Mass (1) primarily determines whether a giant star or supergiant star will form. Stars form in areas of high density in the interstellar region. These regions are known as molecular clouds and consist mainly of hydrogen. Helium, as well as other elements, are also found in this region. Giant and supergiant stars, as well as other stars, are formed by fusing hydrogen into helium in the central core of the star. The weights of the different stars have different properties at the different stages of their development.