About 900 light-years away, an ancient white dwarf star has cooled into a crystallized chunk of carbon — a diamond. But this isn’t just any old diamond hiding in space: It’s the size of Earth, and it’s 11 billion years old.

The diamond-star, described in a study published in The Astrophysical Journal, is among the coldest white dwarfs astronomers have found. In fact, it’s so cool and dim that it can’t even be seen — its feeble light isn’t nearly powerful enough to pierce the darkness of the cosmos, even from relatively nearby.

Instead, teams inferred the presence of the crystallized dwarf based on the way its gravity perturbs the normally steady radio pulses coming from a spinning companion star.

Yep,