Multiwavelength X-ray, infrared, and optical compilation image of Kepler's Supernova Remnant, SN 1604. (Chandra X-ray Observatory)

A supernova (plural: supernovae or supernovas) is a stellar explosion. They are extremely luminous and cause a burst of radiation that may briefly outshine an entire galaxy before fading from view over several weeks or months. During this short interval, a supernova can radiate as much energy as the Sun could emit over its life span.^[1] The explosion expels much or all of a star's material^[2] at a velocity of up to a tenth the speed of light, driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant. Look up supernova in Wiktionary, the free dictionary. ... Download high resolution version (750x750, 53 KB)Remnants of Keplers Supernova (SN 1604). ... Download high resolution version (750x750, 53 KB)Remnants of Keplers Supernova (SN 1604). ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... For other uses, see Infrared (disambiguation). ... See also list of optical topics. ... Kepler redirects here. ... Remnant of Keplers Supernova, SN 1604 Remnant of Tychos Nova, SN 1572 A supernova remnant (SNR) is the structure resulting from the gigantic explosion of a star in a supernova. ... Supernova 1604, also known as Keplers Supernova or Keplers Star, was a supernova in the Milky Way, in the constellation Ophiuchus. ... The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. ... For other uses, see Astronomy (disambiguation). ... For other uses, see Galaxy (disambiguation). ... For other uses, see Radiation (disambiguation). ... Sol redirects here. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... Introduction The shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... Remnant of Keplers Supernova, SN 1604 Remnant of Tychos Nova, SN 1572 A supernova remnant (SNR) is the structure resulting from the gigantic explosion of a star in a supernova. ...

Several types of supernovae exist that may be triggered in one of two ways, involving either turning off or suddenly turning on the production of energy through nuclear fusion. After the core of an aging massive star ceases to generate energy from nuclear fusion, it may undergo sudden gravitational collapse into a neutron star or black hole, releasing gravitational potential energy that heats and expels the star's outer layers. Alternatively, a white dwarf star may accumulate sufficient material from a stellar companion (usually through accretion, rarely via a merger) to raise its core temperature enough to ignite carbon fusion, at which point it undergoes runaway nuclear fusion, completely disrupting it. Stellar cores whose furnaces have permanently gone out collapse when their masses exceed the Chandrasekhar limit, while accreting white dwarfs ignite as they approach this limit (roughly 1.38^[3] times the mass of the Sun). White dwarfs are also subject to a different, much smaller type of thermonuclear explosion fueled by hydrogen on their surfaces called a nova. Solitary stars with a mass below approximately nine^[4] solar masses, such as the Sun itself, evolve into white dwarfs without ever becoming supernovae. The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ... Projected timeline of the Suns life In astronomy, stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. ... This article is about the astronomical object. ... This article or section does not cite its references or sources. ... For the story by Larry Niven, see Neutron Star (story). ... For other uses, see Black hole (disambiguation). ... Potential energy can be thought of as energy stored within a physical system. ... This article or section does not adequately cite its references or sources. ... For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... In astrophysics, the term accretion is used for at least two distinct processes. ... Carbon detonation is a violent re-ignition of thermonuclear fusion in a dead star, which produces Type Ia supernovae. ... The carbon burning process is a nuclear fusion reaction that occurs in massive stars (at least 4 MSun at birth) that have used up the lighter elements in their cores. ... This article is about Thermal runaway. ... The Chandrasekhar limit (named after the Indian astrophysicist Subrahmanyan Chandrasekhar) is the maximum nonrotating mass which can be supported against gravitational collapse by electron degeneracy pressure. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... This article does not cite its references or sources. ... Artists conception of a white dwarf star accreting hydrogen from a larger companion A nova (pl. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

On average, supernovae occur about once every 50 years in a galaxy the size of the Milky Way^[5] and play a significant role in enriching the interstellar medium with heavy elements. Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars.^[6] For other uses, see Milky Way (disambiguation). ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is distinguished by its atomic number; that is, by the number of protons in its nucleus. ...

Nova (plural novae) means "new" in Latin, referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super-" distinguishes supernovae from ordinary novae, which also involve a star increasing in brightness, though to a lesser extent and through a different mechanism. According to Merriam-Webster's Collegiate Dictionary, the word supernova was first used in print in 1926. Latin was the language originally spoken in the region around Rome called Latium. ... The celestial sphere is divided by the celestial equator. ... In linguistics, a prefix is a type of affix that precedes the morphemes to which it can attach. ... Artists conception of a white dwarf star accreting hydrogen from a larger companion A nova (pl. ... 1888 advertisement for Websters Dictionary Websters Dictionary is the common title given to English language dictionaries in the United States, derived from American lexicographer Noah Webster. ...

