The first-ever image of a black hole taken by the Event Horizon Telescope captured the imagination of the world earlier this year. The image quickly became the most shared picture on social media and will be, without doubt, the picture that encapsulates 2019 for many people.
What the black hole image that became so-famous this year actually captured was a bright circle of light avoiding the event horizon of the supermassive black hole at the centre of galaxy Messier 87 — this circle is known as an Einstein ring.
Einstein rings are described by the theory of general relativity as the fabric of space-time becoming so distorted by the mass of the gravitational singularity at the centre of the black hole that it acts as a huge lens.
Such rings are simply another example of so-called gravitational lens effects when the distortion of space-time causes the deflection of light. The effect is also seen when the light from distant galaxies is ‘bent’ by a massive object — usually another galaxy — directly in front of it.
The image may well have been a triumph for science, but there are still a multitude of questions left to be answered about these space-time events.
(Left) Image of the black hole in M87 (Right) Image of the AdS black hole constructed from the response function. (©Hashimoto, K., Kinoshita, S., Murata, K., “Einstein Rings in Holography”, Phys. Rev. Lett. 123, 031602, DOI: 10.1103/PhysRevLett.123.031602)
Researchers from Osaka, Nihon, and Chuo Universities have suggested a novel approach to answering said questions. The theoretical framework they put forward involves an experiment to simulate a holographic image of a black hole. Described as a table-top experiment by the researchers, the method they propose could be conducted in labs across the world.
The ultimate aim is to use these simulations to better understand the physics of black holes and bridge the gap between quantum mechanics and general relativity by putting forward a working quantum theory of gravity. One of the consequences would be the accurate calculation of the radius of the Einstein ring.==============
Measuring String theory
As the theory of general relativity best describes the physics of massive objects such as stars and planets and quantum mechanics is used to describe subatomic physics, scientists have long suspected that as black holes consist of a huge mass compressed into an infinitesimally small space the key to unifying these theories lies in their study.
One such theory posits that all matter is composed of vibrating strings, smaller than any known or theorised particle. This theory — unsurprisingly referred to as string theory — also suggests there should be a correspondence between the four dimensions we perceive and strings in space with an additional dimension.
This relationship is often referred to as “holographic duality” as it resembles a 2D holographic surface holding the information of a 3D image or object.
Koji Hashimoto, the lead author of the paper from Osaka University, says: “The holographic image of a simulated black hole if observed by this tabletop experiment, may serve as an entrance to the world of quantum gravity.”
Taking the concept of holographic duality, the team’s study shows how the surface of a sphere — possessing two-dimensions — can be used to model a black hole in three dimensions. Light emitted by a source at one point on the sphere is measured at another showing the black hole if the spherical material allows holography.
The researchers also predict that the radius of the Einstein ring would be obtained should their theory be correct.
Co-author Keiju Murata concludes: “Our hope is that this project shows the way forward towards a better understanding of how our Universe truly operates on a fundamental level.”