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Scientists have described two distinct types of supernovas. In a Type I supernova, a white dwarf star pulls material off a companion star until a runaway nuclear reaction ignites; the white dwarf is blown apart, sending debris hurtling through space. Kepler’s was a Type I. In a Type II supernova, sometimes called a core-collapse supernova, a star exhausts its nuclear fuel supply and collapses under its own gravity; the collapse then “bounces,” triggering an explosion. Could a nearby supernova pose a threat to life on Earth? Yes, in theory—but the blast would have to be very close, and at the moment no such nearby stars are at risk of exploding. Which is a good thing, because the blast of radiation from a nearby supernova would be devastating. Over a period of weeks, the supernova would emit ultraviolet rays, X-rays and gamma rays, which wouldn’t necessarily reach the ground, but would still wreak havoc on the Earth’s protective ozone layer, explains Fields. “So it wouldn’t turn us into the Hulk—but it would strip the ozone layer off the stratosphere,” he says. Without the ozone layer, the Earth would be awash in deadly ultraviolet radiation from the sun; this could wipe out phytoplankton in the oceans, with the effects working their way up the food chain, possibly leading to a mass extinction, Fields says. A supernova is a star that has reached the end of its life and has exploded. The light from a supernova can be seen from billions of light years away and is so bright that it can outshine an entire galaxy. Supernovae are important because they help create new elements and distribute them throughout the universe. Large numbers of supernovae have been catalogued and classified to provide distance candles and test models. [157] [158] Average characteristics vary somewhat with distance and type of host galaxy, but can broadly be specified for each supernova type. For other uses, see Supernova (disambiguation). SN 1994D (bright spot on the lower left), a type Ia supernova within its host galaxy, NGC 4526

A second model for the formation of type Ia supernovae involves the merger of two white dwarf stars, with the combined mass momentarily exceeding the Chandrasekhar limit. [88] This is sometimes referred to as the double-degenerate model, as both stars are degenerate white dwarfs. Due to the possible combinations of mass and chemical composition of the pair there is much variation in this type of event, [89] and, in many cases, there may be no supernova at all, in which case they will have a less luminous light curve than the more normal SN type Ia. [90] Non-standard Type Ia [ edit ]A supernova occurs when there is a change in the core of a star, one much bigger than our sun. These changes can occur in two different ways, both of which result in a supernova. With that observation, they became the first astronomers to catch a star in the act of exploding. The new supernova was named SN 2008D. Further study has shown that the supernova had some unusual properties. This stunning view of M101, also known as the Pinwheel galaxy, is one of the largest images Hubble has ever captured of a spiral galaxy, assembled from 51 exposures taken during various studies over nearly ten years. Ground-based images were used to fill in the portions of the galaxy that Hubble did not observe. (Image credit: Hubble Image: NASA, ESA, K. Kuntz (JHU), F. Bresolin (University of Hawaii), J. Trauger (Jet Propulsion Lab), J. Mould (NOAO), Y.-H. Chu (University of Illinois, Urbana) and STScI; CFHT Image: Canada-France-Hawaii Telescope/J.-C. Cuillandre/Coelum; NOAO Image: G. Jacoby, B. Bohannan, M. Hanna/NOAO/AURA/NSF) Supernovae that do not fit into the normal classifications are designated peculiar, or "pec". [61] Types III, IV, and V [ edit ] Compared to a star's entire history, the visual appearance of a supernova is very brief, sometimes spanning several months, so that the chances of observing one with the naked eye is roughly once in a lifetime. Only a tiny fraction of the 100billion stars in a typical galaxy have the capacity to become a supernova, being restricted to those having high mass and rare kinds of binary stars containing white dwarfs. [3] Early discoveries [ edit ]

A later video appeared to show Argamani being held captive in a room with a tiled floor, sipping from a bottle of water. Let's look at the more exciting Type II first. For a star to explode as a Type II supernova, it must be several times more massive than the sun (estimates run from eight to 15 solar masses). Like the sun, it will eventually run out of hydrogen and then helium fuel at its core. However, it will have enough mass and pressure to fuse carbon.This Chandra X-ray photograph shows Cassiopeia A (Cas A, for short), the youngest supernova remnant in the Milky Way. (Image credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.) Type I supernovas