Type-Ia supernovae are probably thermonuclear explosions of accreting white dwarfs that have approached or reached the Chandrasekhar limit. a. Use the virial theorem to obtain an expression for the mean pressure inside a white dwarf of mass M and radius R. b. Use the result of (a) to estimate, to an order of magnitude, the speed of sound, vs = p dP/drho ∼ p P/rho, inside a white dwarf. In an accreting white dwarf with a carbon core that has reached nuclear ignition temperature, a nuclear burning "flame" encompasses the star at the sound velocity or faster. Within how much time, in seconds, does the flame traverse the radius of the white dwarf, assuming R = 104 km, M = 1.4M¯? Note that this soundcrossing timescale is ∼ (Grho) −1/2 , which is also the free-fall timescale (Eq. 3.15.)