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White dwarf’s inner makeup is mapped for the first time

The stellar corpse is richer in oxygen than expected, challenging long-standing theories about stellar evolution

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11:00am, January 8, 2018
illustration of inner structure of a white dwarf

WHAT LIES WITHIN  The inner structure of a white dwarf star (shown in this artist’s impression) has been mapped for the first time — and it’s more oxygen-rich than expected.

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.

By the end of a sunlike star’s life, it has shed 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

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