Astronomers found a dead star with a core made of solid diamond
Fifty light-years away sits BPM 37093, a dying white dwarf star nicknamed Lucy after the Beatles song 'Lucy in the Sky with Diamonds.' As the star burned through its nuclear fuel, it cooled and compressed its vast core of carbon and oxygen. Over billions of years, the carbon crystallized into a massive cosmic diamond estimated at 10 billion trillion trillion carats, dwarfing any gemstone ever found on Earth.
A Stellar Remnant in Centaurus
Roughly fifty light-years from Earth, in the southern constellation of Centaurus, lies an unassuming stellar remnant cataloged as BPM 37093. To an ordinary optical telescope, it appears only as a faint, dim point of light. Yet this object represents the dense, collapsed core of an evolved star that exhausted its nuclear fuel long ago. Having shed its outer layers into space, BPM 37093 entered the final evolutionary stage available to intermediate-mass stars: the white dwarf phase.
White dwarfs are among the densest forms of matter in the universe, packing a mass comparable to that of our Sun into a volume no larger than Earth. In the case of BPM 37093, astronomers determined that its mass is unusually high for a white dwarf, measuring approximately 1.1 times the mass of the Sun. Because it can no longer generate energy through nuclear fusion, it survives by radiating away its residual thermal energy over billions of years, slowly cooling into the deep freeze of interstellar space.
From Burning Plasma to a Crystal Lattice
The interior of a typical intermediate-mass white dwarf consists primarily of carbon and oxygen, the ash left behind by earlier helium-burning phases. When the star is young and hot, these atomic nuclei swim freely in a dense sea of electrons, supported against total gravitational collapse by electron degeneracy pressure. In this state, the interior behaves as an exotic, ultra-dense plasma held under incomprehensible gravitational forces.
Theoretical astrophysicists predicted decades ago that as a white dwarf radiates its heat into space, the temperature at its center eventually drops below a critical threshold. Under the immense pressure generated by the star's gravity, the freely moving carbon and oxygen nuclei can no longer maintain their fluid arrangement. Instead, they lock into an orderly, repeating three-dimensional lattice. In effect, the cooling carbon crystallizes into a giant, solid structure analogous to diamond, while the oxygen separates and settles according to its density.