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Understanding stellar birth requires observations of the clouds in which theyform. These clouds are dense and self-gravitating, and in all existingobservations, they are molecular with H_2 the dominant species and CO the bestavailable tracer. When the abundances of carbon and oxygen are low compared tohydrogen, and the opacity from dust is also low, as in primeval galaxies andlocal dwarf irregular galaxies, CO forms slowly and is easily destroyed, so itis difficult for it to accumulate inside dense clouds. Here we reportinterferometric observations of CO clouds in the local group dwarf irregulargalaxy Wolf-Lundmark-Melotte (WLM), which has a metallicity that is 13% of thesolar value and 50% lower than the previous CO detection threshold. The cloudsare tiny compared to the surrounding atomic and H_2 envelopes, but they havetypical densities and column densities for CO clouds in the Milky Way. Thenormal CO density explains why star clusters forming in dwarf irregulars havesimilar densities to star clusters in giant spiral galaxies. The low cloudmasses suggest that these clusters will also be low mass, unless somegalaxy-scale compression occurs, such as an impact from a cosmic cloud or othergalaxy. If the massive metal-poor globular clusters in the halo of the MilkyWay formed in dwarf galaxies, as is commonly believed, then they were probablytriggered by such an impact.

Dense cloud cores revealed by CO in the low metallicity dwarf galaxy WLM