5.2 Holograms and Symmetry Review

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Further analysis of the Event Horizon Telescope's image of black hole M87 could reveal emergent conformal symmetries. In 2021, it was discovered that the light ring around the black hole's shadow consists of polarized photons, indicating the presence of powerful magnetic fields.

The horizon of a black hole is a peculiar region of spacetime.

It turns out that black holes can spin, and there is a maximal amount at which they can spin, as the horizon cannot exceed the speed of light:$$J=GM^2$$
These extreme Kerr black holes, which are spinning as fast as the Einstein equations will allow, turn out to be very simple objects.
The event horizon of an extreme Kerr black hole is a very special and peculiar region of spacetime, with some unusual, perhaps holographic properties.

New symmetries have emerged.

Recently, the quantum version of the Einstein equations has implied an infinite number of emergent symmetries near the horizon. Such emergent symmetries, known as conformal symmetries, are familiar in condensed matter physics (such as with the quantum Hall effect), but new to astrophysics.
These symmetries suggest that the horizon of some black holes plays the role of a holographic information storage plate. We do not understand the general case, but it is a good start.
These conformal symmetries were the key feature of analyzing black holes in string theory. In other words, beginning with string theory, these symmetries were deduced, which enabled physicists to understand more how black holes can store information.
Now that these symmetries have been discovered, string theory isn’t necessary in the description anymore.

We are on the precipice of being able to measure incredible new data.

The Event Horizon Telescope could, for the first time, put conformal symmetry on firmer footing. Coordinated radio telescopes around the world will examine two black holes, Sagittarius A* and M-87 (the ones that appear largest in our sky), and might be able to see the region where conformal symmetry appears.
According to Professor Strominger, the beauty of physics is in the amazing ability of mathematics to describe the world in precise, measurable and coherent detail.