A wide variety of causes have been proposed to explain events that are an order of magnitude or more greater than standard supernovae. The collapsar and CSM (circumstellar material) models are generally accepted and a number of events are well-observed. Other models are still only tentatively accepted or remain entirely theoretical.
Collapsar model . It is classified as a
Type Ic supernova due to its distinctive
spectral properties in the
radio spectrum, indicating the presence of relativistic matter.
Circumstellar material model Almost all observed SLSNe have had spectra similar to either a Type Ic or Type IIn supernova. The Type Ic SLSNe are thought to be produced by jets from fallback to a black hole, but Type IIn SLSNe have significantly different light curves and are not associated with gamma-ray bursts. Type IIn supernovae are all embedded in a dense nebula probably expelled from the progenitor star itself, and this circumstellar material (CSM) is thought to be the cause of the extra luminosity. When material expelled in an initial normal supernova explosion meets dense nebular material or dust close to the star, the shockwave converts kinetic energy efficiently into visible radiation. This effect greatly enhances these extended duration and extremely luminous supernovae, even though the initial explosive energy was the same as that of normal supernovae. Although any supernova type could potentially produce Type IIn SLSNe, theoretical constraints on the surrounding CSM sizes and densities do suggest that it will almost always be produced from the central progenitor star itself immediately prior to the observed supernova event. Such stars are likely candidates of
hypergiants or
LBVs that appear to be undergoing substantial
mass loss, due to
Eddington instability, for example,
SN2005gl.
Pair-instability supernova Another type of suspected SLSN is a
pair-instability supernova, of which
SN 2006gy may possibly be the first observed example. This supernova event was observed in a galaxy about 238 million light years (73
megaparsecs) from Earth. The theoretical basis for pair-instability collapse has been known for many decades and was suggested as a dominant source of higher mass elements in the early universe as super-massive
population III stars exploded. In a pair-instability supernova, the
pair production effect causes a sudden pressure drop in the star's core, leading to a rapid partial collapse.
Gravitational potential energy from the collapse causes runaway fusion of the core which entirely disrupts the star, leaving no remnant. Models show that this phenomenon only happens in stars with extremely low metallicity and masses between about 130 and 260 times the Sun, making them extremely unlikely in the local universe. Although originally expected to produce SLSN explosions hundreds of times greater than a normal supernova, current models predict that they actually produce luminosities ranging from about the same as a normal core collapse supernova to perhaps 50 times brighter, although remaining bright for much longer.
Magnetar energy release Models of the creation and subsequent spin-down of a
magnetar yield much higher luminosities than regular supernova events and match the observed properties of at least some SLSNe. In cases where pair-instability supernova may not be a good fit for explaining a SLSN, a magnetar explanation is more plausible.
Other models There are still models for SLSN explosions produced from binary systems, white dwarf or neutron stars in unusual arrangements or undergoing mergers, and some of these are proposed to account for some observed gamma-ray bursts. ==See also==