Supernovae sparked by dark matter in white dwarfs

It was recently demonstrated that asymmetric dark matter can ignite supernovae by collecting and collapsing inside lone sub-Chandrasekhar mass white dwarfs, and that this may be the cause of Type Ia supernovae. A ball of asymmetric dark matter accumulated inside a white dwarf and collapsing under its own weight sheds enough gravitational potential energy through scattering with nuclei to spark the fusion reactions that precede a Type Ia supernova explosion. In this article we elaborate on this mechanism and use it to place new bounds on interactions between nucleons and asymmetric dark matter for masses $m_X={10}^6–{10}^{16}\mathrm{GeV}$. Interestingly, we find that for dark matter more massive than $10^{11}\mathrm{GeV}$, Type Ia supernova ignition can proceed through the Hawking evaporation of a small black hole formed by the collapsed dark matter. We also identify how a cold white dwarf’s Coulomb crystal structure substantially suppresses dark matter–nuclear scattering at low momentum transfers, which is crucial for calculating the time it takes dark matter to form a black hole. Higgs and vector portal dark matter models that ignite Type Ia supernovae are explored.

Figure 1

Minimum dark matter–nucleon cross section ${\sigma }_{nX}$ as a function of $m_X$, in a log-log plot, for dark matter to thermalize with the white dwarf (green and blue lines) and accumulate critical mass for self-gravitation (orange line) within 3 Gyrs. The minimum cross section for the thermalized dark matter sphere to collapse to a black hole (yellow line) within 3 Gyrs and for dark matter accumulation to preclude complete black hole evaporation (purple line) are also shown. A dark matter halo density ${\rho }_X\approx 0.3{\mathrm{GeV}/\mathrm{cm}}^3$ at the location of the white dwarf is assumed. The upper-left box shows the white dwarf parameters used, where the mass and age of the white dwarf were determined by the oldest massive white dwarf in the Montreal White Dwarf Database [50], SDSS $\mathrm{J}160420.40+055542.3$.

Figure 2

Constraints on the dark matter–nucleon cross section ${\sigma }_{nX}$, as a function of $m_X$, for Type Ia supernova ignition within 3 Gyrs, by either nuclear scattering or black hole evaporation (orange). Lines labeled “DM self-gravitation” (orange/green) and “${\sigma }_{nX}$ for ignition” (orange) denote the minimum ${\sigma }_{nX}$ for white dwarf ignition by nuclear scattering from requiring either that enough dark matter is captured so that it “self-gravitates” or that collapsing dark matter scatters frequently enough to ignite the white dwarf. The line labeled “DM collapse” (orange/green) limits the parameter space where dark matter will not ignite the white dwarf during collapse, but instead collapses and forms a black hole. Complete evaporation of this black hole via Hawking radiation ignites the white dwarf. The line “DM feeds BH” (purple) denotes the limiting region where black hole evaporation is potentially stalled by further dark matter capture (see Fig. 1). The region “BH implodes WD” (green) is the parameter space where a black hole that consumes the white dwarf would be formed. A dark matter halo density ${\rho }_X\approx 0.3{\mathrm{GeV}/\mathrm{cm}}^3$ at the location of the white dwarf is assumed. All bounds were obtained using the parameters displayed in the lower right, taken from an old white dwarf (SDSS $\mathrm{J}160420.40+055542.3$) selected to provide the most stringent bound for $m_X\lesssim {10}^8\mathrm{GeV}$, out of all single white dwarfs listed in the Montreal White Dwarf Database [50]. See Appendix for an extended discussion of bounds obtained from different white dwarfs, including those in old globular clusters [14]. Also displayed are the bounds obtained from the Xenon-1T experiment (blue line) [51] and neutron star implosions (yellow line) [29].

Figure 3

Constraints on the mixing parameter ${\epsilon }_{\gamma }$ for vector $\varphi$ as a function of its mass $m_{\varphi }$, in a log-log plot. We fix ${\alpha }_X={10}^{-1}$ (note the linear dependence of the cross section on this parameter). The different colors correspond to different dark matter masses, as labeled. Regions above the solid lines are excluded by observations of the old white dwarf SDSS $\mathrm{J}160420.40+055542.3$. Shaded regions denote parameter space bounded by supernova cooling and particle colliders [78, 79, 80, 81, 82, 83, 84]. We have omitted constraints on dark photons that would decay during and thereby alter primordial nuclear abundances from big bang nucleosynthesis [85].

Figure 4

Constraints on the mixing parameter ${\epsilon }_h$ for scalar $\varphi$ as a function of its mass $m_{\varphi }$, in a log-log plot. We fix ${\alpha }_{\varphi }={10}^{-1}$ (note the linear dependence of the cross section on this parameter). The different colors correspond to different dark matter masses; regions above these colored lines are excluded by observation of the old white dwarf SDSS $\mathrm{J}160420.40+055542.3$. Shaded parameter space is excluded by nonobservation of anomalous meson decays at the CHARM experiment [87]. There are additional constraints on the Higgs portal scalar from cosmological considerations, including contributions to relativistic degrees of freedom, distortions of the cosmic microwave background, and primordial nucleosynthesis abundances [88].

Figure 5

Constraints on the dark matter–nucleon scattering cross section, as in Fig. 2. Here we show the total parameter space excluded by observation of three different old white dwarfs taken from the Montreal White Dwarf Database [50]: SDSS $\mathrm{J}160420.40+055542.3$ has a mass $\sim 1.4M_{\odot }$ and is $\sim 3\mathrm{Gyr}$ old; SDSS $\mathrm{J}073011.24+164800.0$ has a mass $\sim 1.3M_{\odot }$ and is $\sim 5\mathrm{Gyr}$ old; and SDSS $\mathrm{J}134113.16+010027.8$ has a mass of $\sim 1.1M_{\odot }$ and is $\sim 9\mathrm{Gyr}$ old. For dark matter masses up to $m_X\approx {10}^8\mathrm{GeV}$, the bound on the cross section is determined by the requirement that dark matter collects into a self-gravitating mass at the core of the white dwarf. For larger dark matter masses ($m_X\gtrsim {10}^8\mathrm{GeV}$), the bound depends only on the age of the white dwarf and is relatively insensitive to the white dwarf’s composition; see text for details.