The team, led by researchers at the National Astronomical Observatories of the Chinese Academy of Sciences with support from Cardiff University, studied AT2020afhd, a tidal disruption event in which a star was torn apart by the intense gravity of a supermassive black hole. As the star was destroyed, its debris formed an accretion disk around the black hole, and jets of matter were launched at close to the speed of light.
By tracking regular changes in both X-ray emission and radio signals from AT2020afhd, the researchers found that the disk and jet were wobbling together with a period of about 20 days. This synchronized wobble is interpreted as evidence of Lense-Thirring precession, also known as frame dragging, in which a spinning black hole twists the surrounding spacetime and alters the orientation of nearby orbits.
Lense-Thirring precession was first anticipated in 1913 in work associated with Einstein's ideas and then formally described by physicists Josef Lense and Hans Thirring in 1918, making this detection a direct test of a prediction of general relativity. The new result provides a way to probe black hole spin, the behavior of matter in accretion disks, and the mechanisms that generate relativistic jets.
Dr Cosimo Inserra, a Reader in the School of Physics and Astronomy at Cardiff University and a co-author of the study, said: "Our study shows the most compelling evidence yet of Lense-Thirring precession - a black hole dragging space time along with it in much the same way that a spinning top might drag the water around it in a whirlpool. "This is a real gift for physicists as we confirm predictions made more than a century ago. Not only that, but these observations also tell us more about the nature of TDEs - when a star is shredded by the immense gravitational forces exerted by a black hole.
"Unlike previous TDEs studied, which have steady radio signals, the signal for AT2020afhd showed short-term changes, which we were unable to attribute to the energy release from the black hole and its surrounding components. This is further confirmed the dragging effect in our minds and offers scientists a new method for probing black holes."
To identify the frame-dragging effect, the researchers modeled X-ray data from NASA's Neil Gehrels Swift Observatory and radio data from the Karl G. Jansky Very Large Array. They also analyzed the composition, structure, and properties of the material around the black hole using electromagnetic spectroscopy, which helped them characterize the precessing disk and jet.
"By showing that a black hole can drag space time and create this frame-dragging effect, we are also beginning to understand the mechanics of the process," explains Dr Inserra. "So, in the same way a charged object creates a magnetic field when it rotates, we're seeing how a massive spinning object - in this case a black hole - generates a gravitomagnetic field that influences the motion of stars and other cosmic objects nearby.
"It's a reminder to us, especially during the festive season as we gaze up at the night sky in wonder, that we have within our grasp the opportunity to identify ever more extraordinary objects in all the variations and flavours that nature has produced."
Research Report:Detection of disk-jet co-precession in a tidal disruption event
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Cardiff University
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