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Galaxies litter the cosmos by the hundreds of billions. But there could easily be many, many more. In the May issue of Scientific American, astronomer James E. Geach of McGill University explores why so little of the matter created in the big bang went on to become the raw material for making galaxies. One reason is a phenomenon called feedback—as galaxies accrete matter, they also spew gas back out into space. In the simulation below, a developing galaxy is undergoing feedback, ejecting material into intergalactic space as it grows.