Astronomers have discovered the smallest yet most massive white dwarf star ever seen.

According to a new study published Thursday in the journal Nature, the “very special” star has a mass greater than that of our sun, all packed into a relatively small body, similar in size to our moon. It formed when two less massive white dwarf stars, which spent their lives as a pair orbiting around each other, collided and merged together.

At the end of their lives, the vast majority of stars become white dwarfs, which are essentially smoldering corpses, in addition to being one of the densest objects in the universe alongside black holes and neutron stars. In about 5 billion years, our sun will become a red giant before ultimately suffering the same fate.