Hawking lost the first stellar black hole in its history to be accurately measured

Our reporter Lu Chengkuan

Is Cygnus X1 a black hole? Hawking once said, it’s not! To this end, he also bet with people.

On February 19, three articles published online in science and Acta astrophysics jointly released the latest accurate measurements of Cygnus x1, the first stellar black hole discovered in history. Three teams from Australia, the United States and China independently measured and limited the distance, mass, rotation and evolution of black hole Cygnus x1. They found that this system contains a black hole with 21 times the mass of the sun, and its rotation speed is extremely fast, close to the speed of light. This is the only X-ray binary system with a black hole mass more than 20 times the mass of the sun and rotating so fast.

Cygnus X1 is an X-ray binary system, which contains not only compact stars that can produce X-ray sources, but also a blue giant. “Since this system was first discovered by the American sounding rocket in 1964, whether the compact object is a black hole or a neutron star has been a hot topic in the field of high energy astrophysics.” Gou Lijun, a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, said.

In the 1970s, physicists Thorne and Hawking made special bets on whether compact objects are black holes or neutron stars. It was not until the 1990s, when more and more observational evidence showed that the center of the system should be a black hole, that Hawking signed to admit defeat.

Although Hawking has given up, there has been a lack of accurate measurement of the nature of the system. In 2011, researcher Gou Lijun and his collaborators made the first attempt to accurately measure the nature of the black hole. The result is: the distance between the black hole system and the earth is 6067 light years, the mass is 14.8 times the mass of the sun, and it is found that the visual interface of the black hole is rotating at 72% of the speed of light.

In 2013, the European aviation agency’s Gaia satellite was launched, planning to accurately measure the distance of 1 billion stars in the galaxy, including X-ray binaries such as Cygnus x1. As a result, Gaia’s distance of Cygnus X1 is a little further than before, about 7100 light-years.

The research team led by Professor Miller Jones of Curtin University, Australia, used the very long baseline interferometric array of the United States to measure and confirm the distance of Cygnus X1 again by using the trigonometric parallax method. After combining the new observation data with the previous observation data, and eliminating the systematic error effect caused by the jet motion of Cygnus x1, the team finally obtained the latest distance of Cygnus x1 Black hole, which is 7240 light-years, with an accuracy of 8%, which is completely consistent with the distance given by Gaia satellite.

On this basis, the team reanalyzed 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 is the only black hole X-ray binary star system with a mass of more than 20 times the mass of the sun.

Combined with the new distance and mass measurement results, the research team led by Chinese astronomers analyzed the X-ray spectral data, thus accurately limiting the rotation speed of the black hole. Compared with the previous measurement results, it was found that the rotation of the black hole in this measurement is more extreme, and the black hole visual interface is rotating at least 95% of the speed of light, which is the only one known so far Black hole system with high speed rotation.

The complete and high-precision measurement of system parameters enables researchers to make a more stringent restriction on the evolution process of the system. According to Professor Mandel of Monash University in Australia, to form a black hole with such weight and extremely fast rotation, the stellar wind loss should be several times smaller than previously expected, and the predecessor of the black hole may weigh 60 times the mass of the sun.

Accurate measurement of the system parameters also gives us an opportunity to compare with the black holes detected by gravitational waves, Gou said. The rotation of Cygnus X1 is very fast, which is completely different from that of the black hole system discovered by gravitational waves. It also means that this system may have a completely different formation mechanism from the gravitational wave system.