A hypernova (sometimes called a collapsar) is a very energetic supernova thought to result from an extreme core-collapse scenario. 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 . 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. They usually appear similar to a type Ic supernova , but with unusually broad spectral lines indicating an extremely high expansion velocity. Hypernovae are one of the mechanisms for producing long gamma ray bursts(GRB's), which range from 2 seconds to over a minute in duration. They have also been referred to as superluminous supernova, though that classification also includes other types of extremely luminous stellar explosions that have different origins.
The term hypernova was used to describe a theoretical type of supernova now known as a pair-instability supernova. It referred to the extremely high energy of the explosion compared to typical core collapse supernova. 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.
ESO image of hypernova SN 1998bw in a spiral arm of galaxy ESO 184-G82
Hypernovae are now widely accepted to be supernovae with ejecta having a kinetic energy larger than about 1045 joule, an order of magnitude higher than a typical core collapse supernova. The ejected nickel masses are large and the ejection velocity up to 99% of the speed of light. These are typically of type Ic, and some are associated with long-duration gamma-ray bursts. The electromagetic 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.
Comments
Post a Comment