The cosmos has presented an extraordinary opportunity for a group of scientists, revealing one of the most elusive phenomena in the night sky. Their study, published today in Science Advances, details the first observations of a swirling vortex in spacetime caused by a rapidly rotating black hole.
This phenomenon, known as Lense-Thirring precession or frame-dragging, describes how black holes twist the spacetime around them, affecting nearby objects like stars and causing their orbits to wobble. The team, led by the National Astronomical Observatories at the Chinese Academy of Sciences and supported by Cardiff University, focused on AT2020afhd, a tidal disruption event (TDE) where a star was torn apart by a supermassive black hole.
Unveiling the Cosmic Dance
A swirling disk formed around the black hole from the remnants of the star, ejecting powerful jets of matter at nearly the speed of light. Through rhythmic changes in both X-ray and radio signals from the event, the team observed the disk and the jet wobbling in unison, repeating every 20 days. This observation confirms a prediction of general relativity first theorized by Einstein in 1913 and mathematically defined by Lense and Thirring in 1918.
“Our study shows the most compelling evidence yet of Lense-Thirring precession – a black hole dragging spacetime along with it much like a spinning top might drag water around it in a whirlpool,” said Dr. Cosimo Inserra, a Reader in the School of Physics and Astronomy at Cardiff University and one of the paper’s co-authors.
Theoretical Predictions Meet Observational Evidence
The confirmation of this phenomenon offers scientists new avenues for studying black hole spin, accretion physics, and jet formation. Dr. Inserra emphasized the significance of these findings, noting that they not only confirm century-old predictions but also enhance understanding of TDEs, where stars are shredded by a black hole’s immense gravitational forces.
Unlike previous TDEs studied, which exhibited steady radio signals, AT2020afhd showed short-term changes, unaccounted for by energy release from the black hole and its surrounding components. This further confirmed the dragging effect, providing scientists with a novel method for probing black holes.
Unlocking the Mechanics of Frame-Dragging
The team modeled X-ray data from the Neil Gehrels Swift Observatory (Swift) and radio signal data from the Karl G. Jansky Very Large Array (VLA) to identify the frame-dragging effect. Further analysis using electromagnetic spectroscopy allowed them to describe and identify the process.
“By showing that a black hole can drag spacetime and create this frame-dragging effect, we are also beginning to understand the mechanics of the process,” explained 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.”
Implications and Future Exploration
This discovery not only confirms theoretical predictions but also opens new pathways for understanding the universe’s most mysterious objects. As Dr. Inserra eloquently put it, “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 flavors that nature has produced.”
The paper, titled ‘Detection of disk–jet coprecession in a tidal disruption event,’ is now available in Science Advances, marking a significant milestone in astrophysical research and offering fresh insights into the enigmatic nature of black holes.
