Home Past Events Archive Colloquium Colloquium: “What We can Learn from Light: Observational Signatures of Rotating Black Holes” — Thursday, February 10, 2022 at 4 PM

Colloquium: “What We can Learn from Light: Observational Signatures of Rotating Black Holes” — Thursday, February 10, 2022 at 4 PM

Delilah Gates, Ph.D.
Associate Research Scholar
Princeton Gravity Initiative
Princeton University
Princeton, NJ
Thursday, February 10, 2022, 4 PM
George P. Williams, Jr. Lecture Hall, (Olin 101)
Video Link will be available if needed
To obtain the video conference link, contact wfuphys@wfu.edu

A reception will be held outside Olin Building Entrance* at 3:30 PM prior to the colloquium. All interested persons are cordially invited to attend.
*Due to Covid restrictions, the university requires all food served and consumed outside. Inclement weather arrangements provided if needed.


As we enter the era of precision black hole imaging, identifying universal observational signatures which of the near horizon strong field region will become increasingly useful in constraining the parameters–mass, spin, spin axis orientations–of the black holes. In this talk we describe progress in analytic characterization of such signatures. These arise from two critical phenomena related to the Kerr geometry: the presence of the photon shell (a region of critical null geodesics), and the emergence of a throat of divergent proper length in the near horizon of near maximally rotating black holes.

We present two such observational signatures for electromagnetic emission:
First, we analytically predict the polarized near-horizon emissions for high-spin black holes like M87* and find a distinctive pattern of whorls aligned with the spin. Next, we analyze the maximum observable blueshift of the electromagnetic emission from an equatorial disk of emitters on stable circular equatorial orbits around a Kerr black hole. We find that small values of the maximum blueshift yield an excellent probe of inclination, while larger values provide strong constraints on spin or inclination in terms of the other.

Reference Materials:

  1. Polarization Whorls from M87* at the Event Horizon Telescope
  2. Maximum Observable Blueshift from Circular Equatorial Kerr Orbiters

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Feb 10 2022


4:00 pm - 6:00 pm


Daniel Kim-Shapiro