Kirimo is the closest known white dwarf to Kerbol
"Scientists have long speculated about the existence of remnant cores of dead stars, so when the white dwarf Kirimo was discovered, astronomers back on Kerbin scrambled to get a better look at this exotic object. A visit to Kirimo will be a glimpse into the future at the fate of Kerbol, and many of the other stars that light up the night sky."
Kirimo is a white dwarf, and is made primarily out of electron-degenerate matter. Kirimo retains about half of its original mass while still at about the size of Kerbin. This means that Kirimo has an unimaginable density (though still less dense than a neutron star or a black hole), so dense that a single nugget-sized piece of its surface would weigh an entire ton on Kerbin. Kirimo is also intensely hot, due to the residual heat left over from its main sequence stage (Kirimo likely used to be an A-type star, as stars typically lose half their mass after becoming white dwarfs).
It is thought that it will take Kirimo 10^15 years, or one quadrillion years, to cool sufficiently to become a black dwarf.