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A hypernova (pl. hypernovae or hypernovas) is a type of star explosion with an energy substantially higher than that of standard supernovae. An alternative term for most hypernova is "superluminous supernova" (SLSN). Such explosions are thought to be the origin of long-duration gamma-ray bursts. Just like supernovae in general, hypernovae are produced by several different types of stellar explosion: some well modelled and observed in recent years, some still tentatively suggested for observed hypernovae, and some entirely theoretical. Numerous hypernovae have been observed corresponding to supernovae type Ic and type IIn, and possibly also at least one of type IIb. The word ''collapsar'', short for ''collapsed star,'' was formerly used to refer to the end product of stellar gravitational collapse, a stellar-mass black hole. The word is now sometimes used to refer to a specific model for the collapse of a fast-rotating star, as discussed below. ==History of the term== Before the 1990s, the term "hypernova" was used sporadically to describe the theoretical extremely energetic explosions of extremely massive population III stars. It has also been used to describe other extreme energy events, such as mergers of supermassive black holes. In 1998, a paper suggesting a link between gamma-ray bursts and young massive stars formally proposed to use the term "hypernova" for the visible after-glow from those gamma-ray bursts. The energy of such events was speculated to be up to several hundred times that of known supernovae. Almost simultaneously, various over-luminous supernovae were being discovered and investigated. These events were described as hypernovae and varied from less than five to around 50 times as energetic as other supernovae and up to 20 times as luminous as a standard type Ia supernova at its peak. This definition has become standard for the term "hypernova", although not all of them are associated with gamma-ray bursts. Investigation of these types of luminous supernovae suggests that some of them are due to explosions of extremely massive low metallicity stars by the pair instability mechanism, although not with the energies that were speculated for them decades earlier. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hypernova」の詳細全文を読む スポンサード リンク
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