Study of 39 interstellar clouds challenges conventional model of high-mass star formation

Astronomers have successfully mapped out 39 interstellar clouds where the formation of high-mass stars is expected to occur. This extensive dataset has challenged the prevailing model of low-mass star formation, indicating that the process of forming high-mass stars is fundamentally distinct, rather than merely a matter of scale.

The formation of high-mass stars is of great significance in the evolution of the universe, as they contribute to the release of heavy elements and generate powerful shockwaves through supernova explosions. Despite their importance, the mechanisms underlying the formation of massive stars remain poorly understood due to their rarity.

In order to shed light on this elusive process, a team led by Kaho Morii, Patricio Sanhueza, and Fumitaka Nakamura employed the Atacama Large Millimeter/submillimeter Array (ALMA) to observe 39 infrared dark clouds (IRDCs). These IRDCs are immense, frigid, and dense aggregations of gas and dust, which are believed to serve as the birthplaces of massive stars. The researchers specifically focused on clouds that exhibited no signs of ongoing star formation, aiming to investigate the early stages preceding the ignition of young stars. Within these 39 clouds, the team discovered over 800 potential stellar seeds, known as molecular cloud cores, which are anticipated to develop into stars.

The findings from their study were published in a research article titled “The ALMA Survey of 70μm Dark High-mass Clumps in Early Stages (ASHES). IX. Physical Properties and Spatial Distribution of Cores in IRDCs” in The Astrophysical Journal on June 20, 2023.

Remarkably, it was determined that 99% of these cores lack the necessary mass to give rise to high-mass stars, assuming that high-mass stars follow the same evolutionary trajectory as the more comprehensively studied low-mass stars. These results lend support to the notion that the formation mechanism for high-mass stars must differ from that of their low-mass counterparts.

Additionally, the team investigated the distribution patterns of these cores. In stellar clusters, high-mass stars tend to be clustered together, while low-mass stars exhibit a more dispersed distribution. However, this investigation unveiled that the locations of higher-mass cores show no preference when compared to the positions of lower-mass cores. Conversely, denser cores displayed a tendency to be localized and concentrated. This implies that denser cores, rather than those with greater mass, might serve as the progenitors of high-mass stars. It also suggests that denser cores may experience more efficient growth compared to less-dense cores.

Source: National Astronomical Observatory of Japan

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