  White dwarfs are the burnt out cores of Sun-like stars and are the final fate
of 97% of all stars in our Galaxy. The internal structure and composition of
white dwarfs are hidden by their high gravities, which causes all elements,
apart from the lightest ones, to settle out of their atmospheres. The most
direct method to probe the inner structure of stars and white dwarfs in detail
is via asteroseismology. Here we present the first known pulsating white dwarf
in an eclipsing binary system, enabling us to place extremely precise
constraints on the mass and radius of the white dwarf from the light curve,
independent of the pulsations. This 0.325M$_\odot$ white dwarf --- one member
of SDSS J115219.99+024814.4 --- will serve as a powerful benchmark to constrain
empirically the core composition of low-mass stellar remnants and investigate
the effects of close binary evolution on the internal structure of white
dwarfs.

Solar and Stellar Astrophysics