A group of scientists has presented the first conclusive evidence that black holes can indeed rotate, shedding light on one of the most mysterious and disruptive phenomena in our universe.
Simulation image of beams emitted from a black hole. Image: Handout
According to the Morning Post, after over two decades of sifting through observational data from the global network of radio telescopes, the research team discovered that the supermassive black hole in the M87 galaxy emitted rotating beams akin to a spinning top.
The research findings, published in the journal Nature, revealed that it took approximately 11 years for these beams to complete one cycle. Notably, astronomer Gou Lijun at the National Astronomical Observatory of China, who was not involved in the study, commented, “This is the first observational evidence showing that black holes not only spin but also precess. This discovery has been made possible through extensive data accumulation and meticulous observational analysis, emphasizing the significance of collaboration between astronomers and the utilization of astronomical instruments in advancing our understanding of the universe.”
As per Gou, the precession motion of a spinning top typically comprises two parts: the spin motion of the top itself and the continuous change in the direction of the axis of rotation around a central point. This process is known as precession.
For instance, the Earth rotates every 24 hours to create a day and night cycle. In contrast, the Earth completes a precession cycle over approximately 26,000 years. Currently, the Earth’s axis is tilted about 23 degrees relative to its orbit around the Sun.
Scientists harnessed a hot gas swirl around black holes to study their rotation. Gou noted that most black holes spin at incredibly high speeds, with some approaching the speed of light.
In 2019, humanity had the first opportunity to capture a direct image of the supermassive black hole in the M87 galaxy, which is approximately 55 million light-years away from Earth and weighs 6.5 billion times the mass of the Sun.
Analyzing the details of the M87 black hole, researcher Cui Yuzhu from the Zhejiang Provincial Key Laboratory of Quantum Control and Applied Quantum Technology and her colleagues observed that the black hole’s beams, formed by particles ejected from its poles, appeared to be oriented differently in 2017 compared to previous observations.
According to Cui, subsequent to this discovery, researchers synthesized data collected between 2000 and 2022 from 20 radio telescopes located in China, Japan, South Korea, Italy, and Russia. The analysis results showed that these beams exhibited periodic motion, with a regular cycle of approximately 11 years and an inclination angle of about 10 degrees.
To understand what caused the precession cycle of these beams, the research team conducted theoretical analysis and numerical simulations with the assistance of supercomputers at the National Astronomical Observatory of Japan. They found that because the actual spin axis of the black hole does not align perfectly with the rotation axis of the surrounding accretion disk, this axial misalignment caused the beams to exhibit wobbling motion. This phenomenon had also been predicted in Albert Einstein’s theory of general relativity.
“This precession discovery provides clear evidence that the supermassive black hole in M87 is indeed spinning,” the researchers wrote.
However, scientists still need to determine the speed of rotation of the M87 black hole and leverage these profound insights to elucidate the formation processes of supermassive black holes. This has been a long-standing question in the field.