SN 1006 was a supernova that is likely the brightest observed stellar event in recorded history, reaching an estimated −7.5 visual magnitude, and exceeding roughly sixteen times the brightness of Venus. Appearing between April 30 and May 1, 1006 AD in the constellation of Lupus, this "guest star" was described by observers across the modern day countries of China, Japan, Iraq, Egypt, and the continent of Europe, and possibly recorded in North American petroglyphs. Some reports state it was clearly visible in the daytime. Modern astronomers now consider its distance from Earth to be about 7,200 light-years.
SN 1006 supernova remnant
|Other designations||SN 1006, SN 1006A, SN 1016, SNR G327.6+14.6, SNR G327.6+14.5, 1ES 1500-41.5, MRC 1459-417|
|Spectral class||Type Ia (presumably)|
|Date||17 April 1006 to 1 May 1006|
|Right ascension||15h 2m 8s|
|Distance||7,200 light-years (2.2 kpc)|
|Colour (B-V)||Japanese observers describe as blue-white at visible spectrum|
|Notable features||Brightest supernova in recorded history, and therefore most described of the pretelescopic era|
|Peak apparent magnitude||−7.5|
|Preceded by||SN 393|
|Followed by||SN 1054|
Egyptian astrologer and astronomer Ali ibn Ridwan, writing in a commentary on Ptolemy's Tetrabiblos, stated that the "spectacle was a large circular body, 2½ to 3 times as large as Venus. The sky was shining because of its light. The intensity of its light was a little more than a quarter that of Moon light" (or perhaps "than the light of the Moon when one-quarter illuminated"). Like all other observers, Ali ibn Ridwan noted that the new star was low on the southern horizon. Some astrologers interpreted the event as a portent of plague and famine.
The most northerly sighting is recorded in the annals  of the Abbey of Saint Gall in Switzerland, at a latitude of 47.5° North. Monks at St Gall provide independent data as to its magnitude and location in the sky, writing that "[i]n a wonderful manner this was sometimes contracted, sometimes diffused, and moreover sometimes extinguished… It was seen likewise for three months in the inmost limits of the south, beyond all the constellations which are seen in the sky". This description is often taken as probable evidence that the supernova was of Type Ia.
Some sources state that the star was bright enough to cast shadows; it was certainly seen during daylight hours for some time.
According to Songshi, the official history of the Song Dynasty (sections 56 and 461), the star seen on 1 May 1006 appeared to the south of constellation Di, east of Lupus and one degree to the west of Centaurus. It shone so brightly that objects on the ground could be seen at night.
By December, it was again sighted in the constellation Di. The Chinese astrologer Zhou Keming, who was on his return to Kaifeng from his duty in Guangdong, interpreted the star to the emperor on May 30 as an auspicious star, yellow in color and brilliant in its brightness, that would bring great prosperity to the state over which it appeared. The reported color yellow should be taken with some suspicion however, because Zhou may have chosen a favorable color for political reasons.
There appear to have been two distinct phases in the early evolution of this supernova. There was first a three-month period at which it was at its brightest; after this period it diminished, then returned for a period of about eighteen months.
A petroglyph by the Hohokam in White Tank Mountain Regional Park, Arizona, has been interpreted as the first known North American representation of the supernova, though other researchers remain skeptical.
SN 1006's associated supernova remnant from this event was not identified until 1965, when Doug Milne and Frank Gardner used the Parkes radio telescope to demonstrate a connection to known radio source, PKS 1459-41. This is located near the star Beta Lupi, displaying a 30 arcmin circular shell. X-ray and optical emission from this remnant have also been detected, and during 2010 the H.E.S.S. gamma-ray observatory announced the detection of very-high-energy gamma-ray emission from the remnant. No associated neutron star or black hole has been found, which is the situation expected for the remnant of a Type Ia supernova (a class of explosion believed to completely disrupt its progenitor star). A survey in 2012 to find any surviving companions of the SN 1006 progenitor found no subgiant or giant companion stars, indicating that SN 1006 was most likely a double degenerate progenitor, that is, the merging of two white dwarf stars.
