The first black hole humanity has ever imaged has also provided us with what researchers are calling "unequivocal evidence" that black holes spin. An international team of scientists headed by Chinese researcher Dr. Cui Yuzhu analyzed 22 years of observational data gathered by more than 20 telescopes around the world. What they found was that the black hole at the center of galaxy M87, which is 6.5 billion times more massive than our sun, exhibits an oscillating jet that swings up and down every 11 years. This phenomenon confirms that the black hole is indeed spinning.
Black holes gobble up huge amounts of gas and dust, which they attract with their massive gravitational pull. A small fraction of those particles that don't fall into the black hole get spewn out and travel close to the speed of light, showing up as narrow beams along the axis. These beams are called "jets." The telescopes' observations show that M87's jet oscillates by 10 degrees in a recurring 11-year cycle, just as predicted by Einstein's General Theory of Relativity.
So, what causes the M87's jet to swing back and forth? The researchers' analysis indicates that the black hole's spin axis doesn't perfectly align with the rotational axis of its accretion disk. This disk-like structure is typically found surrounding a black hole, because it's made of materials that gradually spiral into the void to be consumed. That misalignment between the rotating mass and the matter that swirls around it causes "a significant impact on surrounding spacetime," which affects the movement of nearby objects in what the General Theory of Relativity calls "frame-dragging."
This is a significant discovery that massively improves our understanding of the mysterious region of spacetime — aside from proving Einstein right, of course. Scientists have yet to find out the size of M87's accretion disk and how fast its black hole is spinning, though, and that entails further observation and analysis.