In 1863, a telescope maker named Alvan Clark discovered why a star known as Sirius seemed to wobble back and forth. It had a companion star, difficult to see because it is a white dwarf - the faintly glowing lump of carbon that is left over after stars burn through their fuel. The binary system is now known as Sirius A and Sirius B, and white dwarf stars have fascinated astronomers ever since.
Now physicists at Sandia National Laboratory in New Mexico are getting into the white dwarf game, collaborating with their astronomer colleagues to recreate the atmospheres of white dwarf stars in the lab. Their instrument? A powerful x-ray-generating machine at Sandia known as the "Z-pinch."
When we see the light from white dwarf stars, we're not seeing the glow from the carbon embers because there is a thin layer of dense gas getting the way, pulled in by the star's gravity. It is the gas - an atmosphere of sorts, made up primarily of hydrogen - that emits the light.
There are other elements present, too, most notably helium, certain metals, and of course, carbon. We know this because astronomers have used spectroscopy to identify those elements - a technique that measures the telltale frequencies at which different elements absorb and emit light.