The universe is expanding, and stars are forming within it. This might seem counterintuitive, given that the universe is expanding faster than gravity can pull matter together. However, the universe is not entirely uniform; it has regions with different densities, and these density fluctuations are the key to understanding star formation. The universe was born with a specific set of density fluctuations, and these fluctuations are imprinted in the cosmic microwave background (CMB). The CMB is a map of the temperature variations in the early universe, and it shows that the universe was born with a specific set of density fluctuations. These fluctuations are the seeds of structure in the universe, and they are the key to understanding how stars form. The universe is expanding, and the average density is decreasing. However, on small cosmic scales, the matter density can grow faster than the expanding universe dilutes it. This is due to the Meszaros effect, which states that the growth rate of any density imperfection is proportional to the matter density at that time divided by the radiation density at that time. The Meszaros effect is a good approximation when the overdensity/underdensity of a specific region is small compared to the average density, but it's insufficient when those overdense (or underdense) regions are sufficiently large (or small) compared to the average density. The universe was born with a specific set of density fluctuations, and these fluctuations are the key to understanding how stars form. The universe is expanding, and the average density is decreasing. However, on small cosmic scales, the matter density can grow faster than the expanding universe dilutes it. This is due to the Meszaros effect, which states that the growth rate of any density imperfection is proportional to the matter density at that time divided by the radiation density at that time. The Meszaros effect is a good approximation when the overdensity/underdensity of a specific region is small compared to the average density, but it's insufficient when those overdense (or underdense) regions are sufficiently large (or small) compared to the average density. The universe was born with a specific set of density fluctuations, and these fluctuations are the key to understanding how stars form.
