Measurement of the spin of the M87 black hole from its observed twisted light (1904.07923v4)

Abstract: We present the first observational evidence that light propagating near a rotating black hole is twisted in phase and carries orbital angular momentum (OAM). This physical observable allows a direct measurement of the rotation of the black hole. We extracted the OAM spectra from the radio intensity data collected by the Event Horizon Telescope from around the black hole M87* by using wavefront reconstruction and phase recovery techniques and from the visibility amplitude and phase maps. This method is robust and complementary to black-hole shadow circularity analyses. It shows that the M87* rotates clockwise with an estimated rotation parameter $a=0.90\pm0.05$ with $\sim 95\%$ confidence level (c.l.) and inclination $i=17^\circ \pm2^\circ$, equivalent to a magnetic arrested disk with inclination $i=163^\circ\pm2^\circ$. From our analysis we conclude, within a 6 $\sigma$ c.l., that the M87* is rotating.

• The paper demonstrates a novel method using twisted light's orbital angular momentum to accurately measure the M87* black hole spin (a=0.90 ± 0.05).
• It employs advanced wavefront reconstruction of EHT data to extract OAM spectra, providing precise insights into the rotation and inclination (i=17° ± 2°) of M87*.
• The research opens new pathways for integrating OAM-based analyses with traditional techniques to refine black hole models and deepen our understanding of gravitational effects.

Measurement of the Spin of the M87 Black Hole from Its Observed Twisted Light

The paper by F. Tamburini et al. presents a novel approach for measuring the spin of the supermassive black hole M87*, leveraging the twisted nature of light propagating near such an astrophysical object. This paper provides the first empirical observation of electromagnetic waves carrying orbital angular momentum (OAM), extending our toolkit for astrophysical measurements by a significant dimension.

Methodology and Observations

The research capitalizes on data from the Event Horizon Telescope (EHT), renowned for its role in imaging black hole environments. The technique employed involves extracting OAM spectra from radio intensity data using advanced wavefront reconstruction and phase recovery methods. The presence of specific OAM modes in light emitted in the vicinity of a rotating black hole serves as a direct measure of its rotational characteristics, offering an alternative to conventional analyses focusing on black-hole shadow circularity.

The results indicate the M87* exhibits a clockwise rotation with a spin parameter $a = 0.90 \pm 0.05$, determined with a confidence level of 95%. This finding is consistent across multiple observation epochs analyzed. Additionally, the inclination of the black hole is measured at $i=17^\circ \pm 2^\circ$, aligning with scenarios suggested by magnetic arrested disk models. The inclination and rotation parameter estimates highlight the potential of integrating OAM-based methods into existing astrophysical observatory frameworks.

Implications and Future Prospects

This paper underscores the influence of general relativity and Kerr spacetime on the behavior of light. The ability to detect OAM in black hole environments opens up new observational dimensions for studying such phenomena. By analyzing the distribution and asymmetry of OAM modes, researchers can deduce critical spin and inclination parameters with notable accuracy.

Practically, the work presents an opportunity to refine black hole models and introduces a technique that may complement shadow-based analyses. When combined with other interferometric data or incorporated into multi-wavelength studies, OAM measurement could enhance the fidelity of black hole metrics, potentially offering a more granular understanding of their behaviors and interactions.

Theoretically, the implications bolster our grasp of the interplay between light and curved spacetime, further validating elements of gravitational lensing and vorticity as predicted by general relativity. The detection of OAM modes also points towards a meaningful extension in the paper of electromagnetic wavefronts, allowing for more detailed exploration of astrophysical processes.

Looking forward, the authors suggest innovations in telescope technology that may capitalize on these findings. Enhancements could include better fidelity in capturing phase information and intermediate OAM states, or developing detection apparatus specifically tuned to these observables. Such advancements would likely enable more precise measurements of black hole properties and instigate broader applications within observational cosmology.

In conclusion, this breakthrough represents a noteworthy step in black hole research, utilizing a novel approach that complements and extends traditional methodologies, and invites new possibilities for both observational and theoretical astrophysics.