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Title: SPIRAL INSTABILITY CAN DRIVE THERMONUCLEAR EXPLOSIONS IN BINARY WHITE DWARF MERGERS

Abstract

Thermonuclear, or Type Ia supernovae (SNe Ia), originate from the explosion of carbon–oxygen white dwarfs, and serve as standardizable cosmological candles. However, despite their importance, the nature of the progenitor systems that give rise to SNe Ia has not been hitherto elucidated. Observational evidence favors the double-degenerate channel in which merging white dwarf binaries lead to SNe Ia. Furthermore, significant discrepancies exist between observations and theory, and to date, there has been no self-consistent merger model that yields a SNe Ia. Here we show that a spiral mode instability in the accretion disk formed during a binary white dwarf merger leads to a detonation on a dynamical timescale. This mechanism sheds light on how white dwarf mergers may frequently yield SNe Ia.

Authors:
;  [1]; ;  [2];  [3];  [4]
  1. Department of Physics, University of Massachusetts Dartmouth, 285 Old Westport Road, North Dartmouth, MA 02740 (United States)
  2. Departament de Física Aplicada, Universitat Politècnica de Catalunya, c/Esteve Terrades, 5, E-08860 Castelldefels (Spain)
  3. Department of Physics, Broida Hall, University of California Santa Barbara, Santa Barbara, CA 93106–9530 (United States)
  4. School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)
Publication Date:
OSTI Identifier:
22364257
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 800; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; CARBON; HYDRODYNAMICS; OXYGEN; SUPERNOVAE; THERMONUCLEAR EXPLOSIONS; VISIBLE RADIATION; WHITE DWARF STARS

Citation Formats

Kashyap, Rahul, Fisher, Robert, García-Berro, Enrique, Aznar-Siguán, Gabriela, Ji, Suoqing, and Lorén-Aguilar, Pablo. SPIRAL INSTABILITY CAN DRIVE THERMONUCLEAR EXPLOSIONS IN BINARY WHITE DWARF MERGERS. United States: N. p., 2015. Web. doi:10.1088/2041-8205/800/1/L7.
Kashyap, Rahul, Fisher, Robert, García-Berro, Enrique, Aznar-Siguán, Gabriela, Ji, Suoqing, & Lorén-Aguilar, Pablo. SPIRAL INSTABILITY CAN DRIVE THERMONUCLEAR EXPLOSIONS IN BINARY WHITE DWARF MERGERS. United States. doi:10.1088/2041-8205/800/1/L7.
Kashyap, Rahul, Fisher, Robert, García-Berro, Enrique, Aznar-Siguán, Gabriela, Ji, Suoqing, and Lorén-Aguilar, Pablo. 2015. "SPIRAL INSTABILITY CAN DRIVE THERMONUCLEAR EXPLOSIONS IN BINARY WHITE DWARF MERGERS". United States. doi:10.1088/2041-8205/800/1/L7.
@article{osti_22364257,
title = {SPIRAL INSTABILITY CAN DRIVE THERMONUCLEAR EXPLOSIONS IN BINARY WHITE DWARF MERGERS},
author = {Kashyap, Rahul and Fisher, Robert and García-Berro, Enrique and Aznar-Siguán, Gabriela and Ji, Suoqing and Lorén-Aguilar, Pablo},
abstractNote = {Thermonuclear, or Type Ia supernovae (SNe Ia), originate from the explosion of carbon–oxygen white dwarfs, and serve as standardizable cosmological candles. However, despite their importance, the nature of the progenitor systems that give rise to SNe Ia has not been hitherto elucidated. Observational evidence favors the double-degenerate channel in which merging white dwarf binaries lead to SNe Ia. Furthermore, significant discrepancies exist between observations and theory, and to date, there has been no self-consistent merger model that yields a SNe Ia. Here we show that a spiral mode instability in the accretion disk formed during a binary white dwarf merger leads to a detonation on a dynamical timescale. This mechanism sheds light on how white dwarf mergers may frequently yield SNe Ia.},
doi = {10.1088/2041-8205/800/1/L7},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 800,
place = {United States},
year = 2015,
month = 2
}
  • We carry out a comprehensive smooth particle hydrodynamics simulation survey of double-degenerate white dwarf binary mergers of varying mass combinations in order to establish correspondence between initial conditions and remnant configurations. We find that all but one of our simulation remnants share general properties such as a cold, degenerate core surrounded by a hot disk, while our least massive pair of stars forms only a hot disk. We characterize our remnant configurations by the core mass, the rotational velocity of the core, and the half-mass radius of the disk. We also find that some of our simulations with very massivemore » constituent stars exhibit helium detonations on the surface of the primary star before complete disruption of the secondary. However, these helium detonations are insufficiently energetic to ignite carbon, and so do not lead to prompt carbon detonations.« less
  • Recently, Thornton et al. reported the detection of four fast radio bursts (FRBs). The dispersion measures indicate that the sources of these FRBs are at cosmological distance. Given the large full sky event rate ∼10{sup 4} sky{sup –1} day{sup –1}, the FRBs are a promising target for multi-messenger astronomy. Here we propose double degenerate, binary white-dwarf (WD) mergers as the source of FRBs, which are produced by coherent emission from the polar region of a rapidly rotating, magnetized massive WD formed after the merger. The basic characteristics of the FRBs, such as the energetics, emission duration and event rate, canmore » be consistently explained in this scenario. As a result, we predict that some FRBs can accompany type Ia supernovae (SNe Ia) or X-ray debris disks. Simultaneous detection could test our scenario and probe the progenitors of SNe Ia, and moreover would provide a novel constraint on the cosmological parameters. We strongly encourage future SN and X-ray surveys that follow up FRBs.« less
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  • Type Ia supernovae (SNe Ia) are generally thought to be due to the thermonuclear explosions of carbon-oxygen white dwarfs (CO WDs) with masses near the Chandrasekhar mass. This scenario, however, has two long-standing problems. First, the explosions do not naturally produce the correct mix of elements, but have to be finely tuned to proceed from subsonic deflagration to supersonic detonation. Second, population models and observations give formation rates of near-Chandrasekhar WDs that are far too small. Here, we suggest that SNe Ia instead result from mergers of roughly equal-mass CO WDs, including those that produce sub-Chandrasekhar mass remnants. Numerical studiesmore » of such mergers have shown that the remnants consist of rapidly rotating cores that contain most of the mass and are hottest in the center, surrounded by dense, small disks. We argue that the disks accrete quickly, and that the resulting compressional heating likely leads to central carbon ignition. This ignition occurs at densities for which pure detonations lead to events similar to SNe Ia. With this merger scenario, we can understand the type Ia rates and have plausible reasons for the observed range in luminosity and for the bias of more luminous supernovae toward younger populations. We speculate that explosions of WDs slowly brought to the Chandrasekhar limit-which should also occur-are responsible for some of the 'atypical' SNe Ia.« less
  • 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{sup -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 enoughmore » to begin off-center convective carbon burning. If not, Kelvin-Helmholtz contraction of the inner region of the envelope on a thermal timescale of 10{sup 3}-10{sup 4} 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 {approx}10{sup 4} 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 {approx}10{sup 38} erg s{sup -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.« less