Definition of protogalaxy in US English:

protogalaxy

noun

Astronomy
  • A vast mass of gas from which a galaxy is thought to develop.

    • ‘The protogalaxy probably has since coalesced into a giant elliptical galaxy, he says.’
    • ‘According to current models, that's not enough time to allow for the formation of either the quasars that illuminate the atomic gas or the protogalaxies that harbor the first stars.’
    • ‘Those that are still around us bear the imprint of the chemical composition of the protogalaxy in their atmospheres, like living fossils of a bygone era in the history of the Earth.’

Pronunciation

protogalaxy

/ˌprōdōˈɡaləksē/