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

TL;DR

This study measures the fraction of rapidly rotating massive stars in metal-poor dwarf galaxies, revealing that such extreme rotators are common in low-metallicity environments like the early universe.

Contribution

Introduces a new photometric method to measure OBe star fractions across multiple dwarf galaxies, expanding understanding of stellar rotation in metal-poor environments.

Findings

OBe star fraction is ~20% in the LMC.

OBe star fraction is ~30% in the SMC.

High OBe fractions suggest rapid rotation is common in early universe conditions.

Abstract

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 Magellanic Cloud (0.5 Z_Solar), and ~30% in the Small Magellanic Cloud (0.2 Z_Solar) as well as in the so-far unexplored metallicity range from 0.1 Z_solar to 0.2 Z_solar 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.