Superradiance in rotating stars and pulsar-timing constraints on dark photons

Understand

In the presence of massive bosonic degrees of freedom, rotational superradiance can trigger an instability that spins down black holes.

• This leads to peculiar gravitational-wave signatures and distribution in the spin-mass plane, which in turn can impose stringent constraints on ultralight fields.
• Here, we demonstrate that there is an analogous spindown effect for conducting stars.
• We show that rotating stars amplify low frequency electromagnetic waves, and that this effect is largest when the time scale for conduction within the star is of the order of a light crossing time.