Black hole spin finally finds more powerful observational evidence! On September 27, Beijing time, the top international journal Nature published a paper on black hole research led by Chinese scientists, finding that the black hole jet at the center of the M87 galaxy shows periodic swings, with a swing period of about 11 years and an amplitude of about 10 degrees.
The results of this study successfully linked the dynamics of the black hole jet at the center of the M87 galaxy with the state of the supermassive black hole at the center of the galaxy, providing observational evidence for the existence of the spin of the M87 black hole. This is another major achievement in the field of black hole research after the first black hole "doughnut" photo in 2019 and the release of the black hole panoramic photo in April this year.
According to reports, an international scientific research team composed of 79 researchers from 45 research institutions in 10 countries around the world analyzed the observation data of multiple "Very Long Baseline Interferometry" (VLBI) networks from 2000 to 2022. The results of this observational data analysis of 170 datasets, which spanned 23 years, confirmed the prediction in Einstein's general theory of relativity that "if the black hole is spinning, there will be a drag effect".
Whether black holes spin has been a focus of the scientific community
Supermassive black holes active at the center of galaxies are among the most destructive and mysterious objects in the universe. They have a huge gravitational pull, "eating" large amounts of matter through accretion disks, while also "spitting" matter thousands of light-years away at high speeds close to the speed of light. However, what is the mechanism of energy transfer between supermassive black holes, accretion disks and jets? It's a puzzle that has puzzled physicists and astronomers for more than a century.
At present, scientists widely accepted the theory that the angular momentum of the black hole is the source of energy, and one possibility is that if there is a magnetic field near the black hole and the black hole is in a rotating state, it will produce an electric field like a conductor cutting magnetic field lines, thereby accelerating the ionization around the black hole, and eventually some of the matter will be ejected with huge energy. Among them, the spin of supermassive black holes is a key factor in this theory. However, the spin parameters of black holes are extremely difficult to measure, and there is no direct observational evidence even whether the black hole is in a rotating state.
Dr. Kazuhiro Qin of the National Astronomical Observatory of Japan said: "Following the use of the Event Horizon Telescope to take pictures of the black hole in the galaxy M87, whether this black hole is spinning has always been the core concern of scientists. ”
To study this challenging question, researchers studied the supermassive black hole at the center of galaxy M87 and its jets. The galaxy M87 is a neighboring galaxy 55 million light-years from Earth with a black hole at its center with a mass 6.5 billion times greater than the Sun, and astronomers first observed the jet in M87 in the optical band in 1918, which was also the first cosmic jet observed by humans. These features make the M87 galaxy the best target for astronomers to study the relationship between black holes and jets, and astronomers can use VLBI technology with ultra-high angular resolution to resolve jet structures very close to black holes.
Scientists around the world have joined forces to unravel the gluttonous black hole spin phenomenon
Cui Yuzhu, the first author and corresponding author of this research paper and a postdoctoral researcher at Zhijiang Laboratory, began to contact the Event Horizon Telescope project in 2017 during his doctoral studies. When the first EAVN observations were processed in 2017, the jet structure of M87 showed a different pointing angle than previously recognized. Through careful comparison, she found that the jet of the M87 black hole is not constant in only one direction, and the data of observations in different years show that the direction of the jet is different and seems to have a certain regularity. What causes the direction of the jet to be deflected? Since then, Cui Yuzhu began to lead a long-term monitoring project for the jet angle of the M87 black hole.
This long-term monitoring project is observed by the East Asian VLBI network jointly by China, Japan and South Korea, and many domestic units have started in-depth cooperation. Since 2017, the 65-meter Tianma Telescope of the Shanghai Astronomical Observatory of the Chinese Academy of Sciences and the 26-meter Radio Telescope of Nanshan of the Xinjiang Astronomical Observatory have continuously participated in the observation of the East Asian VLBI Network (EAVN), respectively, and have played an important role in improving the sensitivity and angular resolution of observations.
The work used 170 observations from multiple international observing networks, including the East Asia VLBI Network (EAVN), the Very Long Baseline Array (VLBA) in the United States, the KVN in Korea and the VERA Joint Array (KaVA) in Japan, and the EATING Observing Network from East Asia to Italy/Russia, and more than 20 radio telescopes worldwide contributed to the study. By analyzing VLBI observations over the past 23 years, the researchers successfully captured the periodic precession of the jet in M87.
