ALMA reveals three star-forming cores at different stages inside one gas clump

Astronomers have discovered three dense cores at various evolutionary stages within a massive star-forming region called G40.282−0.219, using data from the Atacama Large Millimeter/submillimeter Array (ALMA). Previously, low-resolution observations were unable to distinguish individual dense cores or determine their properties and stages of evolution. However, a new study has identified three such cores within G40.282−0.219 and analyzed their physicochemical characteristics and evolutionary states.

The study, led by doctoral student A. G. Tegegne at the Xinjiang Astronomical Observatory of the Chinese Academy of Sciences, examined the cores using ALMA data in the 1.3 mm band. The researchers found that the most massive core, MM1, has the smallest number of detected molecular spectral lines and lacks associated outflows or masers, indicating it is the youngest core.

In contrast, MM2, the second core, is the most evolved, with a powerful outflow and a silicon monoxide (SiO) jet moving at nearly 25 km/s. MM3, the smallest core, is the hottest and has the richest variety of molecules, hosting a Class II methanol maser.

The findings suggest that an evolutionary sequence exists within the massive young stellar object cluster G40.282−0.219, with MM1 being the youngest and MM3 the most evolved. The researchers emphasize that to accurately determine the evolutionary stages of dense cores in massive star-forming regions, it is crucial to consider multiple factors, including mass, density, temperature, outflows and jets, the richness of molecular spectral lines, and the types of detected masers. The study was published in The Astrophysical Journal.