Шаңбұлт Қызыл Ине (Shańbult Qyzyl İne)

Supernova remnant in the constellation Taurus

At an apparent magnitude of 8.4, comparable to that of Saturn's moon Titan, it is not visible to the naked eye but can be made out using binoculars under favourable conditions. The nebula lies in the Perseus Arm of the Milky Way galaxy, at a distance of about from Earth. It has a diameter of , corresponding to an apparent diameter of some 7 arcminutes, and is expanding at a rate of about , or 0.5% of the speed of light. At the center of the nebula lies the Crab Pulsar, a neutron star across with a spin rate of 30.2 times per second, which emits pulses of radiation from gamma rays to radio waves. At X ray and gamma ray energies above 30 keV, the Crab Nebula is generally the brightest persistent gamma ray source in the sky, with measured flux extending to above 10 TeV. The nebula's radiation allows detailed study of celestial bodies that occult it. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab Nebula's radio waves passing through it, and in 2003, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X rays from the nebula.

The earliest recorded documentation of observation of astronomical object SN 1054 was as it was occurring in 1054, by Chinese astrononomers and Japanese observers, hence its numerical identification. Modern understanding that the Crab Nebula was created by a supernova traces back to 1921, when Carl Otto Lampland announced he had seen changes in the nebula's structure.

The Crab Nebula was first identified in 1731 by John Bevis. The nebula was independently rediscovered in 1758 by Charles Messier as he was observing a bright comet. After some observation, noticing that the object that he was observing was not moving across the sky, Messier concluded that the object was not a comet. Messier then realised the usefulness of compiling a catalogue of celestial objects of a cloudy nature, but fixed in the sky, to avoid incorrectly cataloguing them as comets. This realization led him to compile the "Messier catalogue".

The Crab Nebula was the first astronomical object recognized as being connected to a supernova explosion. In 1913, when Vesto Slipher registered his spectroscopy study of the sky, the Crab Nebula was again one of the first objects to be studied. Changes in the cloud, suggesting its small extent, were discovered by Carl Lampland in 1921. That same year, John Charles Duncan demonstrated that the remnant was expanding, while Knut Lundmark noted its proximity to the guest star of 1054. In 1928, Edwin Hubble proposed associating the cloud with the star of 1054, an idea that remained controversial until the nature of supernovae was understood, and it was Nicholas Mayall who indicated that the star of 1054 was undoubtedly the supernova whose explosion produced the Crab Nebula. The search for historical supernovae started at that moment: seven other historical sightings have been found by comparing modern observations of supernova remnants with astronomical documents of past centuries. After the original connection to Chinese observations, in 1934 connections were made to a 13th century Japanese reference to a "guest star" in Meigetsuki a few weeks before the Chinese reference. The event was long considered unrecorded in Islamic astronomy, but in 1978 a reference was found in a 13th century copy made by Ibn Abi Usaibia of a work by Ibn Butlan, a Nestorian Christian physician active in Baghdad at the time of the supernova. Given its great distance, the daytime "guest star" observed by the Chinese could only have been a supernova—a massive, exploding star, having exhausted its supply of energy from nuclear fusion and collapsed in on itself. Recent analysis of historical records have found that the supernova that created the Crab Nebula probably appeared in April or early May, rising to its maximum brightness of between apparent magnitude −7 and −4.5 (brighter even than Venus' −4.2 and everything in the night sky except the Moon) by July. The supernova was visible to the naked eye for about two years after its first observation.

In the 1960s, because of the prediction and discovery of pulsars, the Crab Nebula again became a major center of interest. It was then that Franco Pacini predicted the existence of the Crab Pulsar for the first time, which would explain the brightness of the cloud. In late 1968, David H. Staelin and Edward C. Reifenstein III reported the discovery of two rapidly variable radio sources in the area of the Crab Nebula using the Green Bank Telescope. They named them NP 0527 and NP 0532. The period of 33 milliseconds and precise location of the Crab Nebula pulsar NP 0532 was discovered by Richard V. E. Lovelace and collaborators on 10 November 1968 at the Arecibo Observatory. This discovery also proved that pulsars are rotating neutron stars (not pulsating white dwarfs, as many scientists suggested). Soon after the discovery of the Crab Pulsar, David Richards discovered (using the Arecibo Observatory) that the Crab Pulsar spins down and, therefore, the pulsar loses its rotational energy. Thomas Gold has shown that the spin down power of the pulsar is sufficient to power the Crab Nebula. The discovery of the Crab Pulsar and the knowledge of its exact age (almost to the day) allows for the verification of basic physical properties of these objects, such as characteristic age and spin down luminosity, the orders of magnitude involved (notably the strength of the magnetic field), along with various aspects related to the dynamics of the remnant. The role of this supernova to the scientific understanding of supernova remnants was crucial, as no other historical supernova created a pulsar whose precise age is known for certain. The only possible exception to this rule would be SN 1181, whose supposed remnant 3C 58 is home to a pulsar, but its identification using Chinese observations from 1181 is contested. The inner part of the Crab Nebula is dominated by a pulsar wind nebula enveloping the pulsar. Some sources consider the Crab Nebula to be an example of both a pulsar wind nebula as well as a supernova remnant, while others separate the two phenomena based on the different sources of energy production and behaviour. which opened the VHE gamma ray window and led to the detection of numerous VHE sources since then. In 2019 the Crab Nebula was observed to emit gamma rays in excess of 100 TeV, making it the first identified source beyond 100 TeV.

