The “Black Hole Hunter” used the Guo Shoujing telescope to discover the Ning static neutron star

On September 23, the reporter learned from the National Astronomical Observatory of the Chinese Academy of Sciences that based on the time domain survey data of the Guo Shoujing Telescope (LAMOST), a major national scientific and technological infrastructure, the research team of the LAMOST Black Hole Hunter Program found a static neutron star about 1037 light-years from the Earth in a binary star system. The relevant research results were published in Nature – Astronomy.

Fig. 1 An art of the binary system of neutron stars, with neutron stars in blue and red being its companion red dwarf (pictured: Yu Jingchuan).jpg

An art of this neutron binary system, with neutron stars in blue and red as its companion red dwarf (Drawn: Yu Jingchuan)

Neutron stars are massive stars that evolve to the end of life, after a violent supernova explosion, the formation of extremely dense objects in the center, it together with white dwarfs and black holes, it becomes the last three final products of the evolution of stars of different masses.

In 1967, scientists discovered the first pulsar, which was subsequently confirmed as a fast autobiographical neutron star, a discovery that transformed the neutron star from a theoretical conjecture into a real object that could be actually observed.

Liu Jifeng, co-corresponding author of the paper and researcher of the National Astronomical Observatory of the Chinese Academy of Sciences, introduced that in general, there are three ways to search for neutron stars: to capture neutron stars by searching for pulse signals generated by high-speed rotating neutron stars; Neutron stars are found by observing the gaseous material of the compact accretion companion star in the binary star system to form an accretion disk and emit bright X-rays; Or discover neutron stars by detecting gravitational waves emitted by the merger of binary neutron stars.

But there are some static neutron stars and static black holes that can neither detect pulse signals nor emit X-rays, and how to find a suitable way to discover these tranquil neutron stars or black holes is the key for astronomers to study the family of compact objects and their physical properties.

When the research team used LAMOST time-domain survey data to conduct a search program for compact objects such as black holes and neutron stars, they discovered a special binary star system with a different spectrum from a single star through a radial velocity monitoring method. The binary star system consists of a red dwarf with 0.6 solar masses and an invisible object that has not been detected by a telescope, and this invisible object is most likely a compact star.

Then, the research team used the 5-meter Haile telescope of the Palomar Observatory in the United States for follow-up observations, and combined with the high-precision photometric observations of the Transit Exoplanet Survey Satellite (TESS) in the United States, further analysis and measurement, and believed that the dense object of the binary star system was a neutron star with about 1.2 solar masses.

“The visible red dwarf in binary systems orbits about every 6.6 hours under the gravitational pull of neutron stars. Interestingly, the neutron star is not accumulating material on its companion star, so it is impossible to detect bright X-rays and is currently a neutron star that is still static. Liu Jifeng said.

Subsequently, the research team used China’s 500-meter aperture spherical radio telescope (FAST) to conduct radio observations of the neutron star for one hour, and also did not observe the pulse signal of the neutron star. This indicates that the neutron star’s pulse signal is absent or very faint to detect, or it may be that the pulsed radiation is not pointing to Earth.

In addition, the research team learned from multi-band observations that the red dwarf sphere in the binary system is more active. Due to the strong tidal forces of neutron stars , the red dwarf star as its companion star is stretched and deformed into a teardrop shape. The system is like a shining “ruby” silently around the quiet neutron star, and the beautiful double star dance is staged in interstellar space a thousand light years away.

This discovery is also another important achievement achieved by the team in the field of hunting compact objects with the advantage of LAMOST sky survey, following the identification of a statically static stellar black hole using the apparent velocity monitoring method in 2019.

Liu Jifeng said that LAMOST’s world-leading spectral acquisition rate and the absolute advantage of large-scale sky survey allow astronomers to use the apparent velocity monitoring method to discover compact objects such as tranquil black holes and neutron stars, breaking the observation restrictions of relying on detecting pulse signals, X-rays, etc. to search for compact objects, which opens up a new way for the discovery of compact objects in the static binary star system.

“Using this method, the research team is expected to discover more dense objects such as neutron stars and black holes, and construct a statistically significant distribution of the mass of dense objects, thus unraveling the mystery of a series of basic problems in the study of compact objects.” Liu Jifeng said. (Source: China Science Daily, Gao Gaoli)

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