It's not every day that one stumbles upon a one-of-a-kind dead star, but that's exactly what happened to a team of astronomers.
The Sloan Digital Sky Survey (SDSS) is a project that aims to map the Milky Way by measuring the spectral lines of light coming off of objects throughout the universe. These spectral lines can tell astronomers what types of elements make up a star's atmosphere.
Using SDSS data, astronomers were able to zero in on a white dwarf star — which was assigned the name, "SDSS J124043.01+671034.68" — that didn't have any hydrogen or helium in its atmosphere. Its surrounding air was almost pure oxygen.
In their paper published in the journal Science, astronomers Kepler de Souza Oliveira, Detlev Koester, and Gustavo Ourique explained,
"Stars born with masses below around 10 solar masses end their lives as white dwarf stars. Their atmospheres are dominated by the lightest elements because gravitational diffusion brings the lightest element to the surface."
"After oxygen, the next most abundant elements in (the atmosphere of SDSS J124043.01+671034.68) are neon and magnesium, but these are lower by a factor of ≥25 by number. The fact that no hydrogen or helium are observed is surprising. Oxygen, neon, and magnesium are the products of carbon burning, which occurs in stars at the high-mass end of pre–white dwarf formation."
The astronomers think this unique white dwarf may be the key to discovering more about the evolutionary paths of stars. They are now exploring several theories about how SDSS J124043.01+671034.68 came to be.
Citing the astronomers' initial theories, Loren Grush wrote in The Verge,
"One possible explanation for the lack of helium and hydrogen is that the star experienced a giant thermal pulse when it was a red giant, and that intense explosion stripped away all the lighter elements. Another possible scenario is that the star was actually part of a binary system. The stars may have merged together, causing an explosion that ejected the hydrogen and helium."
For now, though, the mystery surrounding the star's atmosphere remains.