Research has suggested that Type Ia supernovae can irradiate the Earth with significant amounts of gamma-ray flux, compared with the typical flux from the Sun, up to distances on the order of 1 kiloparsec. The greatest risk is to the Earth's protective ozone layer, producing effects on life and climate. While SN 1006 did not appear to have such significant effects, a signal of its outburst can be found in nitrate deposits in Antarctic ice.
Year 1006 (MVI) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar.Ali ibn Ridwan
Abu'l Hassan Ali ibn Ridwan Al-Misri , أبو الحسن علي بن رضوان المصري (c. 988 - c. 1061) was an Arab of Egyptian origin who was a physician, astrologer and astronomer, born in Giza.
He was a commentator on ancient Greek medicine, and in particular on Galen; his commentary on Galen's Ars Parva was translated by Gerardo Cremonese. However, he is better known for providing the most detailed description of the supernova now known as SN 1006, the brightest stellar event in recorded history, which he observed in the year 1006. This was written in a commentary on Ptolemy's work Tetrabiblos.
He was later cited by European authors as Haly, or Haly Abenrudian. According to Alistair Cameron Crombie he also contributed to the theory of induction. He engaged in a celebrated polemic against another physician, Ibn Butlan of Baghdad.Beta Lupi
Beta Lupi (β Lupi, β Lup), or Kekouan , is a star in the southern constellation of Lupus. It has an apparent visual magnitude of 2.7, making it readily visible to the naked eye. Based upon parallax measurements, this star is located at a distance of about 383 light-years (117 parsecs) from Earth.Egyptian astronomy
Egyptian astronomy begins in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments. By the time the historical Dynastic Period began in the 3rd millennium BCE, the 365-day period of the Egyptian calendar was already in use, and the observation of stars was important in determining the annual flooding of the Nile.
The Egyptian pyramids were carefully aligned towards the pole star, and the temple of Amun-Re at Karnak was aligned on the rising of the midwinter Sun. Astronomy played a considerable part in fixing the dates of religious festivals and determining the hours of night, and temple astrologers were especially adept at watching the stars and observing the conjunctions and risings of the Sun, Moon, and planets, as well as the lunar phases.
In Ptolemaic Egypt, the Egyptian tradition merged with Greek astronomy and Babylonian astronomy, with the city of Alexandria in Lower Egypt becoming the centre of scientific activity across the Hellenistic world. Roman Egypt produced the greatest astronomer of the era, Ptolemy (90–168 CE). His works on astronomy, including the Almagest, became the most influential books in the history of Western astronomy. Following the Muslim conquest of Egypt, the region came to be dominated by Arabic culture and Islamic astronomy.
The astronomer Ibn Yunus (c. 950–1009) observed the Sun's position for many years using a large astrolabe, and his observations on eclipses were still used centuries later. In 1006, Ali ibn Ridwan observed the SN 1006, a supernova regarded as the brightest stellar event in recorded history, and left the most detailed description of it. In the 14th century, Najm al-Din al-Misri wrote a treatise describing over 100 different types of scientific and astronomical instruments, many of which he invented himself.Evaporating gaseous globule
An evaporating gas globule or EGG is a region of hydrogen gas in outer space approximately 100 astronomical units in size, such that gases shaded by it are shielded from ionizing UV rays. Dense areas of gas shielded by an evaporating gas globule can be conducive to the birth of stars. Evaporating gas globules were first conclusively identified via photographs taken by the Hubble Space Telescope in 1995.EGG's are the likely predecessors of new protostars. Inside an EGG the gas and dust are denser than in the surrounding dust cloud. Gravity pulls the cloud even more tightly together as the EGG continues to draw in material from its surroundings. As the cloud density builds up the globule becomes hotter under the weight of the outer layers, a protostar is formed inside the EGG.
