Awaking the Vacuum in Relativistic Stars

Void of any inherent structure in classical physics, the vacuum has revealed to be incredibly crowded with all sorts of processes in relativistic quantum physics. Yet, its direct effects are usually so subtle that its structure remains almost as evasive as in classical physics. Here, in contrast, we report on the discovery of a novel effect according to which the vacuum is compelled to play an unexpected central role in an astrophysical context. We show that the formation of relativistic stars may lead the vacuum energy density of a quantum field to an exponential growth. The vacuum-driven evolution which would then follow may lead to unexpected implications for astrophysics, while the observation of stable neutron-star configurations may teach us much on the field content of our Universe.

Figure 1

Diagram showing the values of the ratio $M/R_s$ of uniform-density compact objects which trigger the exponential growth of the vacuum energy density of massless scalar fields with coupling $\xi$ (dark-gray region). The vertical dashed line indicates the conformal-coupling value $\xi =1/6$. The black region represents the values of $M/R_s$ for which no equilibrium can be classically obtained.

Figure 2

Same as diagram in Fig. 1 but now for compact objects with parabolic density profile. The light-gray region represents values of $M/R_s$ for which equilibrium configurations are classically unstable for most realistic equations of state (see, e.g., Ref. 15).