Varhaiskeskisistä

Varhaiskeskisistä refers to a specific stage in the development of a star, occurring after the protostar phase and before the main sequence phase. This stage is characterized by the star's core temperature and pressure increasing significantly, leading to the ignition of deuterium fusion. Deuterium is an isotope of hydrogen with one proton and one neutron in its nucleus. The fusion of deuterium releases energy, which helps to stabilize the star's core and prevent further gravitational collapse.

During the varhaiskeskisistä stage, the star's luminosity increases rapidly, and it begins to contract and heat up. This process continues until the core temperature reaches approximately 10 million Kelvin, at which point hydrogen fusion begins. The star then enters the main sequence phase, where it spends the majority of its life fusing hydrogen into helium in its core.

The varhaiskeskisistä stage is relatively short, lasting only a few million years for most stars. However, for very low-mass stars, this stage can last up to 100 million years or more. During this time, the star's properties, such as its radius and luminosity, evolve significantly, and it may undergo periods of instability and variability.

The study of varhaiskeskisistä stars is important for understanding the early stages of stellar evolution and the processes that govern the formation and evolution of stars. Observations of these stars can provide insights into the physical conditions in the early universe and the mechanisms that drive stellar evolution.