A protostar may have too little mass to become a star. If so it becomes a brown dwarf. If the protostar has sufficient mass, the density reaches a critical level where the temperature exceeds 10 million kelvin at its center. At this point, a nuclear reaction starts converting hydrogen to helium and releasing large amounts of energy. The protostar then becomes a star and joins the main sequence on the HR diagram.Frank Winkler
P. Frank Winkler, Jr. is an astronomer and noted subject-matter expert on supernova. He received his doctorate from Harvard and is currently the Gamaliel Painter Bicentennial Professor in Physics at Middlebury College located in Middlebury, Vermont.Dr. Winkler has calculated the distance for the brightest supernova event recorded in human history, SN 1006, as being ~7,200 light years distant.
Winkler is also the recipient of record for a Recovery Act grant for continued research regarding supernova. Frank Winkler is also a member of the International Astronomical Union.List of supernova remnants
This is a list of observed supernova remnants.List of supernovae
This is a list of supernovae that are of historical significance. These include supernovae that were observed prior to the availability of photography, and individual events that have been the subject of a scientific paper that contributed to supernova theory.Lupus (constellation)
Lupus is a constellation located in the deep Southern Sky. Its name is Latin for wolf. Lupus was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations, although it was previously an asterism associated with the neighboring constellation Centaurus.Magnitude (astronomy)
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus.
The scale is logarithmic and defined such that each step of one magnitude changes the brightness by a factor of the fifth root of 100, or approximately 2.512. For example, a magnitude 1 star is exactly 100 times brighter than a magnitude 6 star. The brighter an object appears, the lower the value of its magnitude, with the brightest objects reaching negative values.
Astronomers use two different definitions of magnitude: apparent magnitude and absolute magnitude. The apparent magnitude (m) is the brightness of an object as it appears in the night sky from Earth. Apparent magnitude depends on an object's intrinsic luminosity, its distance, and the extinction reducing its brightness. The absolute magnitude (M) describes the intrinsic luminosity emitted by an object and is defined to be equal to the apparent magnitude that the object would have if it were placed at a certain distance from Earth, 10 parsecs for stars. A more complex definition of absolute magnitude is used for planets and small Solar System bodies, based on its brightness at one astronomical unit from the observer and the Sun.
The Sun has an apparent magnitude of −27 and Sirius, the brightest visible star in the night sky, −1.46. Apparent magnitudes can also be assigned to artificial objects in Earth orbit with the International Space Station (ISS) sometimes reaching a magnitude of −6.SN 1054
SN 1054 is a supernova that was first observed on 4 July 1054, and remained visible for around two years.
The event was recorded in contemporary Chinese astronomy, and references to it are also found in a later (13th-century) Japanese document, and in a document from the Arab world. Furthermore, there are a number of proposed, but doubtful, references from European sources recorded in the 15th century, and perhaps a pictograph associated with the Ancestral Puebloan culture found near the Peñasco Blanco site in New Mexico.
The remnant of SN 1054, which consists of debris ejected during the explosion, is known as the Crab Nebula. It is located in the sky near the star Zeta Tauri (ζ Tauri). The core of the exploding star formed a pulsar, called the Crab Pulsar (or PSR B0531+21). The nebula and the pulsar that it contains are some of the most studied astronomical objects outside the Solar System. It is one of the few Galactic supernovae where the date of the explosion is well known. The two objects are the most luminous in their respective categories. For these reasons, and because of the important role it has repeatedly played in the modern era, SN 1054 is the best known supernova in the history of astronomy.
The Crab Nebula is easily observed by amateur astronomers thanks to its brightness, and was also catalogued early on by professional astronomers, long before its true nature was understood and identified. When the French astronomer Charles Messier watched for the return of Halley's Comet in 1758, he confused the nebula for the comet, as he was unaware of the former's existence. Motivated by this error, he created his catalogue of non-cometary nebulous objects, the Messier Catalogue, to avoid such mistakes in the future. The nebula is catalogued as the first Messier object, or M1.SN 393
SN 393 is the modern designation for a probable supernova that was reported by the Chinese in the year 393 CE. An extracted record of this astronomical event was translated into English as follows:
A guest star appeared within the asterism Wěi during the second lunar month of the 18th year of the Tai-Yuan reign period, and disappeared during the ninth lunar month.