What forces in the universe can regularly change the direction of this huge jet of energy? After a lot of analysis, the research team reasoned that the answer to the question may lie in the dynamic properties of the accretion disk: matter with a certain angular momentum will orbit the black hole and form an accretion disk, and they will continue to approach the black hole by the gravitational pull of the black hole until they are irreversibly "sucked" into the black hole. However, the angular momentum of the accretion disk can be affected by a variety of random factors, and it is very likely that there is a certain angle with the spin axis of the black hole. But the black hole's super-strong gravity can have a significant impact on the surrounding space-time, causing nearby objects to be dragged along the direction of the black hole's rotation, which in turn triggers periodic precession of accretion disks and jets.
The research team conducted a large number of detailed theoretical investigations and analyses based on observations, and used supercomputers to carry out the latest numerical simulations combining the properties of M87. The numerical simulation results confirm that when there is an angle between the rotation axis of the accretion disk and the spin axis of the black hole, the entire accretion disk will be precessiond due to the drag effect of the reference frame, and the jet will also produce precession under the influence of the accretion disk. Detecting the precession of the jet can provide strong observational evidence for the spin of the black hole at the center of M87, and bring new insights into the nature of supermassive black holes.
Cui Yuzhu said: "We are very happy and lucky to have this important discovery. Due to the small angle between the black hole's spin axis and the accretion disk angular momentum, and the precession period for more than ten years, the accumulation of high-resolution data of more than two cycles and the careful analysis of the structure of M87 are necessary conditions for obtaining this result. ”
Dr. Qin Hehong said: "Now, our results further confirm the previous expectations from observations, and this gluttonous black hole is indeed spinning. ”
In the course of the project, Lin Weikang, associate researcher of the Southwest China Institute of Astronomy of Yunnan University, Yangsuke Mizuno, associate professor of the Li Zhengdao Research Institute of Shanghai Jiao Tong University, Dr. Yu Jintao of the Air Force Early Warning College of the People's Liberation Army Chinese People's Liberation Army, Jiang Wu, associate researcher of Shanghai Astronomical Observatory, Chinese Academy of Sciences, and Cui Lang, researcher of Xinjiang Astronomical Observatory, made important contributions to data analysis and theoretical model comparison and interpretation.
The journey of space exploration will continue
Based on this work, the team predicts that there are more black holes at the center of galaxies with similarly skewed accretion disk structures, but how to detect more sources with tilted disks also presents greater challenges. There are still many mysteries that require more long-term observations and more detailed analysis. Shen Zhiqiang, a researcher at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, emphasized, "Scientific discoveries in recent years have fully demonstrated the unique advantages of millimeter-wave VLBI technology in studying supermassive black holes and exploring the mysteries of the universe."
The recently started construction of the Shanghai Astronomical Observatory's Shigatse 40-meter radio telescope will further enhance EAVN's high-resolution millimeter-wave imaging observation capabilities. In particular, the Qinghai-Tibet Plateau is one of the most suitable sites for (sub)millimeter wave observations in the world, and scientists hope to promote the development of submillimeter wave astronomical observations in China. ”
"The universe has never been silent, and with the development of modern astronomy, especially radio astronomy, we have captured huge and rich cosmic signals through radio telescopes. Radio telescopes and mobile phones receive signals based on the same basic principle, and both need to be sampled at high speed in the time domain to generate massive amounts of data. Further integration of the rapidly developing frontiers of computational science and radio astronomy exploration will reveal the nature of the mysterious phenomena of the universe, including black holes. Li Jing, researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, chief scientist of "China Sky Eye" and chief scientist of computational astronomy at Zhijiang Laboratory, said.
With the continuous accumulation of data, Zhejiang Laboratory is introducing artificial intelligence, cloud computing and other technologies into astronomical research, improving data processing efficiency and expanding the space for exploring physical parameters.
This groundbreaking research demonstrates the importance of international collaboration in unlocking the mysteries of the universe. Cui Yuzhu said that this research provides a new theoretical model direction for the study of black hole theory, and theoretical physicists may be able to further develop black hole theory. Scientific research is to move forward in the process of putting forward conjectures or theories, looking for experimental data verification, and model correction, and getting closer to scientific truth step by step.
How fast is the spin of the M87 black hole? Observations show that accretion disks are relatively small, why is this? Do other galaxies have similar jet precessions? These mysteries are waiting to be further explored by scientists, and the journey to uncover more mysteries of the universe continues.
Source | People's Daily client
Responsible Editor | Liang Zeming
Editor: Liang Zeming
Source: People's Daily client