In visible light, the Crab Nebula consists of a broadly oval shaped mass of filaments, about 6 arcminutes long and 4 arcminutes wide (by comparison, the full moon is 30 arcminutes across) surrounding a diffuse blue central region. In three dimensions, the nebula is thought to be shaped either like an oblate spheroid (estimated as away) or a prolate spheroid (estimated as away). In 1953, Iosif Shklovsky proposed that the diffuse blue region is predominantly produced by synchrotron radiation, which is radiation given off by the curving motion of electrons in a magnetic field. The radiation corresponded to electrons moving at speeds up to half the speed of light. Three years later, the hypothesis was confirmed by observations. In the 1960s it was found that the source of the curved paths of the electrons was the strong magnetic field produced by a neutron star at the centre of the nebula.

Even though the Crab Nebula is the focus of much attention among astronomers, its distance remains an open question, owing to uncertainties in every method used to estimate its distance. In 2008, the consensus was that its distance from Earth is Images taken several years apart reveal the slow expansion of the nebula, and by comparing this angular expansion with its spectroscopically determined expansion velocity, the nebula's distance can be estimated. In 1973, an analysis of many methods used to compute the distance to the nebula had reached a conclusion of about , consistent with the currently cited value. Tracing back its expansion (assuming a constant decrease of expansion speed due to the nebula's mass) yielded a date for the creation of the nebula several decades after 1054, implying that its outward velocity has decelerated less than assumed since the supernova explosion. This reduced deceleration is believed to be caused by energy from the pulsar that feeds into the nebula's magnetic field, which expands and forces the nebula's filaments outward.

Estimates of the total mass of the nebula are important for estimating the mass of the supernova's progenitor star. The amount of matter contained in the Crab Nebula's filaments (ejecta mass of ionized and neutral gas; mostly helium) is estimated to be 4.6.

One of the many nebular components (or anomalies) of the Crab Nebula is a helium rich torus which is visible as an east–west band crossing the pulsar region. The torus composes about 25% of the visible ejecta. However, it is suggested by calculation that about 95% of the torus is helium. As yet, there has been no plausible explanation put forth for the structure of the torus. The region around the star was found to be a strong source of radio waves in 1949 and X rays in 1963, and was identified as one of the brightest objects in the sky in gamma rays in 1967. Then, in 1968, the star was found to be emitting its radiation in rapid pulses, becoming one of the first pulsars to be discovered. However, the discovery of a pulsating radio source in the centre of the Crab Nebula was strong evidence that pulsars were formed by supernova explosions. They now are understood to be rapidly rotating neutron stars, whose powerful magnetic fields concentrates their radiation emissions into narrow beams. The Crab Pulsar is believed to be about in diameter; it emits pulses of radiation every 33 milliseconds. Pulses are emitted at wavelengths across the electromagnetic spectrum, from radio waves to X rays. Like all isolated pulsars, its period is slowing very gradually. Occasionally, its rotational period shows sharp changes, known as 'glitches', which are believed to be caused by a sudden realignment inside the neutron star. The energy released as the pulsar slows down is enormous, and it powers the emission of the synchrotron radiation of the Crab Nebula, which has a total luminosity about 75,000 times greater than that of the Sun. The pulsar's extreme energy output creates an unusually dynamic region at the centre of the Crab Nebula. While most astronomical objects evolve so slowly that changes are visible only over timescales of many years, the inner parts of the Crab Nebula show changes over timescales of only a few days. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the bulk of the nebula, forming a shock front. The shape and position of this feature shifts rapidly, with the equatorial wind appearing as a series of wisp like features that steepen, brighten, then fade as they move away from the pulsar to well out into the main body of the nebula. so the pulsar in the Crab Nebula shows it must have formed in a core collapse supernova. Theoretical models of supernova explosions suggest that the star that exploded to produce the Crab Nebula must have had a mass of between Stars with masses lower than are thought to be too small to produce supernova explosions, and end their lives by producing a planetary nebula instead, while a star heavier than would have produced a nebula with a different chemical composition from that observed in the Crab Nebula. Recent studies, however, suggest the progenitor could have been a super asymptotic giant branch star in the range that would have exploded in an electron capture supernova. In June 2021 a paper in the journal Nature Astronomy reported that the 2018 supernova SN 2018zd (in the galaxy NGC 2146, about 31 million light years from Earth) appeared to be the first observation of an electron capture supernova The 1054 supernova explosion that created the Crab Nebula had been thought to be the best candidate for an electron capture supernova, and the 2021 paper makes it more likely that this was correct.

The Crab Nebula lies roughly 1.5 degrees away from the ecliptic—the plane of Earth's orbit around the Sun. This means that the Moon—and occasionally, planets—can transit or occult the nebula. Although the Sun does not transit the nebula, its corona passes in front of it. These transits and occultations can be used to analyse both the nebula and the object passing in front of it, by observing how radiation from the nebula is altered by the transiting body.

Lunar transits have been used to map X ray emissions from the nebula. Before the launch of X ray observing satellites, such as the Chandra X ray Observatory, X ray observations generally had quite low angular resolution, but when the Moon passes in front of the nebula, its position is very accurately known, and so the variations in the nebula's brightness can be used to create maps of X ray emission. When X rays were first observed from the Crab Nebula, a lunar occultation was used to determine the exact location of their source.

Very rarely, Saturn transits the Crab Nebula. Its transit on 4 January 2003 (UTC) was the first since 31 December 1295 (O. S.); another will not occur until 5 August 2267. Researchers used the Chandra X ray Observatory to observe Saturn's moon Titan as it crossed the nebula, and found that Titan's X ray 'shadow' was larger than its solid surface, due to absorption of X rays in its atmosphere. These observations showed that the thickness of Titan's atmosphere is The transit of Saturn itself could not be observed, because Chandra was passing through the Van Allen belts at the time.