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How did tiny density differences in the early universe help galaxies form?

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Oval map of the cosmic microwave background radiation from NASA's WMAP mission, showing a mottled pattern of blue, green, yellow, and red representing temperature variations. — Cosmic microwave background A full-sky map produced by the Wilkinson Microwave Anisotropy Probe (WMAP) showing cosmic background radiation, a very uniform glow of microwaves emitted by the infant universe more than 13 billion years ago. Color differences indicate tiny fluctuations in the intensity of the radiation, a result of tiny variations in the density of matter in the early universe. According to inflation theory, these irregularities were the “seeds” that became the galaxies. WMAP's data support the big bang and inflation models, and cosmic microwave background is at the farthest limits of the observable universe.

The tiny density differences in the early universe, observed as temperature fluctuations in the cosmic microwave background, were essential for the formation of galaxies.12

These fluctuations, which amount to about one part in 100,000, represent the initial seeds of structure in an otherwise uniform universe. Approximately 380,000 years after the big bang, intense sound waves echoed through the dense, early universe, leaving an imprint of these density variations.12

These regions of slightly higher density provided the gravitational "pull" necessary for matter to begin coalescing. Over time, these areas condensed into small clouds known as protogalaxies, which collapsed under their own gravity to form the galaxies and clusters of galaxies we observe today. The presence of dark matter—which makes up a significant portion of the universe's composition—played a critical role in this process, as its gravitational influence helped accelerate the condensation of these structures from the early density fluctuations.2314