Space area discovered where star formation doesn’t match current models

the W43-MM1 area (Image courtesy ESO/ALMA/F. Motte/T. Nony/F. Louvet/Nature Astronomy. All rights reserved)
the W43-MM1 area (Image courtesy ESO/ALMA/F. Motte/T. Nony/F. Louvet/Nature Astronomy. All rights reserved)

An article published in the journal “Nature Astronomy” describes a research on a region of space about 18,000 light years from the Earth in which a remarkable star formation is being observed, cataloged as W43-MM1. A team of researchers used the ALMA radio telescope to study it and found that more massive stars are forming than predicted by current models.

In past decades, the observation of groups of stellar cores under formation and groups of newborn stars led astronomers to notice that the ratio between the masses of massive objects and the less massive ones remained constant. The conclusion was that what’s called in jargon the initial mass function (IMF) was the result of what’s called in jargon Core Mass Function (CMF), meaning the mass distribution of the cores at the origin of stars.

This empirical law has been confirmed over decades of observations of molecular clouds – the ones from which stars are born – that in astronomical terms are close to the Earth. They are not very dense while in other areas of the Milky Way there are others much denser and now that there are instrumentats that can detect what is inside them we can start understanding if that law still applies.

The star-forming area W43-MM1 has a structure much more typical of molecular clouds existing in the Milky Way than those in which until now it was possible to study the distribution of the masses of the cores of forming stars. For this reason, it was already the subject of some research and some members of the team that carried out this new examination already studied its structure describing it in an article published in the journal “Astronomy & Astrophysics” in October 2014.

This time, the researchers, coordinated by the Grenoble Institute of Planetology and Astrophysics (CNRS/Université Grenoble Alpes) and the Astrophysics, Instrumentation and Modelling Laboratory, (CNRS/CEA/Université Paris Diderot), exploited the power and sensitivity of the ALMA (Atacama Large Millimetre / Submillimetre Array) radio telescope, inaugurated in March 2013. The result is that they established a statistically solid distribution over an unprecedented range of masses, from stars with a Sun-like mass to stars a hundred times more massive.

The analysis of that distribution shows that it doesn’t match that predicted by the empirical law obtained decades ago. In the W43-MM1 area there are more massive cores than expected with a poor representation of less massive cores, the ones that are supposed to be more common as small stars are the most common.

This study represents another step towards a better understanding of star-forming mechanisms within molecular clouds. It involved various international institutions and is one of those that in recent years is studying this problem. For example, an article published in December 2017 in “The Astrophysical Journal” reported a discussion on the influence of the abundance of the various elements present in molecular clouds and the speed of materials in the forming stars.

The W43-MM1 area was very interesting but now the researchers who conducted the study published in “Nature Astronomy” intend to continue using the ALMA radio telescope to examine fifteen similar areas. Their purpose is to compare their CMFs to understand if in that type of cloud there’s also some empirical law that regulates star formation.

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