Convection Destroys the Core/Mantle Structure in Hybrid C/O/Ne White Dwarfs

Jared Brooks, Josiah Schwab, Lars Bildsten, Eliot Quataert, Bill Paxton

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

A hybrid C/O/Ne white dwarf (WD) - an unburned C/O core surrounded by an O/Ne/Na mantle - can be formed if the carbon flame is quenched in a super-AGB star or white dwarf merger remnant. We show that this segregated hybrid structure becomes unstable to rapid mixing within 2000 years of the onset of WD cooling. Carbon burning includes a weak reaction that removes electrons, resulting in a lower electron-to-baryon ratio () in the regions processed by carbon burning compared to the unburned C/O core, making the O/Ne mantle denser than the C/O core as the WD cools. This is unstable to efficient mixing. We use the results of models with different size C/O cores to quantify the rate at which the cores mix with the mantle as they cool. In all cases, we find that the WDs undergo significant core/mantle mixing on timescales shorter than the time available to grow the WD to the Chandrasekhar mass (M Ch) by accretion. As a result, hybrid WDs that reach M Ch due to later accretion will have lower central carbon fractions than assumed thus far. We briefly discuss the implications of these results for the possibility of SNe Ia from hybrid WDs.

Original languageEnglish (US)
Article numberL9
JournalAstrophysical Journal Letters
Volume834
Issue number2
DOIs
StatePublished - Jan 10 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • supernovae: general
  • white dwarfs

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