The second lunar month mentioned in the record corresponds to the period 27 February to 28 March 393 CE, while the ninth lunar month ran from 22 October to 19 November 393 CE. The bowl-shaped asterism named Wěi is formed by the tail of the modern constellation Scorpius. This asterism consists of the stars in Scorpius designated ε, μ, ζ, η, θ, ι, κ, λ and ν. The guest star reached an estimated apparent magnitude of −1 and was visible for about eight months before fading from sight, whose lengthy duration suggests the source was a supernova.Stellar collision
A stellar collision is the coming together of two stars caused by stellar dynamics within a star cluster, or by the orbital decay of a binary star due to stellar mass loss or gravitational radiation, or by other mechanisms not yet well understood.
Astronomers predict that events of this type occur in the globular clusters of our galaxy about once every 10,000 years. On 2 September 2008 scientists first observed a stellar merger in Scorpius (named V1309 Scorpii), though it was not known to be the result of a stellar merger at the time. A series of stellar collisions in a dense cluster over a short period of time can lead to an intermediate-mass black hole via "runaway stellar collisions".Any stars in the universe can collide, whether they are 'alive', meaning fusion is still active in the star, or 'dead', with fusion no longer taking place. White dwarf stars, neutron stars, black holes, main sequence stars, giant stars, and supergiants are very different in type, mass, temperature, and radius, and so react differently.A gravitational wave event that occurred on 25 August 2017, GW170817, was reported on 16 October 2017 to be associated with the merger of two neutron stars in a distant galaxy, the first such merger to be observed via gravitational radiation.Supernova
A supernova ( plural: supernovae or supernovas, abbreviations: SN and SNe) is a transient astronomical event that occurs during the last stellar evolutionary stages of the life of a massive star, whose dramatic and catastrophic destruction is marked by one final, titanic explosion. This causes the sudden appearance of a "new" bright star, before slowly fading from sight over several weeks or months or years.
Supernovae are more energetic than novae. In Latin, nova means "new", referring astronomically 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 in 1931.
Only three Milky Way, naked-eye supernova events have been observed during the last thousand years, though many have been observed in other galaxies. The most recent directly observed supernova in the Milky Way was Kepler's Supernova in 1604, but the remnants of recent supernovae have also been found. Observations of supernovae in other galaxies suggest they occur on average about three times every century in the Milky Way, and that any galactic supernova would almost certainly be observable with modern astronomical telescopes.
Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first instance, a degenerate white dwarf may accumulate sufficient material from a binary companion, either through accretion or via a merger, to raise its core temperature enough to trigger runaway nuclear fusion, completely disrupting the star. In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical mechanics have been established and accepted by most astronomers for some time.
Supernovae can expel several solar masses of material at speeds up to several percent of the speed of light. This drives an expanding and fast-moving 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 through to rubidium. The expanding shock waves of supernova can trigger the formation of new stars. Supernova remnants might be a major source of cosmic rays. Supernovae might produce strong gravitational waves, though, thus far, the gravitational waves detected have been from the merger of black holes and neutron stars.Supernova remnant
A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.
There are two common routes to a supernova: either a massive star may run out of fuel, ceasing to generate fusion energy in its core, and collapsing inward under the force of its own gravity to form a neutron star or a black hole; or a white dwarf star may accrete material from a companion star until it reaches a critical mass and undergoes a thermonuclear explosion.
In either case, the resulting supernova explosion expels much or all of the stellar material with velocities as much as 10% the speed of light (or approximately 30,000 km/s). These ejecta are highly supersonic: assuming a typical temperature of the interstellar medium of 10,000 K, the Mach number can initially be > 1000. Therefore, a strong shock wave forms ahead of the ejecta, that heats the upstream plasma up to temperatures well above millions of K. The shock continuously slows down over time as it sweeps up the ambient medium, but it can expand over hundreds or thousands of years and over tens of parsecs before its speed falls below the local sound speed.
