Despite recent progress, the question of what controls the star formation efficiency in galaxies remains one of the most debated in astrophysics. According to the dominant view, star formation is controlled by turbulence and feedback, with a star formation efficiency of 1-2% per local free-fall time. In an alternative scenario, the star formation rate in the Galactic disk is proportional to the mass of dense gas above a critical density threshold. In a new study, astrophysicists from Université Paris-Sacra show that Michael Mattern and his colleagues aimed to distinguish between the two images with high-resolution observations. Atacama Pathfinder Experiment (APEX) tracks dense gas and young stars in a comprehensive sample of 49 nearby dense molecular clouds.
This composite image shows RCW 106, a star-forming region in the southern constellation Norma, about 12,000 light-years from Earth. The image overlays a red map of dense gas taken by APEX’s ArTéMiS camera on top of an optical image taken by ESO’s VLT Survey Telescope. Image credit: ESO / M. Mattern others.
Understanding what controls the efficiency of star formation in galactic giant molecular clouds is a fundamental unsolved problem in star formation research.
The star formation rate at multiple scales in galaxies is known to be strongly correlated with the mass of available molecular gas.
Overall, star formation is observed to be a very inefficient process.
“The glowing red clouds seen in the image above indicate regions of dense gas where new stars are being born in the RCW 106 region,” the astronomers said in a statement.
“But only 1 percent of this gas actually forms stars, and we don’t know why this percentage is so low.”
“We know that star formation occurs when regions of these giant clouds of cold gas come together and eventually collapse, and new stars are born. This happens at a critical density.”
“But beyond that density, could even more stars be formed in even denser regions? And could this help explain the 1% mystery?”
Their new results suggest that this is not the case: the dense regions are not efficient for star formation.
According to the team, this can probably be explained by these dense clouds breaking up into filaments and nuclei from which stars form, but many questions remain.
“Our results suggest that the star formation efficiency does not increase as the density passes a critical threshold, supporting a scenario in which the star formation efficiency in dense gas is nearly constant,” the researchers said.
“However, measurements of star formation efficiency tracked by young class I stars in nearby clouds are inconclusive, as they are consistent with both the existence of a density threshold and its dependence on density above the threshold.”
“Overall, we suggest that the efficiency of star formation in dense gas is determined primarily by the physics of filament fragmentation into protostellar cores.”
of study will be displayed in journal Astronomy and Astrophysics.
_____
M. Mattern others2024. Understanding star formation efficiency in dense gas: Initial results from the ArTéMiS CAFFEINE survey. A&Ain press; arXiv: 2405.15713
Source: www.sci.news
