HairyNevus writes "A recent survey of pulsars has revealed a fascinating discovery of a millisecond pulsar in system PSR J17191438 that has stripped a nearby white dwarf star down to its very core. Although no longer visible, is still has the mass of Jupiter. The remaining core rotates its neutron star companion with a period of just under 2 hours, indicating extremely close proximity. Given this distance, scientists have calculated that the substance of the core must be very compact, and, without building up the point, they conclude it is made of diamond. One thing I found misleading about the article is that it refers to the core as having 'the size of Jupiter' and 'the mass of Jupiter.' Given their different densities (diamond vs. mostly helium), it would seem clear that their size (i.e. volume) differs."