[Bubble] A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf

[Jay Benesch]

I missed this when it came out in Nature; found via Physics Today.

C+He-> O called into doubt by C:O ratio in standard stellar evolution 
model.

https://www.nature.com/articles/nature25136

N. Giammichele, S. Charpinet, G. Fontaine, P. Brassard, E. M. Green, V. 
Van Grootel, P. Bergeron, W. Zong & M.-A. Dupret

Here we report a measurement of the radial chemical stratification (of 
oxygen, carbon and helium) in the hydrogen-deficient white-dwarf star 
KIC08626021 (J192904.6+444708), independently of stellar-evolution 
calculations. We use archival data7,8 coupled with asteroseismic 
sounding techniques9,10 to determine the internal constitution of this 
star. We find that the oxygen content and extent of its core exceed the 
predictions of existing models of stellar evolution. The central 
homogeneous core has a mass of 0.45 solar masses, and is composed of 
about 86 per cent oxygen by mass. These values are respectively 40 per 
cent and 15 per cent greater than those expected from typical 
white-dwarf models. These findings challenge present theories of stellar 
evolution and their constitutive physics, and open up an avenue for 
calibrating white-dwarf cosmochronology11.