Main-Sequence Classification
Sirius as of right now is not expanding or contracting. This is because it is a main sequence star which is the most stable part of a stars life so there is no growing or shrinking. Picture it as this, when you grow up, there is a time that you do not grow any more before you start to shrink some until your death. This is the same concept that applies to most if not all main sequence stars.
Parts of a Star - Sun Example
(Core to Outside) Inner Core - The core of the star is where nuclear fusion occurs, nuclear fusion can occur here because the temperature and pressure are high enough to allow it. Radiative Zone - The radiative zone is where the gamma radiation energy is mainly developed. This zone helps the photons move to the surface of the star. Convection Zone - The convection zone is what takes the energy to the surface. There are hot gases which take energy to the surface, once it breaks the surface the gases become cold and sink to get more energy. Photosphere - This is the outer layer or "crust" of the sun (star). This is what we see when we look at the sun. Chromosphere - The Chromosphere or "sphere of color" is an outer shell that glows due to how hot a star is. On the sun, it can be most easily seen in a total solar eclipse. |