Researchers have made new progress in the field of accretion white dwarfs

Recently, Cui Yingsheng and Meng Xiangcun, phD students at the Yunnan Astronomical Observatory of the Chinese Academy of Sciences, have made new progress in the field of accretion of white dwarfs. They found that the accretion of material in white dwarfs can effectively prevent the occurrence of optical thick stellar winds on the surface of white dwarfs, which may change people’s understanding of the model of the single-simple star of the predecessor of type Ia supernova. The International Scientific Journal, THE ROYAL ASTRONOMICAL SOCIETY MONTHLY (MNRAS), RECENTLY PUBLISHED THE RESULTS ONLINE UNDER THE TITLE “The viability of the optically thick wind model in accreting WDs at high accretion rates”.

In the 1990s, people used type Ia supernova ranging to find that the universe was expanding at an accelerating rate, meaning that there was dark energy in the universe, a discovery that posed a huge challenge to basic physics research. Although Type Ia supernovae are so important in modern cosmology and even in fundamental physics, it is not clear how Type Ia supernovae came about (the problem of type Ia supernova precursors). If the problem of type Ia supernova precursor stars is not solved, it may hinder the development of precise cosmology. Accretion white dwarfs are considered one of the most likely progenitor candidates for Type Ia supernovae, a binary system consisting of a white dwarf and a normal star. However, there is still a lot of controversy about how accretion white dwarfs evolve into Type Ia supernovae. Previous research has found that if the rate of material transfer between binary stars is too high, the white dwarf will soon merge with the companion star into a single star, so that there will be no Type Ia supernova explosion. To overcome this difficulty, an optical thick stellar wind model was proposed, that is, an optical thick stellar wind generated on the surface of a white dwarf to adjust the rate of material transfer between binary stars to avoid merger between white dwarfs and companion stars. Therefore, the optical thick stellar wind model is considered to be the physical basis for the white dwarf to be able to explode through accretion material type Ia supernovae.

In recent years, however, many observations have been found to contradict the predictions of the optical thick stellar wind model, meaning that optical thick stellar winds may not have occurred in the predecessor stars of type Ia supernovae. To this end, the researchers reconsidered the conditions under which optical thick stellar winds occur, proposing that the interaction between the accretion of material and stellar winds in white dwarfs can prevent the occurrence of optical thick stellar winds. The study found that the ability to occur optical thick starwinds strongly depends on the magnitude of the rate of material transfer between binary stars. At a sufficiently high rate of material transfer, the accretion of material by white dwarfs can effectively block the formation of optical thick stellar winds (see Figure 1). This result provides a theoretical explanation for resolving the contradiction between the optical thick stellar wind model and observation, and also raises new questions about the study of the predecessor star of the Type Ia supernova.

Figure 1. Velocity profile evolves over time when the material transfer rate exceeds the critical accretion rate, where the black line is the outline of the local escape velocity. As can be seen from the figure, although the movement speed of the internal material can exceed the escape speed from the ground, due to the continuous obstruction of the accretion material, the cladding as a whole is still in a confined state, and no optical thick star wind occurs

The research results have been funded by the Western Light Cross Team of the Chinese Academy of Sciences and the National Natural Science Foundation of China. (Source: Yunnan Astronomical Observatory, Chinese Academy of Sciences)

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