Observation history

Main article: History of supernova observation

The Crab Nebula is a pulsar wind nebula associated with the 1054 supernova.

The earliest recorded supernova, SN 185, was viewed by Chinese astronomers in 185 CE. The widely observed supernova SN 1054 produced the Crab Nebula. Supernovae SN 1572 and SN 1604, the last to be observed in the Milky Way galaxy, had notable effects on the development of astronomy in Europe because they were used to argue against the Aristotelian idea that the world beyond the Moon and planets was immutable.^[7] The Crab Nebula is a pulsar wind nebula associated with the 1054 supernova. ... Image File history File linksMetadata Download high resolution version (2224x2212, 3149 KB) Summary Image: A Giant Hubble Mosaic of the Crab Nebula Source: http://hubblesite. ... Image File history File linksMetadata Download high resolution version (2224x2212, 3149 KB) Summary Image: A Giant Hubble Mosaic of the Crab Nebula Source: http://hubblesite. ... The Crab Nebula (catalogue designations M 1, NGC 1952, Taurus A) is a supernova remnant in the constellation of Taurus. ... A pulsar wind nebula (also known as a plerion, Greek for full) is a synchrotron nebula powered by the relativistic wind of an energetic pulsar. ... SN 1054 was a supernova that was widely seen on Earth in the year 1054. ... SN 185 is a supernova event that occured in the year 185 CE in the constellation Centaurus. ... Galileo is often referred to as the Father of Modern Astronomy. ... For other uses, see number 185. ... SN 1054 was a supernova that was widely seen on Earth in the year 1054. ... The Crab Nebula (catalogue designations M 1, NGC 1952, Taurus A) is a supernova remnant in the constellation of Taurus. ... X-ray image of the expanding cloud of debris and high energy electrons from Tychos supernova. ... Supernova 1604, also known as Keplers Supernova or Keplers Star, was a supernova in the Milky Way, in the constellation Ophiuchus. ... For other uses, see Milky Way (disambiguation). ... For other uses, see Aristotle (disambiguation). ...

Since the development of the telescope, the field of supernova discovery has enlarged to other galaxies, starting with the 1885 observation of supernova S Andromedae in the Andromeda galaxy. Supernovae provide important information on cosmological distances.^[8] During the twentieth century, successful models for each type of supernova were developed, and scientists' comprehension of the role of supernovae in the star formation process is growing. This article does not cite any references or sources. ... S Andromedae (also SN 1885A) was a supernova in the Andromeda Galaxy, the only one seen in that galaxy so far by astronomers, and the first ever noted outside the Milky Way. ... The Andromeda Galaxy (IPA: , also known as Messier 31, M31, or NGC 224; older texts often called it the Great Andromeda Nebula) is a spiral galaxy approximately 2. ...

Some of the most distant supernovae recently observed appeared dimmer than expected. This has provided evidence that the expansion of the universe may be accelerating.^[9][10] The accelerating universe is the observation that the universe appears to be expanding at an accelerated rate. ...

Discovery

Because supernovae are relatively rare events, occurring about once every 50 years in a galaxy like the Milky Way,^[5] many galaxies must be monitored regularly in order to obtain a good sample of supernovae to study.

Supernovae in other galaxies cannot be predicted with any meaningful accuracy. When they are discovered, they are already in progress.^[11] Most scientific interest in supernovae—as standard candles for measuring distance, for example—require an observation of their peak luminosity. It is therefore important to discover them well before they reach their maximum. Amateur astronomers, who greatly outnumber professional astronomers, have played an important role in finding supernovae, typically by looking at some of the closer galaxies through an optical telescope and comparing them to earlier photographs. A standard candle is an astronomical object that has a known luminosity. ... It has been suggested that this article or section be merged with Skygazing. ... Eight Inch refracting telescope. ...

Towards the end of the 20th century, astronomers increasingly turned to computer-controlled telescopes and CCDs for hunting supernovae. While such systems are popular with amateurs, there are also larger installations like the Katzman Automatic Imaging Telescope.^[12] Recently, the Supernova Early Warning System (SNEWS) project has also begun using a network of neutrino detectors to give early warning of a supernova in the Milky Way galaxy.^[13][14] A neutrino is a particle that is produced in great quantities by a supernova explosion,^[15] and it is not obscured by the interstellar gas and dust of the galactic disk. A specially developed CCD used for ultraviolet imaging in a wire bonded package. ... The Katzman Automatic Imaging Telescope (KAIT) is an automated telescope used in the search for supernovae. ... The Supernova Early Warning System (SNEWS) is a network of neutrino detectors designed to give early warning to astronomers in the event of a supernova in our Milky Way galaxy. ... For other uses, see Neutrino (disambiguation). ... Helium atom (schematic) Showing two protons (red), two neutrons (green) and two electrons (yellow). ...

