Twisted light, a new tool for General Relativity and beyond

TL;DR

This paper presents the first observational evidence that light near a rotating black hole carries orbital angular momentum, enabling direct measurement of black hole spin and testing of General Relativity.

Contribution

It introduces the use of twisted light as a novel observational tool for measuring black hole spin and probing fundamental physics.

Findings

First observational evidence of twisted light near a black hole

Direct measurement of black hole spin parameter

Potential to test General Relativity with black hole probes

Abstract

We describe and present the first observational evidence that light propagating near a rotating black hole is twisted in phase and carries orbital angular momentum. The novel use of this physical observable as an additional tool for the previously known techniques of gravitational lensing allows us to directly measure, for the first time, the spin parameter of a black hole. With the additional information encoded in the orbital angular momentum, not only can we reveal the actual rotation of the compact object, but we can also use rotating black holes as probes to test General Relativity.