Intl research finds clue on spinning of black hole

Observation data from an international research team composed of researchers from 45 institutions around the world has found that the supermassive black hole jet at the center of one of the largest galaxies in the local universe, Messier 87, exhibits periodic oscillations.

The phenomenon is in line with Albert Einstein's general theory of relativity, which predicts that if a black hole is spinning, it will cause the surrounding matter to move along the direction of the black hole spin, an effect known as "frame dragging".

The results of the study, conducted over the past two decades, 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.

A paper about the research was published on the website of the journal Nature on Wednesday.

"This groundbreaking research demonstrates the importance of international collaboration in unlocking the mysteries of the universe. The journey to explore the mysterious supermassive black holes will go on in this way," said Cui Yuzhu, first author and corresponding author of the paper and a postdoctoral researcher from Zhejiang Lab, a new type of research and development institution led by the Zhejiang provincial government, supported by Zhejiang University and Alibaba Group.

The supermassive black holes at the center of an active galaxy are some of the most destructive and mysterious objects in the universe. They have a huge gravitational pull, "swallowing" large amounts of matter through accretion disks, while "spitting" matter thousands of light-years away at close to the speed of light. However, the mechanism of energy transfer between supermassive black holes, accretion disks and jets has remained a puzzle for more than a century.

Scientists widely believed there may be a magnetic field near the black hole and the black hole is likely rotating, which will generate an electric field like a conductor cutting magnetic field lines, thereby accelerating the charged particles around the black hole, and eventually some of the matter will be ejected with huge energy. The spin of supermassive black holes is a key factor in this hypothesis.

The very-long-baseline interferometry network across 45 institutions globally from 2000 to 2022 ultimately found the most direct observational evidence of the spin of black holes so far. In their research, they found that the periodic oscillations are about every 11 years and the amplitude is about 10 degrees.

More than 20 radio telescopes around the world contributed to the research. Two telescopes of the Chinese Academy of Sciences — the 65-meter Tianma Telescope of the Shanghai Astronomical Observatory and the 26-meter Nanshan Radio Telescope of the Xinjiang Astronomical Observatory — have been participating in the observation since 2017, and have played an important role in improving the sensitivity and angular resolution of observations.

Discoveries in recent years have demonstrated the unique advantages of millimeter-wave VLBI technology in exploring the mysteries of the universe, said Shen Zhiqiang, a researcher with the Shanghai Astronomical Observatory.

The Shanghai Astronomical Observatory's Shigatse 40-meter radio telescope, which started construction recently, will enhance high-resolution millimeter-wave imaging observation capabilities. The Qinghai-Tibet Plateau, where it is located, is one of the most suitable sites for millimeter-wave observations in the world, and scientists hope to promote the development of observations in that wavelength, Shen said.