How Did the First Galaxies Form?

-- | September 18, 2013

Question: From where did this initial cloud of gases and dust come? In other words, how did the cloud form? Why were these gases and this dust together in a cloud?
I read on another website that the cloud began to collapse because it was rotating. You say that the cloud began to rotate as it collapsed. I assume the discrepancy is because of either your or the other writer’s uncertainty. As the cloud collapsed, why would it have begun to rotate? What would have caused the cloud to collapse in your scenario? — John Paul

Answer: I presume that you are referring to the formation of galaxies. Starting from the beginning, the first galaxies are believed to have formed as a result of primordial fluctuations in the early universe that gravitationally attracted gas and dark matter to the denser areas. These structures became the first galaxies. These first galaxies began to collapse due to self gravity, with rotation being part of this process in order to dissipate energy via angular momentum. Remember too that that this early stage the universe was almost exclusively composed of hydrogen, helium, and dark matter. Soon after these first galaxies formed, the hydrogen and helium gas within them formed the first stars, many of which were quite massive, evolved quickly, and ended their short lives as supernovae. The supernova process expels processed matter into the interstellar medium of the young galaxies, matter that contains heavier elements (produced by the fusion process in those first young stars) and some dust. That process of gravitational collapse, stellar evolution, and enrichment of the interstellar medium in galaxies then continues until we get the universe filled with galaxies we see today.

Jeff Mangum

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