Doubts about the laws governing stellar birth

In the region behind the nebular veil, clouds of gas agglomerate and collapse, forming the progenitor structures of stars : the progenitor cores. They evolve in grous, accumulating matter and fragmenting until is formed a cluster of stars of different masses whose distribution was given Edwin Salpeter in 1955 as an astrophysical law.

Astronomers have seen that the proportion of massive objects with respect to non massive ones was the same as in stellar progenitor groups and in newly created stars. This ssggests that the mass distribution of stars when they are born, referred to as the IMF [1], just results from the mass distribution of the cores from which they are born, the so-called e CMF [2] . However, this conclusion is the fruit of the study of the molecular clouds closest to our solar system, not very dense and therefore nt representative of the various different clouds in our galaxy. Is the relation between the CMF and the IMF a universall one ? What is seen by studying denser and more distant clouds ?

These questions were raised by scientists at the Institut de planétologie et d’astrophysique de Grenoble (CNRS/Grenoble Alps University Grenoble Alpes) and at the Laboratory for Astrophysics, Instrumentation and Modelling (CNRS/CEA/Université Paris Diderot) [3]
when they studied the cluster of progenitor cores W43-MM1 whose structure is more typical of the molecular cloudsof out Galaxy than those observed before. Thanks to the singular sensitivity and resolution of the Alma antenna array in Chili, scientists have determined the distribution of cores which is statistically robust over a heretofore unequalled mass range ranging from solar type stars to stars which are 100 times more massive. With the surprise that this distribution does not satisfy the 1955 relation ! In effect, in the W43-MM1 cloud, the massive cores appear to be overabundant while the less massive ones are underabundant.

These results raise questions concerning the relation between the CMF eand the IMF, and even the universality of the IMF. It is possible that the mass distribution of young stars is not the same everywhere in our galaxy in contrast to what was believed till now. If such is the case, it will be necessary to review the generally accepted law governing stelllar birth and the scientific community will have to review its calculations concerning stellar formation and ultimately all the estimates which depend on the number of massive stars : i.e. the chemical enrichment of the interstellar medium, the number of black holes and of supernovae.

The teams will continue this work with ALMA within the consortium of about forty scientists. Their objective: : study 15 regions similar to W43-MM1 in order to compare their CMF and assess if the characteristics of this cloud can be generalized.

References

The unexpectedly large proportion of high-mass star-forming cores in a Galactic mini-starburst.
F. Motte, T. Nony, F. Louvet, K. A. Marsh, S. Bontemps, A. P. Whitworth, A. Men’shchikov, Q. Nguyen Luong, T. Csengeri, A. J. Maury, A. Gusdorf, E. Chapillon, V. K̈önyves, P.Schilke, A. Duarte-Cabral, P. Didelon and M. Gaudel. Nature Astronomy, le 30 avril 2018. DOI 10.1038/s41550-018-0452-x

[1] For “Initial Mass Function”

[2] For “Core Mass Function”

[3] Scientists from the Observatoire aquitain des sciences de l’univers (CNRS/Bordeaux university), from the Laboratoire d’études du rayonnement et de la matière en astrophysique et a tmosphères(CNRS/Observatoire de Paris/Sorbonne Université) and from the Institute for milllimeter astronomy have collaborated in this work.

Dernière modification le 21 décembre 2021