I'd never heard of solid stars with a crystal lattice.
Astronomers from The University of Texas at Austin and colleagues have used the 2.1-meter Otto Struve Telescope at the university's McDonald Observatory to discover pulsations from the crystalized remnant of a burnt-out star.
It is a white dwarf, a star at the end of its life cycle that is essentially just a burnt-out core, the ashy byproduct of previous epochs of nuclear fusion.
The star is unique in that much of it is likely suspended in a state more akin to a solid than a liquid or gas. The interiors of dying stars can become crystalized similar to the way in which frigid water freezes into ice, like the slow formation of glaciers in cooling ocean water.
"GD 518 is special because it is a very massive white dwarf: It has about 1.2 times the mass of the Sun, packed into a volume smaller than Earth,"...
... is now likely a white dwarf composed of oxygen and neon nuclei.
White dwarf stars no longer fuse elements in their interior to generate energy; they simply cool, like coal embers removed from a fire. But at a certain point the atomic nuclei in the star's interior get cool enough to begin to settle into a lattice structure and crystalize, just like water freezing into ice. This happens sooner in the interiors of more massive white dwarfs, and in the case of GD 518, it has likely started before the star had the right conditions to excite pulsations. [emphasis mine]