hypernova

Hypernova is an informal term used to describe a subset of core-collapse supernovae with exceptionally high explosion energies, roughly an order of magnitude greater than those of typical core-collapse events. They are often, but not always, associated with long-duration gamma-ray bursts (GRBs). The defining observational clue is unusually energetic, rapidly expanding ejecta, with kinetic energies around 10^52 ergs, far exceeding the ~10^51 ergs typical of ordinary core-collapse supernovae. These events can be extremely luminous, though the radiated energy is only a fraction of the total energy budget.

The leading theoretical framework for hypernovae is the collapsar model. In this scenario, a rapidly rotating massive star collapses to a black hole, forming an accretion disk that drives energetic relativistic jets. If such jets drill through the stellar envelope and align with Earth, a long gamma-ray burst accompanies the supernova. Even when the gamma-ray burst is not observed, the explosion can still manifest as a hypernova through its bright, high-velocity ejecta and broad spectral features.

Progenitors are typically massive stars that have lost their outer hydrogen and helium envelopes, such as Wolf–Rayet stars, producing a stripped-envelope Type Ic supernova as the underlying explosion mechanism. Notable associations include SN 1998bw with GRB 980425 and SN 2003dh with GRB 030329, which advanced the link between some hypernovae and GRBs. The term remains somewhat informal, and in modern literature many authors describe these events as very energetic Type Ic-BL supernovae rather than drawing a strict boundary.