Supernova searches fall into two classes: those focused on relatively nearby events and those looking for explosions farther away. Because of the expansion of the universe, the distance to a remote object with a known emission spectrum can be estimated by measuring its Doppler shift (or redshift); on average, more distant objects recede with greater velocity than those nearby, and so have a higher redshift. Thus the search is split between high redshift and low redshift, with the boundary falling around a redshift range of z = 0.1–0.3^[16]—where z is a dimensionless measure of the spectrum's frequency shift. This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ... This article is about the physical phenomenon. ...

High redshift searches for supernovae usually involve the observation of supernova light curves. These are useful for standard or calibrated candles to generate Hubble diagrams and make cosmological predictions. At low redshift, supernova spectroscopy is more practical than at high redshift, and this is used to study the physics and environments of supernovae.^[17][18] Low redshift observations also anchor the low distance end of the Hubble curve, which is a plot of distance versus redshift for visible galaxies.^[19][20]

See also: Hubble's law

This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ...

Naming convention

SN 1994D in the NGC 4526 galaxy (bright spot on the lower left). Image by NASA, ESA, The Hubble Key Project Team, and The High-Z Supernova Search Team

Supernova discoveries are reported to the International Astronomical Union's Central Bureau for Astronomical Telegrams, which sends out a circular with the name it assigns to it. The name is formed by the year of discovery, immediately followed by a one or two-letter designation. The first 26 supernovae of the year get designated with an upper case letter from A to Z. Afterward, pairs of lower-case letters are used, starting with aa, ab, and so on.^[21] Professional and amateur astronomers find several hundred supernovae each year (367 in 2005, 551 in 2006 and 572 in 2007). For example, the last supernova of 2005 was SN 2005nc, indicating that it was the 367th supernova found in 2005.^[22][23] Image File history File links Download high resolution version (2608x2608, 708 KB) Beschreibung Hubble Space Telescope-Bild der Supernova 1994D (SN1994D) am Rand der Galaxie NGC 4526 (SN 1994D ist der helle Fleck unten links) Hubble Space Telescope-Bild of Supernova 1994D (SN1994D) in galaxy NGC 4526 (SN 1994D is... Image File history File links Download high resolution version (2608x2608, 708 KB) Beschreibung Hubble Space Telescope-Bild der Supernova 1994D (SN1994D) am Rand der Galaxie NGC 4526 (SN 1994D ist der helle Fleck unten links) Hubble Space Telescope-Bild of Supernova 1994D (SN1994D) in galaxy NGC 4526 (SN 1994D is... Supernova 1994D was a Type Ia supernova in the outskirts of galaxy NGC 4526. ... Supernova SN 1994D is visible in the NGC 4526 galaxy NGC 4526 is a spiral galaxy thats part of the Virgo cluster. ... For other uses, see NASA (disambiguation). ... This article is about the European Space Agency. ... IAU redirects here. ... The Central Bureau for Astronomical Telegrams (CBAT) is the official international clearing house for information relating to transient astronomical events. ...

Historical supernovae are known simply by the year they occurred: SN 185, SN 1006, SN 1054, SN 1572 (Tycho's Nova) and SN 1604 (Kepler's Star). Since 1885, the letter notation was used, even if there was only one supernova discovered that year (e.g. SN 1885A, 1907A, etc.)—this last happened with SN 1947A. The standard abbreviation "SN" is an optional prefix. SN 185 is a supernova event that occured in the year 185 CE in the constellation Centaurus. ... ... SN 1054 was a supernova that was widely seen on Earth in the year 1054. ... X-ray image of the expanding cloud of debris and high energy electrons from Tychos supernova. ... Supernova 1604, also known as Keplers Supernova or Keplers Star, was a supernova in the Milky Way, in the constellation Ophiuchus. ...

