Lucy in the sky with diamonds.
A star in the constellation of Centaurus has a secret at its heart. At first it appeared to be a dim white dwarf, but it subsequently turned out to be incredibly dense, with the mass of the Sun crammed into an object only a third the diameter of Earth.
It is also remarkably cool, with a core temperature of a mere 6,600°C (by comparison, the Sun is around 15 million°C). At these temperatures stars begin to vibrate, and astronomers can use these vibrations to peer inside a star. In this case, they found that the star’s carbon core had crystallised to form a diamond 10 billion trillion trillion carats in size. The star was later nicknamed Lucy, after the Beatles song ‘Lucy in the Sky with Diamonds’.
Since the discovery of Lucy, several other crystallised stars have been found, some with diamond hearts the size of Earth.