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Illustration showing the accretion disk around a black hole, in which the inner region of the disk oscillates. | Credit: NASA
Astronomers have observed a star orbiting a ravenous supermassive black hole that is tearing it apart and feasting on its stellar material. The observation is evidence of a rare and elusive phenomenon called “lens-thirring precession” or “frame dragging,” in which a rapidly rotating black hole pulls the very fabric of space and time along with its motion.
This twist space time Appeared from the first Albert EinsteinThe 1915 doctrine of General relativitywho predicted that objects with mass form the fabric of space and time (combined as a single entity called spacetime) and that gravity arises from this geometric effect. The greater the mass of an object, the greater its effect on spacetime and thus the greater its gravitational effect. In 1918, Austrian physicists Joseph Lens and Hans Thiering used general relativity to solidify the concept of large, rotating objects pulling spacetime together.
Since then, however, this effect has been difficult for scientists to observe, meaning the new research could provide scientists with a new way to study spin. Black holesIn which they feed, or “accrete,” tidal disruption events (TDE) from stars, and how TDEs give rise to powerful outflows, or jets.
“Our study shows the most compelling evidence to date of Lense-Thirring precession – a black hole dragging spacetime in the same way that a spinning top can eddy water around itself,” team member Cosimo Insera of Cardiff University in the UK said in a statement. “This is a real gift for physicists as we confirm predictions made more than a century ago. Not only that, but these observations tell us more about the nature of TDEs – when a star is torn apart by the immense gravitational force exerted by a black hole.”
See the mess
The team uses NASA spacecraft, the Neil Gehrels Swift Observatory (SWIFT), and the Earth-based Carl G. Jansky began investigating lens-thirring precession by studying TDE designated AT2020afhd using X-ray data collected by radio-wave observations from the Very Large Array (VLA).
A TDE occurs when a star orbits very close to a supermassive black hole, and the massive gravitational influence of the cosmic titan, which can be as large as billions of suns, generates tidal forces within the star that squeeze it horizontally while pulling it vertically. This process, known as spaghettification, creates a strand of stellar pasta that curls around the black hole like a noodle around a fork, called an accretion disk.
Material from the accretion disk is slowly fed into the black hole, but these galaxy-dominating titans are notoriously messy eaters, with some material channeled from the black hole’s pole by powerful magnetic fields. From there, the material explodes as a twin near-light-speed jet of plasma.
The accretion disks of these TDE-accumulated black holes and the jets they erupt radiate brightly in the electromagnetic spectrum, and since these emissions originate immediately outside the black hole, they must be affected by lensing-Thirring precession. This effect translates into a “double” in the orbit of matter in the accretion disk around the supermassive black hole. In fact, while observing AT2020afhd, the team saw rhythmic changes in the X-rays and radio waves coming from this TDE that indicated that the accretion disk and jet were repeating each day.
“Unlike previously studied TDEs, which have steady radio signals, AT2020afhd’s signal showed short-term fluctuations, which we could not attribute to energy release from the black hole and its surrounding components,” Insera continued. “This further confirms the drag effect in our minds and provides scientists with a new method to probe black holes.”
Modeling data from Swift and the VLA, the team was able to confirm that these differences were the result of frame-dragging. Further analysis of these results may help scientists better understand the physics behind the lens-Thirring effect.
“By showing that black holes can drag spacetime and create this frame-dragging effect, we’re also beginning to understand the mechanics of the process,” Incera said. “So, just as a charged object creates a magnetic field when it spins, we’re looking at how a large rotating object—in this case a black hole—generates a gravitational magnetic field that affects the motions of stars and other cosmic objects.
“It is a reminder to us, especially during the festive season when we gaze with wonder at the night sky, that we have the opportunity to recognize even more extraordinary objects in all the variety and flavors that nature has produced.”
The team’s research was published in the journal Wednesday (December 10). Science advances.
