A protostar reveals a new scenario for planetary formation

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An international team of astronomers, involving researchers of the IPAG-OSUG (CNRS / Université Joseph Fourier Grenoble I) and the IRAP-OMP (CNRS / Université Paul Sabatier Toulouse III), observed for the first time the protostar L1527 at a very high spatial resolution using the interferometer ALMA1. The researchers were able to demonstrate a chemical change in the composition of the protostar, challenging the planetary formation scenarios. These results appear on Feb. 13 in the journal Nature.

Between the moment a gas cloud collapses under its own weight to form a star and the formation of the protoplanetary disk, several stages follow one another. Initially, the protostar L1527, located in the Taurus molecular cloud, is buried in a thick dust shell. Gradually, the envelope decreases, and finally when the envelope has totally disappeared, the protoplanetary disk becomes visible. Planets can then be formed therein.

(left) Illustration of the envelope collapsing and rotating around the protostar. (middle): Representation of the model used in the paper. (right): Agreement between the observations of the molecule c-C3H2 and the model. Crédits : Sakai et al.

The process of formation of the disk of gas and the associated chemical changes remained unexplored observationally until today. Through the observations of the c-C3H2 and SO species, the team discovered an unexpected chemical change in the transition zone between the collapsing envelope and the disk of gas. Indeed, c-C3H2 completely disappears at about 100 astronomical units corresponding to the centrifugal barrier while SO exists only in a ring located at the same distance. Until now it was thought that the interstellar matter was brought to the disk regularly without any significant change in the chemical composition. But it now appears that this assumption was not true. This chemical change indicates that the outer edge of the disk of gas expands. The solar system has probably undergone the same change during its development and this study provides an important element in our understanding of the formation of our own planetary system.


  1. ALMA is a high technology interferometer that allows to explore the objects in the Universe, in the millimeter and submillimetre domains with high sensitivity and an angular resolution similar to that of the Hubble Space Telescope. It is the largest existing project for ground-based astronomy. ALMA is a partnership between Europe, North America and East Asia in cooperation with the Republic of Chile. It was inaugurated in March 2013 but observes since 2011.http://www.almaobservatory.org/


IRAP Contact :

  • Charlotte Vastel, IRAP (CNRS/Université Paul Sabatier-Toulouse III)
    cvastel@irap.omp.eu, 05 61 55 75 44



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