Abstract
White dwarfs (WD) effectively act as high-gain amplifiers for relatively small energy deposits within their volume via their supernova instability. In this paper, we consider the ways a galactic abundance of $\mathcal{O}(1)$-charged massive relics (i.e., CHAMPs) could trigger this instability, thereby destroying old WD. The dense central core structure formed inside the WD when heavy CHAMPs sink to its center can trigger a supernova via injection of energy during collapse phases, via direct density-enhanced (pycnonuclear) fusion processes of carbon nuclei dragged into the core by the CHAMPs, or via the formation of a black hole (BH) at the center of the WD. In the latter scenario, Hawking radiation from the BH can ignite the star if the BH forms with a sufficiently small mass; if the BH instead forms at large enough mass, heating of carbon nuclei that accrete onto the BH as it grows in size may be able to achieve the same outcome (with the conservative alternative being simply that the WD is devoured by the BH). The known existence of old WD that have not been destroyed by these mechanisms allows us to improve by many orders of magnitude on the existing CHAMP abundance constraints in the regime of large CHAMP mass, $m_X \sim 10^{11}$-$10^{18}\,$GeV. Additionally, in certain regions of parameter space, we speculate that this setup could provide a trigger mechanism for the calcium-rich gap transients: a class of anomalous, sub-luminous supernova events that occur far outside of a host galaxy.
Highlights
Charged massive particles (CHAMPs),1 defined here as massive early-Universe relics with Oð1Þ electrical charge, appear in many theories of physics beyond the Standard Model; for instance, the (N)LSP in R-parity conserving supersymmetric extensions of the SM can be electrically charged andstable (e.g., Refs. [1,2]); theories of universal extra dimensions may have as their lightest KKodd state a charged state (e.g., Refs. [3,4]); and exotic stable composite bound states [5,6,7,8] may have an Oð1Þ net electrical charge without their stability being dramatically impacted
VI we examine in detail the accumulation of charged massive particles (CHAMPs) in white dwarfs and their behavior in such dense objects generally, with a particular focus on the dense central core structures they form in the WD, as well as the maximum supportable masses allowed before such cores undergo gravothermal collapse, or collapse to a black hole (BH)
There are a number of Appendixes that offer extra information: Appendix A is a discussion of the binding energies of X− with positively charged nuclei; Appendix B contains an estimate of the pycnonuclear fusion rate of carbons bound in ðCXÞ bound states in the central dense CHAMPcontaminated core of the WD; Appendix C gives the full expressions we use to compute the CHAMP abundance accreting onto a WD over its lifetime; Appendix D contains a detailed consideration both of canonical WD structure and CHAMP-contaminated WD structure; Appendixes E and F contain the expressions we have used for the electron heat conduction and free-free opacity, respectively, that are used in computing the WD trigger conditions
Summary
Charged massive particles (CHAMPs), defined here as massive early-Universe relics with Oð1Þ electrical charge, appear in many theories of physics beyond the Standard Model; for instance, the (N)LSP in R-parity conserving supersymmetric extensions of the SM can be electrically charged and (meta)stable (e.g., Refs. [1,2]); theories of universal extra dimensions may have as their lightest KKodd state a charged state (e.g., Refs. [3,4]); and exotic stable composite bound states [5,6,7,8] may have an Oð1Þ net electrical charge without their stability being dramatically impacted. The existence of observed old NSs can strongly constrain the abundance of CHAMPs. On the other hand, if the BH has an initial mass MBH ≲ MNBHS;crit:;, the mass loss by the BH due to Hawking radiation dominates the mass gain from accretion of NS matter, causing the BH to shrink in size and eventually evaporate. WDs behave as extremely high-gain natural amplifiers for sufficiently large local energy depositions occurring anywhere within a large fraction of their volume This observation has been used to place limits on the abundance of primordial black holes which transit thorough WD, inducing local heating by dynamical friction [57] Provided that certain minimal assumptions are met, the energy deposition rate from the Hawking process will eventually raise a sufficiently large volume of WD material above the critical temperature to trigger thermal runaway for WD in this mass range [60,61]. The authors of Ref. [61] verify that this latter process completes within ≲Gyr of BH formation in most regions of parameter space, with only some minor exceptions possible
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