LAMOST discovers largest stellar black hole to date: Mass far exceeds theoretical upper limit

BEIJING, Nov. 28, 2019 (Xinhua) — The international scientific journal Nature today published a major finding by Liu Jifeng and Zhang Wei’s research team at the National Observatory of the Chinese Academy of Sciences. Relying on China’s self-developed national major science and technology infrastructure, the Guo Shoujing Telescope (LAMOST), the research team discovered one of the largest stellar-level black holes to date, and provided a new way to use LAMOST’s advantages to find black holes.

LAMOST discovers largest stellar black hole to date: Mass far exceeds theoretical upper limit

Picture: LB-1’s artistic imagination map Yu Jingchuan

The 70-fold solar-mass black hole is well above the upper limit of the theoretical prediction, upsetting perceptions of star-level black hole formation and promising to revolutionize the theory of stellar evolution and black hole formation.

A black hole is a mysterious object that does not glow in itself. No matter, including light, can escape from it. Depending on mass, black holes are generally divided into star-level black holes, medium-mass black holes and supermassive black holes. Among them, star-level black holes are formed by the death of large-mass stars and are the “inhabitants” of the universe. The theory predicts that there are hundreds of millions of star-level black holes in the Milky Way, but so far astronomers have found only about 20 star-level black holes in the Milky Way — all of which are identified by X-rays from the gas of the black hole’s accretion companion star, all of which are less than 20 times the mass of the sun.

Finding new methods and finding a large number of black holes without X-ray radiation has become a hot and difficult topic in astronomy in recent years.

Beginning in the fall of 2016, a team led by the National Observatory used LAMOST to conduct a two-star study that monitored more than 3,000 stars in a small solar region over a two-year period. It was found that in an X-ray-radiated, tranquil binary system (LB-1), a blue star with an eight-fold solar mass orbited an “invisible object” in a periodic motion. Unusual spectral features suggest that the “invisible object” is most likely a black hole. The researchers then “confirmed”: They further confirmed the spectral properties of LB-1 through the Spanish 10.4-meter Canary Large Telescope and the U.S. 10-meter Keck Telescope, calculating that the black hole was about 70 times the mass of the sun. It’s worth noting that over a two-year period of monitoring, LAMOST made 26 observations for the study, with a cumulative exposure time of about 40 hours. Mr Liu said it would take 40 years to find such a black hole using an ordinary four-meter telescope , which would reflect THE high observational efficiency of LAMOST .

LAMOST discovers largest stellar black hole to date: Mass far exceeds theoretical upper limit

Figure 2 Mass Distribution of Black Holes Found by The Gravitational Wave Convergence Event and X-ray Method

Current stellar evolution theory predicts that black holes up to 25 times the mass of the sun can be formed at the sun’s metallic abundance. The mass of the newly discovered black hole has entered the “no-go zone” of existing stellar evolution theory. The U.S. Laser Interference Gravitational Wave Observatory (LIGO) has discovered black holes of dozens of times the mass of the sun by detecting gravitational waves since 2015, and in 2017, Rene Weiss, Kip Thorne and Barry Barish were awarded the Nobel Prize in Physics for their contributions to LIGO’s construction and gravitational wave detection. “The discovery of a 70-fold solar-mass black hole in the Milky Way will force astronomers to rewrite models of star-level black holes,” commented DAVID REITZ, director of LIGO. This extraordinary achievement, together with the convergence of double black holes detected by the U.S. Laser Interferometry Gravitational Wave Observatory (LIGO) and the European Virgo Observatory over the past four years, will help revive the astrophysical research of black holes.” Next, using LAMOST’s extremely efficient observational efficiency, astronomers are expected to discover a large number of “hidden” black holes, ushering in a new era of mass discovery of black holes.

The work was based on observations from LAMOST (China Xinglong), the Canary Large Telescope (Canary Islands, Spain), the Keck Telescope (Hawaii, United States) and the Chandra X-ray Observatory (United States). The study included 55 authors from 28 countries in China, the United States, Spain, Australia, Italy, Poland and the Netherlands.

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