Testing the No-Hair Theorem with Event Horizon Telescope Observations of Sagittarius A*

Understand

The advent of the Event Horizon Telescope (EHT), a millimeter-wave very-long baseline interferometric array, has enabled spatially-resolved studies of the sub-horizon-scale structure for a handful of supermassive black holes.

• Among these, the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), presents the largest angular cross section.
• Thus far, these studies have focused upon measurements of the black hole spin and the validation of low-luminosity accretion models.
• However, a critical input into the analysis of EHT data is the structure of the black hole spacetime, and thus these observations provide the novel opportunity to test the applicability of the Kerr metric to astrophysical black holes.