One of the best observed young supernova remnants was formed by SN 1987A, a supernova in the Large Magellanic Cloud that was observed in February 1987. Other well-known supernova remnants include the Crab Nebula; Tycho, the remnant of SN 1572, named after Tycho Brahe who recorded the brightness of its original explosion; and Kepler, the remnant of SN 1604, named after Johannes Kepler. The youngest known remnant in our galaxy is G1.9+0.3, discovered in the galactic center.Timeline of stellar astronomy
Timeline of stellar astronomy
2300 BC — First great period of star naming in China.
134 BC — Hipparchus creates the magnitude scale of stellar apparent luminosities
185 AD — Chinese astronomers become the first to observe a supernova, the SN 185
964 — Abd al-Rahman al-Sufi (Azophi) writes the Book of Fixed Stars, in which he makes the first recorded observations of the Andromeda Galaxy and the Large Magellanic Cloud, and lists numerous stars with their positions, magnitudes, brightness, and colour, and gives drawings for each constellation
1000s (decade) — The Persian astronomer, Abū Rayhān al-Bīrūnī, describes the Milky Way galaxy as a collection of numerous nebulous stars
1006 — Ali ibn Ridwan and Chinese astronomers observe the SN 1006, the brightest stellar event ever recorded
1054 — Chinese and Arab astronomers observe the SN 1054, responsible for the creation of the Crab Nebula, the only nebula whose creation was observed
1181 — Chinese astronomers observe the SN 1181 supernova
1580 — Taqi al-Din measures the right ascension of the stars at the Constantinople Observatory of Taqi ad-Din using an "observational clock" he invented and which he described as "a mechanical clock with three dials which show the hours, the minutes, and the seconds"
1596 — David Fabricius notices that Mira's brightness varies
1672 — Geminiano Montanari notices that Algol's brightness varies
1686 — Gottfried Kirch notices that Chi Cygni's brightness varies
1718 — Edmund Halley discovers stellar proper motions by comparing his astrometric measurements with those of the Greeks
1782 — John Goodricke notices that the brightness variations of Algol are periodic and proposes that it is partially eclipsed by a body moving around it
1784 — Edward Pigott discovers the first Cepheid variable star
1838 — Thomas Henderson, Friedrich Struve, and Friedrich Bessel measure stellar parallaxes
1844 — Friedrich Bessel explains the wobbling motions of Sirius and Procyon by suggesting that these stars have dark companions
1906 — Arthur Eddington begins his statistical study of stellar motions
1908 — Henrietta Leavitt discovers the Cepheid period-luminosity relation
1910 — Ejnar Hertzsprung and Henry Norris Russell study the relation between magnitudes and spectral types of stars
1924 — Arthur Eddington develops the main sequence mass-luminosity relationship
1929 — George Gamow proposes hydrogen fusion as the energy source for stars
1938 — Hans Bethe and Carl von Weizsäcker detail the proton-proton chain and CNO cycle in stars
1939 — Rupert Wildt realizes the importance of the negative hydrogen ion for stellar opacity
1952 — Walter Baade distinguishes between Cepheid I and Cepheid II variable stars
1953 — Fred Hoyle predicts a carbon-12 resonance to allow stellar triple alpha reactions at reasonable stellar interior temperatures
1961 — Chūshirō Hayashi publishes his work on the Hayashi track of fully convective stars
1963 — Fred Hoyle and William A. Fowler conceive the idea of supermassive stars
1964 — Subrahmanyan Chandrasekhar and Richard Feynman develop a general relativistic theory of stellar pulsations and show that supermassive stars are subject to a general relativistic instability
1967 — Eric Becklin and Gerry Neugebauer discover the Becklin-Neugebauer Object at 10 micrometres
1977 — (May 25) The Star Wars film is released and became a worldwide phenomenon, boosting interests in stellar systems.
