Research on the Origin of Massive Stars and Related Discoveries
TapTechNews August 3rd news, the origin of massive stars (greater than 8 times the mass of the sun) is a key unresolved problem in the field of astrophysics. The Purple Mountain Observatory, using high-resolution millimeter/submillimeter interferometric array (ALMA) data, reported the currently only massive protostar M17MIR with repetitive explosive accretion and the intermittent high-speed molecular outflows caused by repetitive explosive accretion.
The Chinese Academy of Sciences stated that this research has further deepened scientists' understanding of the origin of massive stars. The relevant research results have been published in The Astrophysical Journal Letters (TapTechNews attaches DOI: 10.3847/2041-8213/ad55c7).
At present, there are relatively few samples of massive protostars showing explosive accretion, including S255IRNIRS3, NGC6334IMM1, G358.93-0.03MM1, and M17MIR, among which M17MIR was first independently discovered by the Purple Mountain Observatory based on long-term infrared data.
Mid-infrared photometric data from 1993 to 2019 found that M17MIR has obvious mid-infrared luminosity variation. The mid-infrared light curve indicates the existence of two obvious infrared luminosity burst periods and a period of quiescence between them. In addition, M17MIR shows a 22 GHz water maser light variation activity almost synchronous with the infrared light variation. Therefore, M17MIR is the first massive protostar with repetitive explosive accretion.
Through spectral energy distribution fitting, the accretion rate of matter during the burst period is estimated to be one-thousandth of the mass of the sun per year. Through repetitive explosive accretion, M17MIR is expected to become an O9-type star with 20 solar masses.
The water maser activity of M17MIR indicates the possibility of the existence of an outflow activity. Through the analysis of ALMA 1.3 millimeter band archived data, it was found that there is a significant excess in the high-speed line wing part of the 12CO (J=2-1) spectral line, and after mapping, intermittent bipolar molecular outflows were found. The extremely high-speed (EHV) part of the outflow shows a symmetrical and collimated jet-like structure, and distinct fine knot-like structures can be resolved. Assuming that the nearest EHV structure N1-1/S1-1 originated from the explosive accretion activity that started in 2010, then the jet speed can be inferred to be about 421 km/s.
Based on this jet speed, it is found that the dynamic age of the EHV structure N1-2/S1-2 exactly corresponds to the explosive accretion activity that occurred in the 1990s, which verifies the rationality and accuracy of the dynamic age. The dynamic ages of the remaining intermittent high-speed molecular outflows are less than 400 years, suggesting that there have been multiple explosive accretion activities in the past 400 years, and each duration is about several decades, which is in line with the gravitational instability and fragmentation model of the gas accretion disk, which has reference value for the theoretical study of the origin of massive stars.