Question

What is the mass and diameter of a white dwarf?

Answer 1

They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth

Answer 2

The Mass of a white dwarf star will be set by its upper limit, known as the Chandrasekhar limit, which is about 1.4 Solar Masses. This is the upper limit of mass that a white dwarf can be. If it gains any more mass beyond this limit (through accretion from a binary star, or collision with another stellar object), the processes that keep it in equilibrium (that is the balance between gravitational collapse and electron degeneracy pressure) can no longer support it, and then a Type 1a supernova results.

As for radius \(R\), this is inversely proportional to the cube root of its mass \(M\), and can indeed be approximated to order of magnitude to be \[R\approx \frac{1}{M^{1/3}}\]. A more accurate approximation is given by \[R\approx \frac{N^{5/2}\hbar^2}{2mGM^{1/3}}\]where \(N\) is the number of electrons per unit mass (see degenerate Fermi-Dirac statistics for the meaning of this), \(\hbar\) is Planck's reduced constant, \(m\) is the electron mass, and \(G\) is the universal gravitational constant. See wiki's entry for white dwarfs for further details

Answer 3

So to put it into context of teh question, a white dwarfs mass is thought to be less than 1.4 Solar masses, with a radius or diameter dependent upon whatever that mass happens to be.