What increases or decreases the mass and density of a fixed radius star? Assuming a relatively even proportion of mass and radius, a 0.25 solar masses and radii star would have a density of 22.5003 g/cm³, or about 16 times our Sun's density.
Keeping the radius of 0.25 solar radii, what influences would cause different 0.25 solar radii stars in the main sequence to have higher or lower masses/densities than the &quot;normal&quot; 0.25 solar masses?
Stars are broadly divided into 3 types. These 3 types are divided on the basis of their composition of gases and elements other than H and He. So even if these stars are of same radius, their composition is different.
I am not sure but I think that as different stars have different composition and their rate of fusion is different, their density is different and so is their mass. Also while some stars are just forming and are at that radius, their gas composition is different than what a dying star of that radius is and so their masses is different.
I don't know if my version of the answer is right, but I hope this helped.