 times the mass than the Sun has been found and appears as the yellow blob near the centre of this picture. This is the largest ever seen in the Milky Way — and it is still growing. Credit: ALMA (ESO/NRAJ/NRAO)/NASA/Spitzer/JPL-Caltech/GLIMPSE

eso1331a There are two theories on the formation of the most massive stars. One suggests that the parental dark cloud fragments, creating several small cores that collapse on their own and eventually form stars. The other is more dramatic: the entire cloud begins to collapse inwards, with material racing towards the cloud’s centre to form one or more massive behemoths there. A team led by Nicolas Peretto of CEA/AIM Paris-Saclay, France, and Cardiff University, UK, realised that ALMA was the perfect tool to help find out what was really happening. SDC335.579-0.292 was first revealed as a dramatic environment of dark, dense filaments of gas and dust through observations with NASA’s Spitzer Space Telescope and ESA’s Herschel Space Observatory. Now the team has used the unique sensitivity of ALMA to look in detail at both the amount of dust and the motion of the gas moving around within the dark cloud — and they have found a true monster. This core — the womb of the embryonic star — has over 500 times the mass of our Sun swirling around within it. The ALMA observations show that much more material is still flowing inwards and increasing the mass still further. This material will eventually collapse to form a young star up to 100 times as massive as our home star — a very rare beast.

The paper is N. Peretto et al., “Global collapse of molecular clouds as a formation mechanism for the most massive stars”, A&A, 555, A112 (2013). The data imply a huge mass infall rate of around 0.0025 solar masses per year.

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