Black holes are famous for hiding secrets. Scientists have discovered a periodic signal originating from what was once a star destroyed by a black hole. The signal repeats itself once every 20 days in the form of pulsations, suggesting that such behaviour of the remnants might represent the clearest evidence for a phenomenon predicted by Albert Einstein a hundred years ago.According to experts, these results paid attention to tidal disruption events, which occur when a star crosses an area near a supermassive black hole and gets shredded by intense gravity. What is left of the destruction creates a bright disk of matter and sometimes even high-powered jets.The specific event, named AT2020afhd, occurred in a galaxy located at a distance of 120 million light-years from Earth. This phenomenon was studied for a while, and scientists recorded the wobbling changes in its luminosity.AT2020afhd points to Einstein’s General Theory of RelativityResearchers explain that this phenomenon is referred to as frame-dragging. It originates from Einstein’s General Theory of Relativity. The concept describes how gravity affects the structure of spacetime.If the massive body in question rotates, it not only bends space-time but also makes certain twists in it as well. According to scientists who study effects such as Lense-Thirring precession, aka frame-dragging, this is like a spinning object dragging the space around it in a piece of fabric.The process of twisting affects nearby matter in a similar way to gravitational forces, although no forces are applied to matter.Frame-dragging was discovered in the debris of a star’s destructionThe twisting of the space-time fabric has been observed in the remnants of the star’s destruction. Namely, a disc of hot, luminous gas was formed around the black hole as a result of a star’s disintegration. At the same time, part of the gas was ejected in a pair of high-speed jets.Physicists noted that both jets and the disc oscillated with respect to each other in a periodic manner. Dr Cosimo Inserra of Cardiff University, who contributed to the research, revealed that this is strong evidence that the disk and jet are physically connected and precessing together. The study highlights that the motion repeated roughly every 20 days, creating a clear and predictable pattern.
Astronomers are excited about this strange 20-day signal from a dead star. Image credit – Gemini
Scientists confirmed the analogy with two telescopesTo verify the signal, the scientists utilised two telescopes – NASA’s Neil Gehrels Swift Observatory and the Karl G. Jansky Very Large Array. These devices detected a common periodicity. The emission of the X-rays increased and decreased in parallel with changes in radio emissions.It is especially significant since the presence of periodicities in the behaviour of two different kinds of light decreases the likelihood of accidental detection. Scientists stated that the detection of signals coincidentally at the same time at different energies further strengthens an astrophysical source for the signal.Significance of the discoveryGravity-induced frame-dragging was examined before, and even a special mission – NASA’s Gravity Probe B mission – was undertaken on Earth. But the gravitational force in this case was substantially lower.In this case, black holes offer an ideal setting for studying the theory in practice, as a black hole is characterised by a strong field. Moreover, there is now a new possibility of exploring black holes because the spin is one of its key parameters.Researchers from the National Astronomical Observatories of the Chinese Academy of Sciences explained that this wobble could serve as a tool to estimate the speed at which the black hole is spinning.By knowing more about spin, scientists might figure out how black holes eject plasma jets and affect their environment.Future implications for space researchThis particular discovery demonstrates that black holes are much more dynamic than previously believed. They’re not just devouring anything within reach. Instead, they’re capable of creating complex patterns of destruction, which help uncover hidden laws of physics.Einstein hypothesised the existence of time and space twisting some 100 years ago. Now, his idea has become a reality for astronomers. Further, missions like the Einstein Probe will detect rapid cosmic events and study them in detail.
