tself, then it has become a protostar. The temperature of a protostar's surface is about 4000 K, and energy in its deep interior is transported to the surface entirely by convection. Eventually, temperature and luminosity Artistic Depiction of Protostarrise to the highest level that they can reach on the H-R diagram and the protostar becomes a pre-main sequence star. At this point its radius is about the same as the Earth's distance from our Sun. Gravity eventually raises the temperature in a protostar's core to 1 million K and past, which is hot enough to even melt some of the lighter metals on the periodic table. Eventually when the core reaches a temperature of a few million degrees or more, the burning of Hydrogen begins. When that happens, it ignites for the first time and shines as an adult star. The ignition blows off the remaining rocks and dust that, before this point in time, covered the protostar from our spying eyes. After a certain amount of time, the core reaches a critical point where it begins to resist the force of gravity and its compression slows. Astronomers define the zero-age main sequence as the point when a protostar stops contracting, becomes stable, and they get all their luminosity by burning hydrogen. To give you an idea of how long it takes for a star to go from the stage of being a protostar to the point where hydrogen burning begins and the star becomes stable, it took our Sun about 30 million years to bridge that gap. Stars that are larger than our Suns mass bridge this gap quite quickly, while for the smaller stars, the protostar period is much longer than that for the Sun. (Hansen, 1994)Our star has now formed and it has finally reached its adult stage of life. The adult star is not very interesting at all. It contains mostly hydrogen and it will burn for much longer than you or I could even possibly begin to imagine. The hydrogen inside the star is converted into helium by the means...
