Medeiros et al. / Event Horizon Telescope Collaboration
Black hole in the galaxy M87
A team of astrophysicists, led by researchers at the Institute for Advanced Study, has developed an innovative technique for searching for light echoes from black holes.
Their new method, which will make it easier to measure the mass and rotation of black holes, represents a major step forward, as it works independently of many of the other ways scientists have probed these parameters in the past.
The investigation, in the magazine The Astrophysical Journal Lettersintroduces a method that could provide direct evidence that photons circulate around black holess due to an effect known as “gravitational lens“.
A gravitational lens occurs when light passes close to a black hole and its trajectory is distorted by the strong gravitational field of the black hole.
The effect allows light to follow multiple paths from a source to an observer on Earth: some light rays may follow a direct route, while others may circle the black hole once – or several times – before reaching us. This means that light from the same source can arrive at different times, resulting in an “echo”.
“The fact that light circulates around black holes, causing echoes, is a theory that has existed for years, but these echoes have not yet been measured,” says the study’s lead author, George N. Wongmember of the Institute’s School of Natural Sciences and researcher at Princeton University.
“Our method provides a blueprint for making these measurements, which could revolutionize our understanding of black hole physics,” he adds.
Technique allows you to fail echo signatures are isolated from the strongest direct light captured by well-known interferometric telescopes, such as the EHT (Event Horizon Telescope).
Both Wong and one of her co-authors, Lia Medeirosprofessor in the Institute’s School of Natural Sciences and NASA Einstein Fellow at Princeton University, have worked extensively as part of the EHT Collaboration.
To test their technique, Wong and Medeiros, together with James Stonefrom the School of Natural Sciences, and Alejandro Cárdenas-Avendañofrom Los Alamos National Laboratory and formerly associated with Princeton University, performed high-resolution simulations that took tens of thousands of “snapshots” of light traveling around a supermassive black hole similar to the one found at the center of the galaxy M87 (M87*), which is located about 55 million light years from Earth.
Using these simulations, the team demonstrated that their method could directly infer the echo delay period in the simulated data. They believe that their technique will be applicable to other black holes, in addition to M87*.
“This method will not only be able to confirm when the light orbiting a black hole has been measured, but will also provide a new tool to measure the fundamental properties of the black hole”, explains Medeiros.
Understanding these properties is important. “Black holes play a significant role in the evolution of the Universe,” says Wong.
“While we often focus on how black holes pull things in, they also expel large amounts of energy into their environment,” adds the researcher.
“Black holes play an important role in the development of galaxies, affecting how, when and where stars form and helping to determine how the structure of the galaxy itself evolves“, Salienta Wong.
“Know the distribution of mass and rotation of black holes, and the shape how this distribution changes over timegreatly improves our understanding of the Universe”, concludes the astronomer.
Measuring the mass or spin of a black hole is complicated. The nature of the accretion disk, namely the spinning structure of hot gas and other matter that spirals inward toward a black hole, can “confuse” the measurementobserva Wong.
However, light echoes provide a mass independent measurement and rotation, and the existence of multiple measurements allows us to produce an estimate for these parameters “that we can really believe in”, says Medeiros.
Detecting light echoes could also allow scientists to better test Albert Einstein’s theories of gravity.
Using this technique, we can find things that make us think “Hey, this is weird!“, says Lia Medeiros. “The analysis of this data can help us verify whether black holes are in fact consistent with general relativity”, highlights the Brazilian astophysicist.
The team’s results suggest that it may be possible to detect echoes with a pair of telescopes – one on Earth and one in space – working together to perform what can be described as “long baseline interferometry”.
Such an interferometric mission only needs to be “modest,” says Wong. Their technique provides a practical and viable method for collecting important and reliable information about black holes.
