Do massive neutron stars end as invisible dark energy objects?
  Astronomical observations reveal a gap in the mass spectrum of relativistic objects: neither black holes nor neutron stars having masses in the range of 2 - 5$\,\MSun$ have ever been observed. Based on the solution of the TOV equation modified to include a universal scalar field $\cal{H},$ we argue that all moderate and massive neutron stars should end invisible dark energy objects (DEOs). Triggered by the $\cal{H}-$baryonic matter interaction, a phase transition from normal compressible nuclear matter into an incompressible quark-superfluid is shown to occur at roughly $3$ times the nuclear density. At the transition front, the scalar field is set to inject energy at the maximum possible rate via a non-local interaction potential $V_\phi = a_0 r^2 + b_0.$ This energy creates a global confining bag, inside which a sea of freely moving quarks is formed in line with the asymptotic freedom of quantum chromodynamics. The transition front, $r_f,$ creeps from inside-to-outside to reach the surface of the object on the scale of Gyrs or even shorter, depending on its initial compactness. Having $r_f$ reached $R_\star,$ then the total injected dark energy via $V_\phi $ turns NSs into invisible DEOs. While this may provide an explanation for the absence of stellar BHs with $M_{BH}\leq 5 \MSun$ and NSs with $M_{NS}\geq 2 \MSun$, it also suggests that DEOs might have hidden connection to dark matter and dark energy in cosmology. 
A.A. Hujeirat
astro-ph.HE