THE LONG-TERM EVOLUTION OF DOUBLE WHITE DWARF MERGERS

By K. Shen, L. Bildsten, D. Kasen, E. Quataert. 2011

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In this paper, we present a model for the long-term evolution of the merger of two unequal mass C/O white dwarfs (WDs). After the dynamical phase of the merger, magnetic stresses rapidly redistribute angular momentum, leading to nearly solid-body rotation on a viscous timescale of 10−4–1 yr, long before significant cooling can occur. Due to heating during the dynamical and viscous phases, the less massive WD is transformed into a hot, slowly rotating, and radially extended envelope supported by thermal pressure. Following the viscous phase of evolution, the maximum temperature near the envelope base may already be high enough to begin off-center convective carbon burning. If not, Kelvin–Helmholtz contraction of the inner region of the envelope on a thermal timescale of 103–104 yr compresses the base of the envelope, again yielding off-center burning. As a result, the long-term evolution of the merger remnant is similar to that seen in previous calculations: the burning shell diffuses inward over ∼104 yr, eventually yielding a high-mass O/Ne WD or a collapse to a neutron star, rather than a Type Ia supernova. During the cooling and shell-burning phases, the merger remnant radiates near the Eddington limit. Given the double WD merger rate of a few per 1000 yr, a few dozen of these ∼1038 erg s−1 sources should exist in a Milky Way type galaxy. While the end result is similar to that of previous studies, the physical picture and the dynamical state of the matter in our model differ from previous work. Furthermore, substantial remaining uncertainties related to the convective structure near the photosphere and mass loss during the thermal evolution may significantly affect our conclusions. Thus, future work within the context of the physical model presented here is required to better address the eventual fate of double WD mergers, including those for which one or both of the components is a He WD.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/dd134b317e60cf58edd4ff1e87d94d2cbf7cee30

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Citations in the corpus

Supernova Type Ia progenitors from merging double white dwarfs - Using a new population synthesis model (2012, background): “A serious concern about the DD scenario is whether the collapse of the remnant would lead to a supernova or to a neutron star through accretion-induced collapse (see Nomoto & Iben 1985; Saio & Nomoto 1985; Piersanti et al. 2003; Yoon et al. 2007; Pakmor et al. 2010, 2012; Shen et al. 2012).”
Predicting the LISA white dwarf binary population in the Milky Way with cosmological simulations (2019, background): “Depending on the masses of the systems, such mergers may lead to type Ia supernovae (Iben & Tutukov 1984) or other transients (Saio & Nomoto 2004; Shen et al. 2012).”
The delay-time distribution of Type Ia supernovae from Sloan II (2012, background): “…collapse to a neutron star, i.e. a core-collapse (CC) SN (although not a typical one, due to the absence of an envelope), rather than a SN Ia (Nomoto & Iben 1985; Shen et al. 2012), but ways have been proposed to avoid this (e.g. Pakmor et al. 2010; van Kerkwijk, Chang & Justham 2010).”
Observational Clues to the Progenitors of Type Ia Supernovae (2013, background): “…tidally disrupt and accrete the lower-mass WD, initially through an accretion disk configuration, that then likely takes on a more spherical geometry (e.g., Lorén-Aguilar, Isern & Garćıa-Berro 2009; Moll et al. 2013; Pakmor et al. 2012; Raskin et al. 2012; Schwab et al. 2012; Shen et al. 2012).”