Chinanews.com, Beijing, February 19 (Reporter Sun Zifa) The latest news from the National Astronomical Observatory of the Chinese Academy of Sciences. The three research teams at home and abroad have separately discovered the first constant star black hole in history-Cygnus X1 (Cygnus X-1). The most accurate measurement and limitation of distance, mass, spin and their evolution were made, and it was found that the X-ray black hole binary star system contains a black hole with a mass of 21 times the sun, and its rotation speed is very close to the speed of light.

　　This is the only X-ray binary system with a black hole that has a mass of more than 20 times the mass of the sun and rotates so fast that scientists have so far discovered and confirmed.

　　In the early morning of February 19, Beijing time, this important astronomical research result independently completed by three teams from Australia, the United States and China was jointly published in three papers in the international scientific journals "Science" and "Astrophysical Journal".

Among them, Zhao Xueshan and Zheng Xueying, a researcher and student of the National Astronomical Observatory of the Chinese Academy of Sciences, are the co-authors of the "Science" paper, and as the first author and corresponding author in the "Astrophysical Journal" a paper on the precise measurement of black hole rotation.

Once made Hawking admit defeat

　　Cygnus X1 is an X-ray binary star system that includes a blue giant star in addition to compact stars that can generate X-ray sources.

　　Since the system was first discovered by an American sounding rocket in 1964, the question of whether the dense object is a black hole or a neutron star has always been a hot spot in the field of high-energy astrophysics research.

　　In the 1970s, physicists Thorne and Hawking made a written bet on this.

It wasn't until the 1990s that more and more observational evidence showed that the center of the system should be a black hole, and Hawking signed his gambling agreement.

　　Accurate measurement "one twists and turns"

　　However, the nature of this black hole binary star system has not been accurately measured before.

In 2011, Gou Lijun and his collaborators made the first precise measurement attempt on the nature of the black hole. The result at that time was that the distance between the black hole system and the earth was 6067 light-years, and the mass was 14.8 times the mass of the sun. The visual interface is rotating at 72% of the speed of light.

　　In 2013, the European Space Agency’s Gaia (GAIA) satellite was launched into space. It plans to accurately measure the distance of 1 billion stars in the Milky Way, including Cygnus X1. The distance of Cygnus X1 is about 7,100 light years. .

　　In the latest paper published in Science, the leading team of Professor Miller-Jones from Curtin University in Australia used the American Very Long Baseline Interferometric Array (VLBA) to measure and confirm the distance of Cygnus X1 again through the triangular parallax method.

After they combined the new observation data with the previous observation data and eliminated the systematic error effect caused by the jet motion of Cygnus X1, they finally got the latest distance of the black hole of Cygnus X1 at 7,240 light-years, with an accuracy of 8%. .

　　On this basis, the cooperative team re-analyzed the optical data and found that the mass of the black hole increased by 50% to 21 times the mass of the sun with an accuracy of 10%.

This has also become the only black hole X-ray binary star system whose main star has a mass over 20 times the mass of the sun in the X-ray binary system.

Accurately limit the rotation speed

　　The rotation of a black hole only affects a range of about a few hundred kilometers close to the visual interface of the black hole. Therefore, its rotation speed needs to be inferred by using the X-ray band data of the higher photon energy generated by the accretion disk located in this area.

　　Gou Lijun’s team combined the newly obtained distance and mass measurement results and analyzed the X-ray spectrum data to achieve precise limits on the black hole’s rotation speed. Compared with the previous measurement results, it was found that the rotation of the Cygnus X1 black hole measured this time was more extreme. The black hole horizon is spinning at least 95% of the speed of light. This is the only known black hole system that rotates at such a high speed.

Compared with gravitational wave detection

　　The complete and high-precision measurement of the system parameters also allows the research team to make a stricter restriction on the evolution of the Cygnus X1 black hole binary system.

A team led by Professor Mandel of Monash University in Australia published a paper on stellar evolution, saying that in order to form a black hole with such a weight and rotating extremely fast, the stellar wind loss should be several times smaller than previously estimated, and the predecessor of the black hole weighs 60 times. Solar mass.

　　Researcher Gou Lijun said that precise measurement of system parameters also provides scientists with an opportunity to compare with black holes detected by gravitational waves.

The rotation of Cygnus X1 is extremely fast, and it exhibits completely different rotation characteristics from the black hole system discovered by gravitational waves. This also means that the X-ray binary system is likely to have a completely different formation mechanism from the gravitational wave system.

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