Holography of the photon ring

Shahar Hadar, Daniel Kapec, Alexandru Lupsasca, Andrew Strominger

Research output: Contribution to journalArticlepeer-review


Space-based next-generation interferometers propose to measure the Lyapunov exponents of the nearly bound geodesics that comprise the photon ring surrounding the black hole M87*. We argue that these classical Lyapunov exponents equal the quantum Ruelle resonances describing the late-time approach to thermal equilibrium of the quantum microstate holographically dual to any Kerr black hole such as M87*. Moreover, we identify ‘near-ring regions’ in the phase space of fields propagating on Kerr that exhibit critical behavior, including emergent conformal symmetries. These are analogues for sub-extremal Kerr of the much-studied ‘near-horizon regions’ of (near-)extremal black holes. The emergent conformal symmetries greatly constrain the observational predictions for the fine photon ring substructure around M87* and for quasinormal gravitational-wave ringdowns, as well as any proposal for a quantum holographic dual to the Kerr black hole. More generally, we hope that our identification of several universal features of Kerr spectroscopy provides a useful starting point for a bottom-up approach to holography for astrophysical black holes.

Original languageEnglish
Article number215001
JournalClassical and Quantum Gravity
Issue number21
StatePublished - 3 Nov 2022

Bibliographical note

Publisher Copyright:
© 2022 IOP Publishing Ltd.


  • black hole
  • holography
  • photon ring

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


Dive into the research topics of 'Holography of the photon ring'. Together they form a unique fingerprint.

Cite this