Session E01: Testing General Relativity

Live

The LIGO and Virgo gravitational wave detectors carried out the first half of their third observing run from April through October, 2019, collecting 39 new detections of compact binary coalescences. These and previously detected signals contain invaluable information about the nature of black holes and the properties of spacetime more generally. In this talk, I will summarize recent results along this front. This includes updated constraints on deviations from the predictions of general relativity for the generation and propagation of gravitational waves, searches for echos, and probes of the behavior of ringing black holes. I will close by outlining future prospects for testing Einstein’s theory with gravitational waves.   

Live

In April of 2019 the Event Horizon Telescope (EHT) published the first image of a supermassive black hole resolved to event horizon scales. This image led to the first measurement of the size of a black-hole shadow, the shadow that the black hole casts on the surrounding emission. We use analytic calculations and numerical simulations to place constraints on regular, parametric, non-Kerr metrics and to identify the common characteristic among these different parametrizations that controls the predicted shadow size. We also connect our work to previous tests and show that spacetimes that deviate from the Kerr metric but satisfy weak-field tests can lead to large deviations in the predicted black-hole shadows that are inconsistent with even the current EHT measurements.   

Live

Theoretical attempts to explain dark energy or unify gravity with the other fundamental interactions include new phenomena such as extra spatial dimensions, chameleons, or string theory moduli which would also violate the gravitational inverse-square law at small separations. In our most recent search for such violations, we used a stationary torsion-pendulum suspended above a rotating attractor to measure highly-resolved gravitational torques at separations between 3 mm and 52 $\mu$m. The pendulum and attractor test-masses featured an optimized Fourier-Bessel geometry with 18-fold and 120-fold symmetric annular sections cut from 50 $\mu$m thick platinum foils. I will present a description of our instrument, analysis, and the results from these most recent measurements.