Classification

As part of the attempt to understand supernovae, astronomers have classified them according to the absorption lines of different chemical elements that appear in their spectra. The first element for a division is the presence or absence of a line caused by hydrogen. If a supernova's spectrum contains a line of hydrogen (known as the Balmer series in the visual portion of the spectrum) it is classified Type II; otherwise it is Type I. Among those types, there are subdivisions according to the presence of lines from other elements and the shape of the light curve (a graph of the supernova's apparent magnitude versus time).^[24] A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... High resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines). ... This article is about the chemistry of hydrogen. ... Two of the balmer lines (α and β) are clearly visible in this emission spectrum of a deuterium lamp. ... In astronomy, a light curve is a graph of light intensity as a function of time. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ...

The supernovae of Type II can also be sub-divided based on their spectra. While most Type II supernova show very broad emission lines which indicate expansion velocities of many thousands of kilometres per second, some have relatively narrow features. These are called Type IIn, where the "n" stands for "narrow".^[25] Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ... Not to be confused with Silicone. ... A nanometre (American spelling: nanometer, symbol nm) (Greek: νάνος, nanos, dwarf; μετρώ, metrÏŒ, count) is a unit of length in the metric system, equal to one billionth of a metre (or one millionth of a millimetre), which is the current SI base unit of length. ... Type Ib and Ic supernovae are categories of stellar explosions. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Type Ib and Ic supernovae are categories of stellar explosions. ... The expanding remnant of SN 1987A, a Type II-P supernova in the Large Magellanic Cloud. ... The expanding remnant of SN 1987A, a Type II-P supernova in the Large Magellanic Cloud. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... kilometre per second is an SI derived unit of both speed (scalar) and velocity (vector), signified by the symbol km/s or km s-1. ...

A few supernovae, such as SN 1987K and SN 1993J, appear to change types: they show lines of hydrogen at early times, but, over a period of weeks to months, become dominated by lines of helium. The term "Type IIb" is used to describe the combination of features normally associated with Types II and Ib.^[25]

Current models

Type Ia

Main article: Type Ia supernova

There are several means by which a supernova of this type can form, but they share a common underlying mechanism. If a carbon-oxygen^[a] white dwarf accreted enough matter to reach the Chandrasekhar limit of about 1.38 solar masses^[3] (for a non-rotating star), it would no longer be able to support the bulk of its plasma through electron degeneracy pressure^[27][28] and would begin to collapse. However, the current view is that this limit is not normally attained; increasing temperature and density inside the core ignite carbon fusion as the star approaches the limit (to within about 1%^[29]), before collapse is initiated.^[3] Within a few seconds, a substantial fraction of the matter in the white dwarf undergoes nuclear fusion, releasing enough energy (1–2 × 10⁴⁴ joules)^[30] to unbind the star in a supernova explosion.^[31] An outwardly expanding shock wave is generated, with matter reaching velocities on the order of 5,000–20,000 km/s, or roughly 3% of the speed of light. There is also a significant increase in luminosity, reaching an absolute magnitude of -19.3 (or 5 billion times brighter than the Sun), with little variation.^[32] Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... For other uses, see Carbon (disambiguation). ... This article is about the chemical element and its most stable form, or dioxygen. ... This article or section does not adequately cite its references or sources. ... The Chandrasekhar limit (named after the Indian astrophysicist Subrahmanyan Chandrasekhar) is the maximum nonrotating mass which can be supported against gravitational collapse by electron degeneracy pressure. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Carbon detonation is a violent re-ignition of thermonuclear fusion in a dead star, which produces Type Ia supernovae. ... The carbon burning process is a nuclear fusion reaction that occurs in massive stars (at least 4 MSun at birth) that have used up the lighter elements in their cores. ... The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... Introduction The shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ...

One model for the formation of this category of supernova is a close binary star system. The larger of the two stars is the first to evolve off the main sequence, and it expands to form a red giant.^[33] The two stars now share a common envelope, causing their mutual orbit to shrink. The giant star then sheds most of its envelope, losing mass until it can no longer continue nuclear fusion. At this point it becomes a white dwarf star, composed primarily of carbon and oxygen.^[34][35] Eventually the secondary star also evolves off the main sequence to form a red giant. Matter from the giant is accreted by the white dwarf, causing the latter to increase in mass. For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ...

Another model for the formation of a Type Ia explosion involves the merger of two white dwarf stars, with the combined mass momentarily exceeding the Chandrasekhar limit.^[36] A white dwarf could also accrete matter from other types of companions, including a main sequence star (if the orbit is sufficiently close).

