Stars and galaxies do not "emerge" from the cosmic microwave background (CMB) as time goes by when observing the earliest universe. The cosmic microwave background is the radiation left over from the early stages of the universe, specifically from a time known as the cosmic microwave background radiation era.
The CMB is a faint glow of electromagnetic radiation that permeates the entire observable universe. It was emitted when the universe was approximately 380,000 years old, during a phase called recombination. At that time, the universe became transparent to light, allowing photons to travel freely through space.
Stars and galaxies, on the other hand, formed much later in the history of the universe, through a process known as cosmic structure formation. Over billions of years, the gravitational interaction of matter, primarily dark matter, led to the formation of structures such as galaxies, galaxy clusters, and superclusters. These structures eventually hosted the formation of stars within them.
So, while the CMB provides valuable insights into the early universe, it does not directly show the formation of stars and galaxies. It serves as a snapshot of the universe when it transitioned from a hot, dense state to a cooler, more transparent one, providing valuable information about the early universe's conditions and helping to support the Big Bang theory.