Astrophysicists have developed a method for detecting echoes of light from black holes using gravitational repulsion that will allow measuring their mass and rotation
A group of astrophysicists led by researchers from the Institute for Advanced Study in New Jersey has developed a new technique for detecting echoes of light around black holes. This method enables an innovative way to measure the mass and rotation of black holes, and is an important breakthrough because it works independently of previous measurement techniques.
The research presents an approach that could directly capture photons orbiting black holes through a phenomenon called "gravitational entanglement," which occurs when light passes close to a black hole and its strong gravitational field distorts it. This curvature causes light to travel in several paths from the same source to an observer on Earth. Some of the light rays will travel directly, but others will circle the black hole one or more times before reaching us. As a result, light from the same source can arrive at different times, creating what is known as an "echo".
"The theory that light travels around black holes and creates echoes has existed for years, but such echoes have not been measured until now," says lead author of the study George N. Wong of Princeton. "Our method offers a plan for making these measurements, which may revolutionize our understanding of the physics of black holes."
The technique makes it possible to isolate the weak echo signatures from the stronger direct light captured by famous interferometric telescopes such as the Event Horizon Telescope. Wong and one of the co-authors, Leah Medeiros, worked intensively as part of the Event Horizon Telescope collaboration.
To test their technique, Wong, Medeiros and their colleagues ran high-resolution simulations that took tens of thousands of images of light moving around a supermassive black hole similar to the one at the center of the galaxy M87 (M87*), about 55 million light-years from Earth. Using these simulations, the team showed that their method was able to infer the delay time of the echoes in the simulation data. They believe their technique is applicable to other black holes in addition to M87*.
"This method will not only make it possible to verify when light surrounding a black hole is measured, but will also provide a new tool for measuring the fundamental properties of the black hole," Medeiros explains.
It is important to understand these features. "Black holes play a significant role in shaping the evolution of the universe," says Wong. "We often focus on how black holes pull things in, but they also emit large amounts of energy into their surroundings. "They play an important role in the evolution of galaxies, influencing the manner, timing and location of star formation and helping to determine how the structure of the galaxy itself evolved. Knowing the distribution of the masses and spins of black holes and how the distribution has changed over time greatly improves his understanding of the universe."
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