Type Ia supernovae follow a characteristic light curve—the graph of luminosity as a function of time—after the explosion. This luminosity is generated by the radioactive decay of nickel-56 through cobalt-56 to iron-56.^[32] The peak luminosity of the light curve was believed to be consistent across Type Ia supernovae (the vast majority of which are initiated with a uniform mass via the accretion mechanism), allowing them to be used as a secondary^[37] standard candle to measure the distance to their host galaxies.^[38] However, recent discoveries reveal that there is some evolution in the average lightcurve width, and thus in the intrinsic luminosity of Supernovae, although significant evolution is found only over a large redshift baseline.^[39] In astronomy, a light curve is a graph of light intensity as a function of time. ... Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ... For other uses, see Nickel (disambiguation). ... For other uses, see Cobalt (disambiguation). ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... A standard candle is an astronomical object that has a known luminosity. ... For other uses, see Galaxy (disambiguation). ...

Type Ib and Ic

Main article: Type Ib and Ic supernovae

These events, like supernovae of Type II, are probably massive stars running out of fuel at their centers; however, the progenitors of Types Ib and Ic have lost most of their outer (hydrogen) envelopes due to strong stellar winds or else from interaction with a companion.^[40] Type Ib supernovae are thought to be the result of the collapse of a massive Wolf-Rayet star. There is some evidence that a few percent of the Type Ic supernovae may be the progenitors of gamma ray bursts (GRB), though it is also believed that any hydrogen-stripped, Type Ib or Ic supernova could be a GRB, dependent upon the geometry of the explosion.^[41] Type Ib and Ic supernovae are categories of stellar explosions. ... A solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star (in the case of a star other than the Earths Sun, it may be called a stellar wind instead). ... Hubble Space Telescope image of nebula M1-67 around Wolf Rayet star WR 124 Wolf-Rayet stars (often referred to as WR stars) are evolved, massive stars (over 20 solar masses), and are losing their mass rapidly by means of a very strong stellar wind, with speeds up to 2000... In astronomy, gamma-ray bursts (GRBs) are flashes of gamma rays that last from seconds to hours, the longer ones being followed by several days of X-ray afterglow. ...

Type II

Main article: Type II supernova

The onion-like layers of a massive, evolved star just prior to core collapse. (Not to scale.)

Stars with at least nine solar masses of material evolve in a complex fashion.^[4] In the core of the star, hydrogen is fused into helium and the thermal energy released creates an outward pressure, which maintains the core in hydrostatic equilibrium and prevents collapse. The expanding remnant of SN 1987A, a Type II-P supernova in the Large Magellanic Cloud. ... Image File history File links Evolved_star_fusion_shells. ... Image File history File links Evolved_star_fusion_shells. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In thermal physics, thermal energy is the energy portion of a system that increases with its temperature. ... Hydrostatic equilibrium occurs when compression due to gravity is balanced by a pressure gradient which creates a pressure gradient force in the opposite direction. ...

When the core's supply of hydrogen is exhausted, this outward pressure is no longer created. The core begins to collapse, causing a rise in temperature and pressure which becomes great enough to ignite the helium and start a helium-to-carbon fusion cycle, creating sufficient outward pressure to halt the collapse. The core expands and cools slightly, with a hydrogen-fusion outer layer, and a hotter, higher pressure, helium-fusion center. (Other elements such as magnesium, sulfur and calcium are also created and in some cases burned in these further reactions.) This article or section does not cite its references or sources. ... For other uses, see Carbon (disambiguation). ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... This article is about the chemical element. ... For other uses, see Calcium (disambiguation). ...

This process repeats several times, and each time the core collapses and the collapse is halted by the ignition of a further process involving more massive nuclei and higher temperatures and pressures. Each layer is prevented from collapse by the heat and outward pressure of the fusion process in the next layer inward; each layer also burns hotter and quicker than the previous one – the final burn of silicon to nickel consumes its fuel in around one day, or a few days.^[42] The star becomes layered like an onion, with the burning of more easily fused elements occurring in larger shells.^[43][44]

