CEA-Irfu: An international team led by the Astrophysics Department-AIM Laboratory of CEA-Irfu has just obtained new clues about the origin of the mass distribution of stars, combining observational data from the large interferometer ALMA and the APEX radio telescope operated by the European Southern Observatory (ESO) and the Herschel Space Observatory. Thanks to ALMA, the researchers have discovered in the Cat’s Paw Nebula (NGC 6334), located at about 5,500 light years distant, the presence of protostellar dense cores much more massive than those observed in the solar vicinity. Researchers have shown that there is a close link between the mass distribution of interstellar filaments and the mass distribution of stars. The density – or mass per unit length – of the parent filaments is the crucial parameter that controls the masses of newly-formed stars. This discovery provides a key clue to the origin of stellar masses. These results are published in three articles of the journal Astronomy & Astrophysics.

Stars are major building blocks of the Universe and the life of a star is almost entirely determined by its initial mass. But, the origin of the mass distribution of stars at birth – called the initial mass function by astronomers – is still an unresolved issue. It has long been thought that stars are formed by the collapse of more or less spherical interstellar clouds. But from 2009, the Herschel space observatory, observing in the far infrared and submillimeter, has allowed a fundamental breakthrough by revealing that stars are born mainly in dense filaments of cold gas. When these long filaments of gas, at a temperature of barely ~ 10 K (10 degrees above absolute zero), reach a critical density threshold of approximately 5 solar masses per light-year of length, the mass concentration becomes sufficient to form stars. By observing interstellar clouds in the solar neighborhood, the results of the Herschel satellite have shown that star-forming filaments are all about the same width, close to ~ 0.3 light-years. In these clouds, the characteristic mass of stars formed by fragmentation of filaments is approximately ~ 0.3 solar mass. The ALMA study focused on a massive star-forming region known as NGC 6334, also known as the Cat’s Paw Nebula, located approximately 5500 light years from Earth. This nebula was one of the first regions “photographed” by the ArTéMiS camera observing at the wavelength of 350 μm. The ArTéMiS image revealed that the main filament has a width of about 0.5 light-years, very similar to that measured with Herschel for filaments in the solar neighborhood. The mass per unit length of this filament – about 300 solar masses per light-year – is however more than twenty times higher than the line mass of most of the filaments observed in the solar neighborhood [continues].