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Odd white dwarf found with mostly oxygen atmosphere

Something stripped dead star of its hydrogen and helium, providing rare peek into its core

2:00pm, March 31, 2016
White dwarf and Sirius

RARE AIR  A newly discovered white dwarf has an atmosphere unlike any other — it’s loaded with oxygen. Hydrogen and helium dominate the atmospheres of more typical white dwarfs, such as this one (lower left) snuggled up to Sirius (center), the brightest star in the night sky.

White dwarfs — the exposed cores of dead stars — are the last place astronomers expected to find an oxygen atmosphere. Yet that’s exactly what recently turned up, providing researchers a rare peek inside the core of a massive star and raising questions about how such an oddball could have formed.

Most stars die by gently casting the bulk of their gas into space, leaving behind a dense, hot core. Heavy elements such as carbon and oxygen sink to the core’s center while hydrogen and helium float to the surface. But a newly discovered white dwarf, about 1,200 light-years away in the constellation Draco, has no hydrogen or helium at its surface. Its atmosphere is instead dominated by oxygen, researchers report in the April 1 Science.

“We only found one, so it is a rare event,” says study coauthor Kepler de Souza Oliveira Filho, an astronomer at the Federal

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