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

According to the website of the Chinese Academy of Sciences, Peking University and the National Astronomical Observatory of the Chinese Academy of Sciences, recently using LAMOST spectral data combined with the photometric data of the Nanshan Optical Telescope of Xinjiang Observatory, a binary system consisting of a compact star with a mass of about 0.98 times the solar mass and a late main sequence star has been discovered.

The left picture of ▲ shows the multi-band light variation curve of the system and the results of model fitting, and the picture on the right shows the change of Ha emission lines with orbital period in the optical companion star reference frame. Source: the study combined with multi-band (radio, optical, X-ray and gamma-ray) observation and analysis on the website of the Chinese Academy of Sciences speculates that the compact star may be an "X-ray dim isolated neutron star" (XDINS). This is the first time such an object has been found in a binary system. CTOnews.com learned from the website of the Chinese Academy of Sciences that the relevant research results were published in the Astrophysical Journal KuaiBao.

If all possible energy sources of a neutron star are exhausted, then the star can only radiate the remaining thermal energy. such neutron stars are called X-ray faint isolated neutron stars (XDINS). The thermal spectrum of XDINS is mainly soft X-ray, accompanied by ultraviolet radiation, which shows a quiet state of radio, so it is difficult to find them. According to the theory, it is impossible to produce neutron stars less than 1.17x solar mass through nuclear collapse supernova explosions. The new findings mean that such neutron stars may be produced in other formation channels, such as accretion-induced collapse (AIC) of white dwarfs. In addition, according to the parallax of the Gaia satellite, the binary system, which contains neutron candidates, is only about 385 light-years away. This is the nearest neutron star candidate found so far. The study suggests that heavy elements detected from the Earth's deep sea may be associated with such supernova explosions.

So far, only seven isolated neutron stars with weak X-rays have been found (nicknamed "Seven Musketeers"). They are all relatively close to Earth (about 391light-years to 1630 light-years) and have a rotation period of about 5 to 10 seconds. The newly discovered X-ray faint solitary neutron star is the first of its kind to be found in a binary system.

The discovery is based on the medium and low resolution spectral time domain survey data of LAMOST, combined with the multi-band photometric data of Nanshan Optical Telescope, the photometric data of the exoplanet Survey Satellite (TESS) and the optical survey data of other bands to determine the radius and temperature of the late main sequence stars. By fitting the light variation curve, it is found that the mass of the compact star and the optical companion star in this binary system is about 0.98 times the solar mass and 0.62 times the solar mass, respectively.

Based on the medium resolution spectral data of LAMOST, it is found that the Ha emission line of the system has a bimodal structure. Among them, the relatively wide Ha emission line originates from the stellar chromosphere activity, while the other relatively narrow Ha emission line shows a change in phase with the dense star, so the narrower component may come from the accretion disk. In addition, in more than ten years of sky survey photometric data, the source does not show a large magnitude change, and the X-ray luminosity is low, indicating that the compact star is unlikely to be a white dwarf star, but may be a neutron star.

No high-energy counterpart has been found from the American Fermi satellite. Based on the extremely low X-ray luminosity and relatively soft X-ray spectrum of the system, it can be inferred that the compact star is a XDINS in the binary system. According to the ultraviolet observation of the Galaxy Evolution probe (GALEX) in the United States, the radiation radius of the accretion disk and the death line of the neutron star are obtained. it is known that the rotation period of the neutron star is about 0.52s to 6.5s, which is consistent with the rotation period of XDINS.

The discovery of this "X-ray faint isolated neutron star" candidate, currently closest to Earth and in the binary system, has important scientific significance for analyzing the physical properties, formation and evolution of such special celestial bodies, the researchers said.

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