Massive stars in metal-poor dwarf galaxies are often extreme rotators

We probe how common extremely rapid rotation is among massive stars in the early universe by measuring the OBe star fraction in nearby metal-poor dwarf galaxies. We apply a new method that uses broad-band photometry to measure the galaxy-wide OBe star fractions in the Magellanic Clouds and three more distant, more metal-poor dwarf galaxies. We find OBe star fractions of ∼20% in the Large Magallanic Cloud (0.5Z_ȯ), and ∼30% in the Small Magellanic Cloud (0.2Z_ȯ) as well as in the so-far unexplored metallicity range 0.1 Z/Z_ȯ < 0.2 occupied by the other three dwarf galaxies. Our results imply that extremely rapid rotation is common among massive stars in metal-poor environments such as the early universe.