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A supernova (PL: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months.



The last supernova directly observed in the Milky Way was Kepler's Supernova in 1604, appearing not long after Tycho's Supernova in 1572, both of which were visible to the naked eye. The remnants of more recent supernovae have been found, and observations of supernovae in other galaxies suggest they occur in the Milky Way on average about three times every century. A supernova in the Milky Way would almost certainly be observable through modern astronomical telescopes. The most recent naked-eye supernova was SN 1987A, which was the explosion of a blue supergiant star in the Large Magellanic Cloud, a satellite of the Milky Way.

Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a white dwarf, or the sudden gravitational collapse of a massive star's core.

Supernovae can expel several solar masses of material at velocities up to several percent of the speed of light. This drives an expanding shock wave into the surrounding interstellar medium, sweeping up an expanding shell of gas and dust observed as a supernova remnant. Supernovae are a major source of elements in the interstellar medium from oxygen to rubidium. The expanding shock waves of supernovae can trigger the formation of new stars. Supernovae are a major source of cosmic rays. They might also produce gravitational waves, though thus far gravitational waves have been detected only from the mergers of black holes and neutron stars.

The word supernova has the plural form supernovae /-viː/ or supernovas and is often abbreviated as SN or SNe. It is derived from the Latin word nova, meaning "new", which refers to what appears to be a temporary new bright star. Adding the prefix "super-" distinguishes supernovae from ordinary novae, which are far less luminous. The word supernova was coined by Walter Baade and Fritz Zwicky, who began using it in astrophysics lectures in 1931.[1] Its first use in a journal article came the following year in a publication by Knut Lundmark, who may have coined it independently.[2]

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 100 billion 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]

The earliest possible recorded supernova, known as HB9, could have been viewed by unknown prehistoric people of the Indian subcontinent, then recorded on a rock carving found in Burzahama region in Kashmir, dated to 45001000 BC.[4] Later, SN 185 was documented by Chinese astronomers in 185 AD. The brightest recorded supernova was SN 1006, which occurred in 1006 AD in the constellation of Lupus. This event was described by observers across China, Japan, Iraq, Egypt, and Europe.[5][6][7] The widely observed supernova SN 1054 produced the Crab Nebula.[8]

Supernovae SN 1572 and SN 1604, the latest to be observed with the naked eye in the Milky Way galaxy, had a notable influence on the development of astronomy in Europe because they were used to argue against the Aristotelian idea that the universe beyond the Moon and planets was static and unchanging.[9] Johannes Kepler began observing SN 1604 at its peak on 17 October 1604, and continued to make estimates of its brightness until it faded from naked eye view a year later.[10] It was the second supernova to be observed in a generation, after SN 1572 seen by Tycho Brahe in Cassiopeia.[11]

There is some evidence that the youngest galactic supernova, G1.9+0.3, occurred in the late 19th century, considerably more recently than Cassiopeia A from around 1680.[12] Neither supernova was noted at the time. In the case of G1.9+0.3, high extinction from dust along the plane of our galaxy could have dimmed the event sufficiently for it to go unnoticed. The situation for Cassiopeia A is less clear; infrared light echos have been detected showing that it was not in a region of especially high extinction.[13]

With the development of the astronomical telescope, observation and discovery of fainter and more distant supernovae became possible. The first such observation was of SN 1885A in the Andromeda Galaxy. A second supernova, SN 1895B, was discovered in NGC 5253 a decade later.[22] Early work on what was originally believed to be simply a new category of novae was performed during the 1920s. These were variously called "upper-class Novae", "Hauptnovae", or "giant novae".[23] The name "supernovae" is thought to have been coined by Walter Baade and Zwicky in lectures at Caltech during 1931. It was used, as "super-Novae", in a journal paper published by Knut Lundmark in 1933,[24] and in a 1934 paper by Baade and Zwicky.[25] By 1938, the hyphen had been lost and the modern name was in use.[26]

American astronomers Rudolph Minkowski and Fritz Zwicky developed the modern supernova classification scheme beginning in 1941.[27] During the 1960s, astronomers found that the maximum intensities of supernovae could be used as standard candles, hence indicators of astronomical distances.[28] Some of the most distant supernovae observed in 2003 appeared dimmer than expected. This supports the view that the expansion of the universe is accelerating.[29] Techniques were developed for reconstructing supernovae events that have no written records of being observed. The date of the Cassiopeia A supernova event was determined from light echoes off nebulae,[30] while the age of supernova remnant RX J0852.0-4622 was estimated from temperature measurements[31] and the gamma ray emissions from the radioactive decay of titanium-44.[32]

SN 2013fs was recorded three hours after the supernova event on 6 October 2013, by the Intermediate Palomar Transient Factory. This is among the earliest a supernova has been caught after detonation, and it is the earliest for which spectra have been obtained, beginning at six hours after the actual explosion. The star is located in a spiral galaxy named NGC 7610, 160 million light-years away in the constellation of Pegasus.[36][37]

The supernova SN 2016gkg was detected by amateur astronomer Victor Buso from Rosario, Argentina, on 20 September 2016.[38][39] It was the first time that the initial "shock breakout" from an optical supernova had been observed.[38] The progenitor star has been identified in Hubble Space Telescope images from before its collapse. Astronomer Alex Filippenko noted: "Observations of stars in the first moments they begin exploding provide information that cannot be directly obtained in any other way."[38]

Because supernovae are relatively rare events within a galaxy, occurring about three times a century in the Milky Way,[40] obtaining a good sample of supernovae to study requires regular monitoring of many galaxies. Today, amateur and professional astronomers are finding several hundred every year, some when near maximum brightness, others on old astronomical photographs or plates. Supernovae in other galaxies cannot be predicted with any meaningful accuracy. Normally, when they are discovered, they are already in progress.[41] To use supernovae as standard candles for measuring distance, observation of their peak luminosity is required. 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.[42]

Toward 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 professional installations such as the Katzman Automatic Imaging Telescope.[43] The Supernova Early Warning System (SNEWS) project uses a network of neutrino detectors to give early warning of a supernova in the Milky Way galaxy.[44][45] Neutrinos are particles that are produced in great quantities by a supernova, and they are not significantly absorbed by the interstellar gas and dust of the galactic disk.[46]

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. Supernova spectroscopy, used to study the physics and environments of supernovae, is more practical at low than at high redshift.[48][49] Low redshift observations also anchor the low-distance end of the Hubble curve, which is a plot of distance versus redshift for visible galaxies.[50][51]

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 that supernova.[52] The name is formed from the prefix SN, followed by the year of discovery, suffixed with a one or two-letter designation. The first 26 supernovae of the year are designated with a capital letter from A to Z. Afterward pairs of lower-case letters are used: aa, ab, and so on. Hence, for example, SN 2003C designates the third supernova reported in the year 2003.[53] The last supernova of 2005, SN 2005nc, was the 367th (14 26 + 3 = 367). Since 2000, professional and amateur astronomers have been finding several hundred supernovae each year (572 in 2007, 261 in 2008, 390 in 2009; 231 in 2013).[54][55] 041b061a72

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