2012 — (May 2) First visual proof of existence of black-holes. Suvi Gezari's team in Johns Hopkins University, using the Hawaiian telescope Pan-STARRS 1, publish images of a supermassive black hole 2.7 million light-years away swallowing a red giant.Timeline of white dwarfs, neutron stars, and supernovae
Timeline of neutron stars, pulsars, supernovae, and white dwarfs
Note that this list is mainly about the development of knowledge, but also about some supernovae taking place. For a separate list of the latter, see the article List of supernovae. All dates refer to when the supernova was observed on Earth or would have been observed on Earth had powerful enough telescopes existed at the time.Type Ia supernova
A type Ia supernova (read "type one-a") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.Physically, carbon–oxygen white dwarfs with a low rate of rotation are limited to below 1.44 solar masses (M☉). Beyond this, they reignite and in some cases trigger a supernova explosion. Somewhat confusingly, this limit is often referred to as the Chandrasekhar mass, despite being marginally different from the absolute Chandrasekhar limit where electron degeneracy pressure is unable to prevent catastrophic collapse. If a white dwarf gradually accretes mass from a binary companion, the general hypothesis is that its core will reach the ignition temperature for carbon fusion as it approaches the limit.
However, if the white dwarf merges with another white dwarf (a very rare event), it will momentarily exceed the limit and begin to collapse, again raising its temperature past the nuclear fusion ignition point. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction, releasing enough energy (1–2×1044 J) to unbind the star in a supernova explosion.This type Ia category of supernovae produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. The stability of this value allows these explosions to be used as standard candles to measure the distance to their host galaxies because the visual magnitude of the supernovae depends primarily on the distance.
In May 2015, NASA reported that the Kepler space observatory observed KSN 2011b, a type Ia supernova in the process of exploding. Details of the pre-nova moments may help scientists better judge the quality of Type Ia supernovae as standard candles, which is an important link in the argument for dark energy.White dwarf
A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. A white dwarf's faint luminosity comes from the emission of stored thermal energy; no fusion takes place in a white dwarf. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name white dwarf was coined by Willem Luyten in 1922.
White dwarfs are thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star, that of about 10 solar masses. This includes over 97% of the other stars in the Milky Way., § 1. After the hydrogen-fusing period of a main-sequence star of low or medium mass ends, such a star will expand to a red giant during which it fuses helium to carbon and oxygen in its core by the triple-alpha process. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon (around 1 billion K), an inert mass of carbon and oxygen will build up at its center. After such a star sheds its outer layers and forms a planetary nebula, it will leave behind a core, which is the remnant white dwarf. Usually, white dwarfs are composed of carbon and oxygen. If the mass of the progenitor is between 8 and 10.5 solar masses (M☉), the core temperature will be sufficient to fuse carbon but not neon, in which case an oxygen–neon–magnesium white dwarf may form. Stars of very low mass will not be able to fuse helium, hence, a helium white dwarf may form by mass loss in binary systems.
The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy. As a result, it cannot support itself by the heat generated by fusion against gravitational collapse, but is supported only by electron degeneracy pressure, causing it to be extremely dense. The physics of degeneracy yields a maximum mass for a non-rotating white dwarf, the Chandrasekhar limit—approximately 1.44 times of M☉—beyond which it cannot be supported by electron degeneracy pressure. A carbon-oxygen white dwarf that approaches this mass limit, typically by mass transfer from a companion star, may explode as a type Ia supernova via a process known as carbon detonation; SN 1006 is thought to be a famous example.
A white dwarf is very hot when it forms, but because it has no source of energy, it will gradually cool as it radiates its energy. This means that its radiation, which initially has a high color temperature, will lessen and redden with time. Over a very long time, a white dwarf will cool and its material will begin to crystallize, starting with the core. The star's low temperature means it will no longer emit significant heat or light, and it will become a cold black dwarf. Because the length of time it takes for a white dwarf to reach this state is calculated to be longer than the current age of the universe (approximately 13.8 billion years), it is thought that no black dwarfs yet exist. The oldest white dwarfs still radiate at temperatures of a few thousand kelvins.