Scientists have discovered a ten billion trillion trillion carat diamond star.

The star, nicknamed "Lucy" (after the Beatles song "Lucy in the Sky with Diamonds"), is the crystallized core of a white dwarf, measuring some 4,000 km wide. A white dwarf is the leftover core of a star that remains after the star uses up all its fuel and dies.

Scientists have long suspected that white dwarf cores crystallized, but were never sure until discovering BPM 37093 (Lucy's technical name). Our very own sun is expected to become a white dwarf when it dies in 5 billion years, and 2 billion years after that, its core will also crystallize!
(source)