In the later stages, increasingly heavier elements undergo nuclear fusion, and the binding energy of the relevant nuclei increases. Fusion produces progressively lower levels of energy, and also at higher core energies photodisintegration and electron capture occur which cause energy loss in the core and a general acceleration of the fusion processes to maintain equilibrium.^[42] This escalation culminates with the production of nickel-56, which is unable to produce energy through fusion (but does produce iron-56 through radioactive decay).^[45] As a result, a nickel-iron core^[46] builds up that cannot produce any further outward pressure on a scale needed to support the rest of the structure. It can only support the overlaying mass of the star through the degeneracy pressure of electrons in the core. If the star is sufficiently large, then the iron-nickel core will eventually exceed the Chandrasekhar limit (1.38 solar masses), at which point this mechanism catastrophically fails. The forces holding atomic nuclei apart in the innermost layer of the core suddenly give way, the core implodes due to its own mass, and no further fusion process can ignite or prevent collapse this time.^[27] Binding energy is the energy required to disassemble a whole into separate parts. ... Photodisintegration is a physics process in which extremely high energy Gamma rays impact an atomic nucleus and cause it to break apart in a nuclear fission reaction. ... Electron capture is a decay mode for isotopes that will occur when there are too many protons in the nucleus of an atom, and there isnt enough energy to emit a positron; however, it continues to be a viable decay mode for radioactive isotopes that can decay by positron... Look up equilibrium in Wiktionary, the free dictionary. ... In astrophysics, silicon burning is a nuclear fusion reaction which occurs in massive stars. ... Degenerate matter is matter which has sufficiently high density that the dominant contribution to its pressure arises from the Pauli exclusion principle. ... For other uses, see Electron (disambiguation). ... The Chandrasekhar limit (named after the Indian astrophysicist Subrahmanyan Chandrasekhar) is the maximum nonrotating mass which can be supported against gravitational collapse by electron degeneracy pressure. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In an explosion (top), force radiates away from a source. ...

Core collapse

See also: Gravitational collapse

The core collapses in on itself with velocities reaching 70,000 km/s (0.23c),^[47] resulting in a rapid increase in temperature and density. The energy loss processes operating in the core cease to be in equilibrium. Through photodisintegration, gamma rays decompose iron into helium nuclei and free neutrons, absorbing energy, whilst electrons and protons merge via electron capture, producing neutrons and electron neutrinos which escape. This article or section does not cite its references or sources. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... Photodisintegration is a physics process in which extremely high energy Gamma rays impact an atomic nucleus and cause it to break apart in a nuclear fission reaction. ... This article is about electromagnetic radiation. ... This article or section does not adequately cite its references or sources. ... For other uses, see Electron (disambiguation). ... For other uses, see Proton (disambiguation). ... Electron capture is a decay mode for isotopes that will occur when there are too many protons in the nucleus of an atom, and there isnt enough energy to emit a positron; however, it continues to be a viable decay mode for radioactive isotopes that can decay by positron... For other uses, see Neutrino (disambiguation). ...

In a typical Type II supernova, the newly formed neutron core has an initial temperature of about 100 billion kelvins (100 GK); 6000 times the temperature of the sun's core. Much of this thermal energy must be shed for a stable neutron star to form (otherwise the neutrons would "boil away"), and this is accomplished by a further release of neutrinos.^[48] These 'thermal' neutrinos form as neutrino-antineutrino pairs of all flavors, and total several times the number of electron-capture neutrinos.^[49] About 10⁴⁶ joules of gravitational energy—about 10% of the star's rest mass—is converted into a ten-second burst of neutrinos; the main output of the event.^[42][50] These carry away energy from the core and accelerate the collapse, while some neutrinos are absorbed by the star's outer layers and begin the supernova explosion.^[51] For other uses, see Kelvin (disambiguation). ... Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. ...

The inner core eventually reaches typically 30 km diameter,^[42] and a density comparable to that of an atomic nucleus, and further collapse is abruptly stopped by strong force interactions and by degeneracy pressure of neutrons. The infalling matter, suddenly halted, rebounds, producing a shock wave that propagates outward. Computer simulations indicate that this expanding shock does not directly cause the supernova explosion;^[42] rather, it stalls within milliseconds^[52] in the outer core as energy is lost through the dissociation of heavy elements, and a process that is not clearly understood is necessary to allow the outer layers of the core to reabsorb around 10⁴⁴ joules^[b] (1 foe) of energy, producing the visible explosion.^[53] Current research focuses upon rotational and magnetic effects as the basis for this process.^[42] The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ... Degenerate matter is matter which has sufficiently high density that the dominant contribution to its pressure arises from the Pauli exclusion principle. ... Introduction The shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. ... One millisecond is one-thousandth of a second. ... A foe is a unit of energy equal to 1044 joules. ... This article is about rotation as a movement of a physical body. ... For the indie-pop band, see The Magnetic Fields. ...

Within a massive, evolved star (a) the onion-layered shells of elements undergo fusion, forming an iron core (b) that reaches Chandrasekhar-mass and starts to collapse. The inner part of the core is compressed into neutrons (c), causing infalling material to bounce (d) and form an outward-propagating shock front (red). The shock starts to stall (e), but it is re-invigorated by neutrino interaction. The surrounding material is blasted away (f), leaving only a degenerate remnant.

