A cataclysmic stellar event observed in 2024 has furnished cosmologists with their most definitive substantiation to date of a black hole distorting the very fabric of spacetime in its vicinity.
This phenomenon, referred to as frame-dragging or the Lense-Thirring effect, was witnessed at the nucleus of a galaxy designated LEDA 145386, situated approximately 400 million light-years from our planet. This observation has afforded researchers an unparalleled chance to witness the principles of general relativity manifesting in real-time.
“This discovery represents a significant boon for theoretical physicists, as it corroborates predictions formulated well over a century ago,” states astrophysicist Cosimo Inserra, affiliated with Cardiff University in the United Kingdom. “Furthermore, these observations contribute invaluable insights into the nature of tidal disruption events – precisely when a celestial body is obliterated by the prodigious gravitational forces emanating from a black hole.”
Frame-dragging is a theoretical consequence of general relativity, and its conceptualization can be grasped through an analogy. Envision immersing a utensil into viscous fluid and imparting rotational motion to it. The fluid will subsequently orbit the utensil, with the rotational effect diminishing in intensity as the distance from the utensil increases.
Any entity possessing mass induces a curvature in spacetime. When such a mass is in rotation, the resultant deformation of spacetime exhibits a corresponding helical distortion. Prior instances of observing frame-dragging have been documented, including its influence on orbital dynamics of artificial satellites in Earth’s orbit.
However, in Earth’s proximity, this effect is remarkably subtle. Frame-dragging becomes substantially more pronounced in the vicinity of celestial objects possessing masses several million times that of our Sun, such as supermassive black holes, thereby transforming these environments into ideal settings for scrutinizing the intricate workings of this phenomenon.
Naturally, a primary challenge is that supermassive black holes are typically situated at distances too vast to permit detailed investigation of their more nuanced activities. Consequently, we are frequently compelled to await infrequent cataclysmic occurrences, such as the disintegration of a star, to precisely quantify any elusive behaviors.
This scenario aligns with the circumstances surrounding the black hole at the core of LEDA 145386, which boasts a mass approximately five million times that of the Sun.
In January of 2024, the Zwicky Transient Facility registered a pronounced increase in the object’s luminosity, a characteristic that scientific analysis identified as consistent with a tidal disruption event – the luminous outpouring accompanying the violent fragmentation of a star by the black hole’s formidable gravitational field. While such occurrences are known, they are infrequent and exceptionally intriguing, prompting astronomers to maintain continuous observation.
“Upon a star’s close approach to a supermassive black hole, the black hole’s intense gravitational pull stretches the star and ultimately tears it asunder, initiating the accretion of stellar material onto the black hole,” elucidates astronomer Santiago del Palacio of Chalmers University in Sweden.
“Such an event results in an immense surge of brightness; the discovery of a new instance prompted us to promptly commence observations of the black hole across multiple electromagnetic spectrum bands.”
Over a period, an anomalous pattern began to manifest. At precise intervals of 19.6 days, the X-ray emissions originating from the black hole underwent fluctuations in intensity exceeding an order of magnitude. Concurrently, the radio emissions emanating from the object also exhibited variability, with a disparity surpassing four orders of magnitude. Significantly, these fluctuations in both X-ray and radio wavelengths were synchronized.
The process of a black hole consuming a star is termed a tidal disruption event, attributable to the star’s disintegration under the influence of the black hole’s tidal forces – its differential gravitational pull. During this event, the stellar remnants do not instantaneously cross the black hole’s event horizon; instead, its dismembered constituents are ejected and coalesce into an accretion disk encircling the black hole, progressively spiraling towards its event horizon.
Not all of the stellar material is consumed. Current astrophysical models propose that a portion of this material is propelled along magnetic field lines towards the black hole’s polar regions, from which it is expelled into interstellar space with extraordinary velocity, generating colossal jets of matter traveling at speeds approaching the speed of light.
The accretion disk surrounding the black hole is the source of X-ray radiation, while the synchrotron acceleration of the jet produces radio emissions. The synchronized variations observed in both phenomena indicate that the entire structure is oscillating like a spinning top – a manifestation of frame-dragging.
“Such cross-band, high-amplitude, and quasi-periodic synchronous variability strongly implies a rigid coupling between the accretion disk and the outflowing jet, which precesses in a gyroscopic manner around the black hole’s rotational axis,” explains co-first author Yanan Wang of the Chinese Academy of Sciences.
Computational models simulating a co-oscillating disk and jet yielded comparable outcomes, thereby substantiating the proposition that celestial bodies like LEDA 145386’s turbulent black hole serve as invaluable observational arenas not only for the study of accretion dynamics and jet formation but also for empirically validating the tenets of general relativity.
“By demonstrating that a black hole possesses the capacity to warp spacetime and induce this frame-dragging effect, we are also commencing to apprehend the underlying physical mechanisms of this process,” observes Inserra.
“In essence, much like an electrically charged entity generates a magnetic flux field when it rotates, we are observing how a massive, spinning object – in this specific instance, a black hole – generates a gravitomagnetic field that exerts an influence on the trajectories of stars and other cosmic bodies in its vicinity.”
