Shulou(Shulou.com)11/24 Report--

CTOnews.com, February 6, according to the official website of Yunnan Observatory, recently, Dr. Li Zhenwei, a large sample star evolution research group of Yunnan Observatory, and his collaborators have studied in detail the physical properties of the double white dwarf galaxy in the Milky way by using the latest material exchange stability criterion and combined with the double star family evolution model. The results were published in the journal Astronomy & Astrophysics on January 14.

White dwarf star is an ancient fossil in the universe, which is of great significance to the study of star evolution and star formation history of galaxies. Double white dwarf is a double star system composed of two white dwarfs orbiting each other, which plays an important role in many fields. The merging of double white dwarfs can produce Ia type supernovae as cosmological standard candlelight. Some close double white dwarfs have orbital periods of only a few minutes, which are important target sources for future space gravitational wave detectors. In addition, the formation of double white dwarfs plays an important role in understanding binary evolution, tidal effects, matter transfer, and common envelope evolution.

In the process of formation, double white dwarfs have to go through at least one material exchange between binary stars, and the stability of matter transfer directly determines the final evolution products of binary stars. In the early research, people mostly use the binary matter transfer stability criterion given by the multi-party model. In recent years, GE Hongwei and others have established an adiabatic matter loss model (Ge model) to give a criterion for the stability of matter transfer of stars in different evolution states. Compared with the results given by the multi-party model, the new criterion holds that the mass transfer of stars in the giant star branch tends to be more dynamically stable. Therefore, when the new material transfer stability criterion is adopted, the properties of double white dwarfs will change fundamentally (see figure 1).

Based on the latest material transfer stability criterion, the researchers successfully constructed the double white dwarf star family in the Milky way galaxy. Theoretical calculations show that the Ge model can better reproduce the merging rate distribution of observed double white dwarfs (see left of figure 2) and the merging rate distribution of binary stars with very low mass white dwarfs (see right of figure 2). In addition, they found that the contradiction between the spatial density of double white dwarfs in the early theoretical model and observation can be well solved by using the new material transfer stability criterion. On this basis, the researchers further studied the influence of the merging of double white dwarfs on Ia type supernovae and the gravitational wave radiation properties of double white dwarfs, which provided theoretical support for the corresponding observations. The results show that the influence of matter transfer stability on the double white dwarf star family is decisive. The new material transfer stability criterion can better support the observation constraint.

The research results are supported by the National key Research Program and the National Natural Science Foundation of China.

Figure 1: schematic diagram of the formation of double white dwarfs. MS-main sequence star, AGB-asymptotic giant branch, WD-white dwarf, CE-share a common envelope.

Figure 2: merging rate distribution of double white dwarfs. The merging rates of all double white dwarfs are calculated on the left, and only those containing very low mass white dwarfs (ELM WD) are calculated on the right.

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