When the progenitor star is below about 20 solar masses (depending on the strength of the explosion and the amount of material that falls back), the degenerate remnant of a core collapse is a neutron star.^[47] Above this mass the remnant collapses to form a black hole.^[44][54] (This type of collapse is one of many candidate explanations for gamma ray bursts—producing a large burst of gamma rays through a still theoretical hypernova explosion.)^[55] The theoretical limiting mass for this type of core collapse scenario was estimated around 40–50 solar masses. Image File history File links Core_collapse_scenario. ... Image File history File links Core_collapse_scenario. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... For the story by Larry Niven, see Neutron Star (story). ... For other uses, see Black hole (disambiguation). ... The image above shows the optical afterglow of gamma ray burst GRB-990123 taken on January 23, 1999. ... This article is about electromagnetic radiation. ... This article needs additional references or sources for verification. ...

Above 50 solar masses, stars were believed to collapse directly into a black hole without forming a supernova explosion,^[56] although uncertainties in models of supernova collapse make accurate calculation of these limits difficult. In fact recent evidence has shown stars in the range of about 140–250 solar masses, with a relatively low proportion of elements more massive than helium, may be capable of forming pair-instability supernovae without leaving behind a black hole remnant. This rare type of supernova is formed by an alternate mechanism (partially analogous to that of Type Ia explosions) that does not require an iron core. An example is the Type II supernova SN 2006gy, with an estimated 150 solar masses, that demonstrated the explosion of such a massive star differed fundamentally from previous theoretical predictions.^[57][58] This illustration explains the pair-instability supernova process that astronomers think triggered the explosion in SN 2006gy. ... SN 2006gy and the core of its home galaxy, NGC 1260, viewed in x-ray light from the Chandra X-ray Observatory. ...

Light curves and unusual spectra

This graph of the luminosity (relative to the Sun) as a function of time shows the characteristic shapes of the light curves for a Type II-L and II-P supernova.

The light curves for Type II supernovae are distinguished by the presence of hydrogen Balmer absorption lines in the spectra. These light curves have an average decay rate of 0.008 magnitudes per day; much lower than the decay rate for Type I supernovae. Type II are sub-divided into two classes, depending on whether there is a plateau in their light curve (Type II-P) or a linear decay rate (Type II-L). The net decay rate is higher at 0.012 magnitudes per day for Type II-L compared to 0.0075 magnitudes per day for Type II-P. The difference in the shape of the light curves is believed to be caused, in the case of Type II-L supernovae, by the expulsion of most of the hydrogen envelope of the progenitor star.^[26] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Two of the balmer lines (α and β) are clearly visible in this emission spectrum of a deuterium lamp. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ...

The plateau phase in Type II-P supernovae is due to a change in the opacity of the exterior layer. The shock wave ionizes the hydrogen in the outer envelope, which greatly increases the opacity. This prevents photons from the inner parts of the explosion from escaping. Once the hydrogen cools sufficiently to recombine, the outer layer becomes transparent.^[59] A substance or object that is opaque is neither transparent nor translucent. ... ...

Of the Type II supernovae with unusual features in their spectra, Type IIn supernovae may be produced by the interaction of the ejecta with circumstellar material.^[60] Type IIb supernovae are likely massive stars which have lost most, but not all, of their hydrogen envelopes through tidal stripping by a companion star. As the ejecta of a Type IIb expands, the hydrogen layer quickly becomes optically thin and reveals the deeper layers.^[61] Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ...

Asymmetry

A long-standing puzzle surrounding supernovae has been a need to explain why the compact object remaining after the explosion is given a large velocity away from the core.^[62] (Neutron stars are observed, as pulsars, to have high velocities; black holes presumably do as well, but are far harder to observe in isolation.) This kick can be substantial, propelling an object of more than a solar mass at a velocity of 500 km/s or greater. This displacement is believed to be caused by an asymmetry in the explosion, but the mechanism by which this momentum is transferred to the compact object has remained a puzzle. Some explanations for this kick include convection in the collapsing star and jet production during neutron star formation. For the story by Larry Niven, see Neutron Star (story). ... It has been suggested that Radio pulsar be merged into this article or section. ... For other uses, see Black hole (disambiguation). ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

This composite image shows X-ray (blue) and optical (red) radiation from the Crab Nebula's core region. A pulsar near the center is propelling particles to almost the speed of light.^[63] This neutron star is travelling at an estimated 375 km/s.^[64] NASA/CXC/HST/ASU/J. Hester et al. image credit.

