Do primordial black holes born from phase transitions spin faster?

When the early universe undergoes first-order phase transitions, bubbles nucleate at different times across space, creating non-spherical overdense regions that collapse into primordial black holes. By tracking how nucleation timing shapes these collapsing blobs' geometry and velocity shear, the authors calculate how much spin (Kerr parameter) these black holes acquire—finding it reaches 10^−3, substantially more than predicted by standard radiation-era models but less than matter-era predictions.