How did density fluctuations in the early universe help form galaxies?

In the early universe, shortly after the big bang, matter was not distributed perfectly uniformly. Instead, the universe contained small density fluctuations—regions where matter was slightly more concentrated than in others.12

These fluctuations were crucial for galaxy formation because they acted as gravitational seeds. As the universe expanded and cooled, these denser regions exerted a stronger gravitational pull than their surroundings, causing them to attract more matter. Over time, these areas condensed into small clouds known as protogalaxies, which eventually collapsed under their own gravity to form galaxies.13

Dark matter played a vital role in this process. Because it is abundant and interacts primarily through gravity, it provided the necessary mass to accelerate the coalescence of these structures. Observations of the cosmic microwave background have confirmed these early irregularities, showing that they provided the essential framework upon which the stars and galaxies of the modern universe were built.432