Astronomers have probed the inner life of a dead star. Tiny changes in a white dwarf’s brightness reveal that the stellar corpse has more oxygen in its core than expected, researchers report online January 8 in Nature. The finding could challenge theories of how stars live and die, and may have implications for measuring the expansion of the universe.
As a star ages, it sheds most of its gas into space until all that remains is a dense core of carbon and oxygen, the ashes of a lifetime of burning helium (SN: 4/30/16, p. 12). That core, plus a thin shellacking of helium, is called a white dwarf.
But the proportion of those elements relative to one another was uncertain. “From theory, we have a rough idea of how it’s supposed to be, but we have no way to measure it directly,” says astrophysicist Noemi Giammichele, now at the Institute of Research in Astrophysics and Planetology in Toulouse, France.
Luckily, some white dwarfs encode their inner nature on their surface. These stars change their brightness in response to internal vibrations. Astrophysicists can infer a star’s internal structure from the vibrations, similar to how geologists learn about Earth’s interior by measuring seismic waves during an earthquake.
Giammichele and her colleagues used data from NASA’s Kepler space telescope, which watched stars unblinkingly to track…
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