What specific type of star did Hubble search for to measure extragalactic distances?

Answer

Cepheid variables

Hubble utilized Cepheid variable stars, a method pioneered by Henrietta Swan Leavitt, which allowed the determination of immense distances based on the star's period of pulsation.

What specific type of star did Hubble search for to measure extragalactic distances?
LegacySpacegalaxyAstronomeruniverse