By Zhao Hanbin, Kunming, March 31st - Researchers from the Yunnan Observatories of the Chinese Academy of Sciences, led by Dr. Li Zhenwei, have proposed a new mechanism for the formation of hot subdwarf stars, providing a theoretical explanation for some observed samples of helium-rich hot subdwarfs. Their findings have been published in the prestigious international astronomical journal "Astrophysics."
Hot subdwarf stars, which are helium-burning stars, are mostly found in binary star systems. They are of great significance in understanding frontier issues in astronomy, such as the evolution of the Milky Way's structure, and are important objects of study in astronomy. Moreover, hot subdwarf binaries with extremely short orbital periods are also important sources of gravitational waves. The gravitational wave radiation signals they produce are expected to be captured by future space-based gravitational wave detectors.
The mainstream research models suggest that stars evolve into red giants, lose their envelopes through interactions in binary systems, and eventually produce hot subdwarf stars, known as the red giant channel. However, this cannot explain the recently observed peculiar hot subdwarf star SMSS J1920. This star is the third hot subdwarf binary discovered to have undergone mass transfer. Approximately 10,000 years ago, it experienced a common envelope ejection process. The typical evolutionary timescale for hot subdwarfs produced by the red giant channel is several tens of millions of years, which is clearly inconsistent with the observational results. To explain the origin of SMSS J1920's evolution, researchers have proposed a new formation channel for hot subdwarf stars, namely the asymptotic giant branch (AGB) channel.
Unlike hot subdwarf stars produced by the red giant channel, those generated under the AGB channel have a carbon-oxygen core, a helium shell, and a hydrogen envelope. Based on relevant numerical calculations, researchers have successfully constructed a model of hot subdwarf stars produced by the AGB channel. This new model can well explain the observational characteristics of SMSS J1920.
This brand-new theory of hot subdwarf star formation provides a new perspective for understanding the evolutionary correlations of different types of hot subdwarf stars.
