CAREER: Exploring the Photon Ring and Broadening Participation in Relativity via Interactive Black Hole Visualizations

Vanderbilt University, Nashville TN

Investigators

Abstract

In the last few years, NSF's Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the first gravitational waves emitted from a black-hole merger, and the NSF-supported Event Horizon Telescope (EHT) has captured the first electromagnetic images of an astrophysical black hole. Over the next two decades, future extensions of these gravitational-wave and radio interferometers are expected to deliver increasingly precise observations of two seemingly disparate (but in reality, deeply connected) phenomena: the “photon ring” of light that orbited around a supermassive black hole, and the late-time quasinormal-mode “ringdown” of a post-merger black hole. During this project, a team of researchers based at Vanderbilt University will elucidate the theoretical connections between these two seemingly disparate phenomena and produce new predictions for the next generation of planned gravitational experiments. At the same time, this team will develop an open-source interactive visual exhibit that illustrates black hole lensing, to be displayed at LIGO’s Science Education Centers. Although the photon ring in black hole images and the quasinormal-mode ringdown in gravitational waveforms may at first sight appear to be entirely different phenomena, they are in fact closely related in the eikonal limit of high frequency: in that regime, waves of massless fields (such as electromagnetic or gravitational waves) can be constructed out of null congruences of geodesics, and under the so-called geometric optics approximation, the quasinormal modes of a black hole correspond precisely to the nearly bound photon orbits whose images form its photon ring. The team funded by this award will refine and extend this theoretical connection, will exploit it to analytically study the quasinormal modes of a Kerr black hole and shed light on their spectral instability, and will use it to explore an emergent conformal symmetry that governs the photon ring and its associated quasinormal-mode spectrum. In a parallel line of research, this team will also elucidate how black hole images encode spin information within the photon ring and in polarized near-horizon emission and will then identify sharp signatures of electromagnetic energy extraction from a black hole’s spin energy. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.