One explanation for the asymmetry in the explosion is large-scale convection above the core. The convection can create variations in the local abundances of elements, resulting in uneven nuclear burning during the collapse, bounce and resulting explosion.^[65] Image File history File links Download high-resolution version (2400x2400, 314 KB) A composite image of the Crab Nebula showing the X-ray (blue), and optical (red) images superimposed. ... Image File history File links Download high-resolution version (2400x2400, 314 KB) A composite image of the Crab Nebula showing the X-ray (blue), and optical (red) images superimposed. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... The Crab Nebula (catalogue designations M 1, NGC 1952, Taurus A) is a supernova remnant in the constellation of Taurus. ... It has been suggested that Radio pulsar be merged into this article or section. ... For other uses, see NASA (disambiguation). ...

Another explanation is that accretion of gas onto the central neutron star can create a disk that drives highly directional jets, propelling matter at a high velocity out of the star, and driving transverse shocks that completely disrupt the star. These jets might play a crucial role in the resulting supernova explosion.^[66][67] (A similar model is now favored for explaining long gamma ray bursts.) An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... In astronomy, gamma-ray bursts (GRBs) are flashes of gamma rays that last from seconds to hours, the longer ones being followed by several days of X-ray afterglow. ...

Initial asymmetries have also been confirmed in Type Ia supernova explosions through observation. This result may mean that the initial luminosity of this type of supernova may depend on the viewing angle. However, the explosion becomes more symmetrical with the passage of time. Early asymmetries are detectable by measuring the polarization of the emitted light.^[68]

Type Ia vis-à-vis core collapse

Because they have a similar functional model, Types Ib, Ic and various Types II supernovae are collectively called Core Collapse supernovae. A fundamental difference between Type Ia and Core Collapse supernovae is the source of energy for the radiation emitted near the peak of the light curve. The progenitors of Core Collapse supernovae are stars with extended envelopes that can attain a degree of transparency with a relatively small amount of expansion. Most of the energy powering the emission at peak light is derived from the shock wave that heats and ejects the envelope.^[69]

The progenitors of Type Ia supernovae, on the other hand, are compact objects, much smaller (but more massive) than the Sun, that must expand (and therefore cool) enormously before becoming transparent. Heat from the explosion is dissipated in the expansion and is not available for light production. The radiation emitted by Type Ia supernovae is thus entirely attributable to the decay of radionuclides produced in the explosion; principally nickel-56 (with a half-life of 6.1 days) and its daughter cobalt-56 (with a half-life of 77 days). Gamma rays emitted during this nuclear decay are absorbed by the ejected material, heating it to incandescence. A radionuclide is an atom with an unstable Goat, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron (see internal conversion) . The radionuclide, in this process, undergoes radioactive decay... For other uses, see Nickel (disambiguation). ... For other uses, see Cobalt (disambiguation). ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles. ... Molten glassy material glows orange with incandescence in a vitrification experiment. ...

As the material ejected by a Core Collapse supernova expands and cools, radioactive decay eventually takes over as the main energy source for light emission in this case also. A bright Type Ia supernova may expel 0.5–1.0 solar masses of nickel-56,^[70] while a Core Collapse supernova probably ejects closer to 0.1 solar mass of nickel-56.^[71] In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

Interstellar impact

Source of heavy elements

Main article: Supernova nucleosynthesis

Supernovae are a key source of elements heavier than oxygen. These elements are produced by nuclear fusion (for iron-56 and lighter elements), and by nucleosynthesis during the supernova explosion for elements heavier than iron. Supernova are the most likely, although not undisputed, candidate sites for the r-process, which is a rapid form of nucleosynthesis that occurs under conditions of high temperature and high density of neutrons. The reactions produce highly unstable nuclei that are rich in neutrons. These forms are unstable and rapidly beta decay into more stable forms. Supernova nucleosynthesis refers to the production of new chemical elements inside supernovae. ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is distinguished by its atomic number; that is, by the number of protons in its nucleus. ... This article is about the chemical element and its most stable form, or dioxygen. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons and neutrons). ... The R process (R for rapid) is a neutron capture process for radioactive elements which occurs in high neutron density, high temperature conditions. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... This article or section does not adequately cite its references or sources. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ...

The r-process reaction, which is likely to occur in type II supernovae, produces about half of all the element abundance beyond iron, including plutonium, uranium and californium.^[72] The only other major competing process for producing elements heavier than iron is the s-process in large, old red giant stars, which produces these elements much more slowly, and which cannot produce elements heavier than lead.