Maximum Elastic Deformations of Compact Stars with Exotic Equations of State

Abstract

I make the first estimates of maximum elastic quadrupole deformations sustainable by alternatives to conventional neutron stars. Solid strange quark stars might sustain maximum ellipticities (dimensionless quadrupoles) up to a few times ${10}^{\ensuremath{-}4}$ rather than a few times ${10}^{\ensuremath{-}7}$ for conventional neutron stars, and hybrid quark-baryon or meson-condensate stars might sustain up to ${10}^{\ensuremath{-}5}$. Most of the difference is due to the shear modulus, which can be up to ${10}^{33}\text{ }\text{ }\mathrm{erg}/{\mathrm{cm}}^{3}$ rather than ${10}^{30}\text{ }\text{ }\mathrm{erg}/{\mathrm{cm}}^{3}$ in the inner crust of a conventional neutron star. Maximum solid strange star ellipticities are comparable to upper limits obtained for several known pulsars in a recent gravitational-wave search by LIGO. Maximum ellipticities of the more robust hybrid model will be detectable by LIGO at initial design sensitivity. A large shear modulus also strengthens the case for starquakes as an explanation for frequent pulsar glitches.