Observational signature of high spin at the Event Horizon Telescope

Samuel E. Gralla, Alexandru Lupsasca, Andrew Strominger

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


We analytically compute the observational appearance of an isotropically emitting point source on a circular, equatorial orbit near the horizon of a rapidly spinning black hole. The primary image moves on a vertical line segment, in contrast to the primarily horizontal motion of the spinless case. Secondary images, also on the vertical line, display a rich caustic structure. If detected, this unique signature could serve as a 'smoking gun' for a high spin black hole in nature.

Original languageEnglish (US)
Pages (from-to)3829-3853
Number of pages25
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Apr 2018


  • Black hole physics
  • Gravitational lensing: strong

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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