Is there Supernova Evidence for Dark Energy Metamorphosis ?

We reconstruct the equation of state w(z) of dark energy (DE) using a recently released data set containing 172 type Ia supernovae without imposing any priors on w(z) (in contrast to previous studies). We find that dark energy evolves rapidly and metamorphoses from dust-like behaviour at high z ($w \simeq 0$ at $z \sim 1$) to a strongly negative equation of state at present ($w \lleq -1$ at $z \simeq 0$). Dark energy metamorphosis appears to be a robust phenomenon which manifests for a large variety of Sn data samples provided one does not invoke the weak energy prior $\rho + p \geq 0$. Invoking this prior considerably weakens the rate of growth of w(z). These results demonstrate that dark energy with an evolving equation of state provides a compelling alternative to a cosmological constant if data are analysed in a prior-free manner and the weak energy condition is not imposed by hand.