I have a mass of 1.3 solar masses (For a white dwarf), and my aim is to find the radius of this mass.

I have used the relation R $\propto$ $M^{\frac{-1}{3}}$.

From here I multiplied using the solar mass and radius.

*$R_D =$ Radius of white dwarf, $R_S$ = Radius of the sun.

$\frac{R_D}{R_S}$ = ${(\frac{1.3M_S}{M_S}})^{\frac{-1}{3}}$

After multiplying across by $R_S$ I get a value of $R_D$ = 0.916 $R_S$ which is incorrect.

I would appreciate if someone could point out where I'm going wrong.


You need to know the mass density of a white dwarf. Your error was using the density of the sun. Wikipedia gives a reasonable calculation: "A white dwarf, then, packs mass comparable to the Sun's into a volume that is typically a million times smaller than the Sun's; the average density of matter in a white dwarf must therefore be, very roughly, 1,000,000 times greater than the average density of the Sun, or approximately 10^6 g/cm^3, or 1 tonne per cubic centimetre." https://en.wikipedia.org/wiki/White_dwarf


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.