Astronomers report strong evidence that a spinning supermassive black hole is dragging spacetime as it consumes a star in tidal disruption event AT2020afhd. Combined X-ray data from the Neil Gehrels Swift Observatory and radio data from the VLA revealed synchronized oscillations in emission repeating on a ~20-day cycle, consistent with Lense-Thirring precession. Modelling shows the accretion disk and jet are precessing together, offering a new way to probe black hole spin, accretion physics, and jet formation.
Einstein Right Again: Spinning Supermassive Black Hole 'Drags' Spacetime While Devouring a Star
An illustration showing the accretion disc surrounding a black hole, in which the inner region of the disc wobbles. | Credit: NASA
A team of astronomers has captured compelling evidence that a rapidly spinning supermassive black hole is literally dragging the fabric of spacetime as it tears a star apart and consumes its material. The observations, centered on the tidal disruption event (TDE) AT2020afhd, are consistent with Lense-Thirring precession — a century-old prediction of general relativity in which a rotating mass pulls nearby spacetime along with it.
How the Signal Was Detected
The researchers combined X-ray measurements from NASA's Neil Gehrels Swift Observatory with radio observations from the Karl G. Jansky Very Large Array (VLA). Instead of the steady radio emission seen in many previously observed TDEs, AT2020afhd displayed synchronized, rhythmic changes in both its X-ray and radio output. These oscillations repeated on a roughly 20-Earth-day cycle, indicating that the accretion disk and the jet were wobbling together.
What Is Happening Around the Black Hole?
In a TDE, a star that ventures too close to a supermassive black hole is stretched and compressed by extreme tidal forces — a process often nicknamed 'spaghettification.' The disrupted stellar material forms streams that settle into a flattened accretion disk. Magnetic fields can channel some of this inflowing matter into twin, near-light-speed jets launched from the black hole's poles.
Because the bright X-ray and radio emission comes from regions just outside the event horizon, any frame-dragging of spacetime by the black hole should imprint a periodic modulation on the observed signals. The team’s modelling shows that the observed ~20-day wobble matches expectations for Lense-Thirring precession produced by a rapidly spinning supermassive black hole.
“Our study shows the most compelling evidence yet of Lense-Thirring precession — a black hole dragging spacetime along with it,” said Cosimo Inserra of Cardiff University. “This is a real gift for physicists as we confirm predictions made more than a century ago.”
Why This Matters
Detecting frame-dragging around a black hole provides a new observational handle on black hole spin, a key parameter that strongly influences how black holes accrete matter and launch jets. Understanding spin and precession also helps explain how jets are oriented and how energy is transported away from the black hole during energetic events like TDEs.
The analysis published in Science Advances on Dec. 10 suggests that careful, multiwavelength monitoring of future TDEs can reveal the dynamics of spacetime close to black holes and shed light on the interplay between accretion disks, magnetic fields, and relativistic jets.
Publication: The research was published Dec. 10 in Science Advances.
