Constraining the Existence of Axion Clouds in M87* with Closure Trace Analyses

Understand

Black holes can amplify incoming bosonic waves via rotational superradiance, inducing bound states of ultralight bosons around them.

• This phenomenon has the potential to confine the parameter spaces of new bosons.
• Axions and axion-like particles (ALPs) are candidate beyond-standard-model particles that can form such clouds around supermassive black holes (SMBHs) and impact the polarization signal in a similar fashion to Faraday rotation via axion-photon coupling.
• Prior efforts have used polarized images from the Event Horizon Telescope (EHT) M87 2017 observations to limit the dimensionless axion-photon coupling to previously unexplored regions.