It is thought that rotation of the supernova progenitor drives a jet that accelerates material away from the explosion at close to the speed of light. In normal core collapse supernovae, 99% of neutrinos generated in the collapsing core escape without driving the ejection of material. Models for hypernova focus on the efficient transfer of energy into the ejecta. Unusually bright radio supernovae have been observed as counterparts to hypernovae, and have been termed "radio hypernovae". All supernovae associated with GRBs have shown the high-energy ejecta that characterises them as hypernovae. The total ejected mass was about 10 M ☉ and the mass of nickel ejected about 0.4 M ☉. The main absorption lines were extremely broadened and the light curve showed a very rapid brightening phase, reaching the brightness of a type Ia supernova at day 16. Its spectrum showed no hydrogen and no clear helium features, but strong silicon lines identified it as a type Ic supernova. The archetypal hypernova, SN 1998bw, was associated with GRB 980425. The electromagnetic energy released by these events varies from comparable to other type Ic supernova, to some of the most luminous supernovae known such as SN 1999as. These are typically of type Ic, and some are associated with long-duration gamma-ray bursts. The ejected nickel masses are large and the ejection velocity up to 99% of the speed of light. Hypernovae are thought to be supernovae with ejecta having a kinetic energy larger than about 10 45 joule, an order of magnitude higher than a typical core collapse supernova. Since then the term has been applied to a variety of objects, not all of which meet the standard definition for example ASASSN-15lh. Other scientists prefer to call these objects simply broad-lined type Ic supernovae. This supernova was the first to be associated with a gamma-ray burst (GRB) and it produced a shockwave containing an order of magnitude more energy than a normal supernova.
The first hypernova observed was SN 1998bw, with a luminosity 100 times higher than a standard Type Ib.
The usage of the term hypernova from the late 20th century has since been refined to refer to those supernovae with unusually large kinetic energy. That same year, hypernovae were hypothesized in greater detail by Polish astronomer Bohdan Paczyński as supernovae from rapidly spinning stars. concluded in 1998 that a hypernova was the likely cause. From analyzing the spectroscopic data for both the GRB 970508 and its host galaxy, Bloom et al. In February 1997, Dutch-Italian satellite BeppoSAX was able to trace GRB 970508 to a faint galaxy roughly 6 billion light years away. The term had previously been used to describe hypothetical explosions from diverse events such as hyperstars, extremely massive population III stars in the early universe, or from events such as black hole mergers. It referred to the extremely high energy of the explosion compared to typical core collapse supernovae. In the 1980s, the term hypernova was used to describe a theoretical type of supernova now known as a pair-instability supernova. They have also been referred to as superluminous supernovae, though that classification also includes other types of extremely luminous stellar explosions that have different origins.
Hypernovae are one of the mechanisms for producing long gamma ray bursts (GRBs), which range from 2 seconds to over a minute in duration. They usually appear similar to a type Ic supernova, but with unusually broad spectral lines indicating an extremely high expansion velocity. It is a type of stellar explosion that ejects material with an unusually high kinetic energy, an order of magnitude higher than most supernovae, with a luminosity at least 10 times greater. In this case, a massive star (>30 solar masses) collapses to form a rotating black hole emitting twin energetic jets and surrounded by an accretion disk. ESO image of hypernova SN 1998bw in a spiral arm of galaxy ESO 184-G82Ī hypernova (sometimes called a collapsar) is a very energetic supernova thought to result from an extreme core-collapse scenario.
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