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108-403: The name also emphasizes two main features of the installation, namely the simultaneous observation of air showers with several telescopes, under different viewing angles, and the combination of telescopes to a large system to increase the effective detection area for gamma rays. H.E.S.S. permits the exploration of gamma-ray sources with intensities at a level of a few thousandth parts of the flux of

216-455: A French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium . Villard knew that his described radiation was more powerful than previously described types of rays from radium, which included beta rays, first noted as "radioactivity" by Henri Becquerel in 1896, and alpha rays, discovered as a less penetrating form of radiation by Rutherford, in 1899. However, Villard did not consider naming them as

324-506: 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 ". William Herschel observed the Crab Nebula numerous times between 1783 and 1809, but it is not known whether he was aware of its existence in 1783, or if he discovered it independently of Messier and Bevis. After several observations, he concluded that it

432-438: A crystal. The immobilization of nuclei at both ends of a gamma resonance interaction is required so that no gamma energy is lost to the kinetic energy of recoiling nuclei at either the emitting or absorbing end of a gamma transition. Such loss of energy causes gamma ray resonance absorption to fail. However, when emitted gamma rays carry essentially all of the energy of the atomic nuclear de-excitation that produces them, this energy

540-415: A different fundamental type. Later, in 1903, Villard's radiation was recognized as being of a type fundamentally different from previously named rays by Ernest Rutherford , who named Villard's rays "gamma rays" by analogy with the beta and alpha rays that Rutherford had differentiated in 1899. The "rays" emitted by radioactive elements were named in order of their power to penetrate various materials, using

648-478: A few weeks, suggesting their relatively small size (less than a few light-weeks across). Such sources of gamma and X-rays are the most commonly visible high intensity sources outside the Milky Way galaxy. They shine not in bursts (see illustration), but relatively continuously when viewed with gamma ray telescopes. The power of a typical quasar is about 10 watts, a small fraction of which is gamma radiation. Much of

756-448: A formidable radiation protection challenge, requiring shielding made from dense materials such as lead or concrete. On Earth , the magnetosphere protects life from most types of lethal cosmic radiation other than gamma rays. The first gamma ray source to be discovered was the radioactive decay process called gamma decay . In this type of decay, an excited nucleus emits a gamma ray almost immediately upon formation. Paul Villard ,

864-455: A magnetic field indicated that they had no charge. In 1914, gamma rays were observed to be reflected from crystal surfaces, proving that they were electromagnetic radiation. Rutherford and his co-worker Edward Andrade measured the wavelengths of gamma rays from radium, and found they were similar to X-rays , but with shorter wavelengths and thus, higher frequency. This was eventually recognized as giving them more energy per photon , as soon as

972-457: A means for sources of GeV photons using lasers as exciters through a controlled interplay between the cascade and anomalous radiative trapping . Thunderstorms can produce a brief pulse of gamma radiation called a terrestrial gamma-ray flash . These gamma rays are thought to be produced by high intensity static electric fields accelerating electrons, which then produce gamma rays by bremsstrahlung as they collide with and are slowed by atoms in

1080-408: A nuclear power plant, shielding can be provided by steel and concrete in the pressure and particle containment vessel, while water provides a radiation shielding of fuel rods during storage or transport into the reactor core. The loss of water or removal of a "hot" fuel assembly into the air would result in much higher radiation levels than when kept under water. When a gamma ray passes through matter,

1188-554: A number of astronomical processes in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms of bremsstrahlung , inverse Compton scattering and synchrotron radiation . A large fraction of such astronomical gamma rays are screened by Earth's atmosphere. Notable artificial sources of gamma rays include fission , such as occurs in nuclear reactors , as well as high energy physics experiments, such as neutral pion decay and nuclear fusion . A sample of gamma ray-emitting material that

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1296-558: A shell, none has yet been found. 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

1404-434: A source of petaelectronvolt galactic cosmic rays. Crab Nebula The Crab Nebula (catalogue designations M1 , NGC 1952 , Taurus A ) is a supernova remnant and pulsar wind nebula in the constellation of Taurus . The common name comes from a drawing that somewhat resembled a crab with arms produced by William Parsons, 3rd Earl of Rosse , in 1842 or 1843 using a 36-inch (91 cm) telescope . The nebula

1512-423: A spin rate of 30.2 times per second, lies at the center of the Crab Nebula. The star 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

1620-532: A supernova is referred to as the supernova's progenitor star . Two types of stars explode as supernovae: white dwarfs and massive stars . In the so-called Type Ia supernovae , gases falling onto a 'dead' white dwarf raise its mass until it nears a critical level, the Chandrasekhar limit , resulting in a runaway nuclear fusion explosion that obliterates the star; in Type Ib/c and Type II supernovae,

1728-403: Is also a mode of relaxation of many excited states of atomic nuclei following other types of radioactive decay, such as beta decay, so long as these states possess the necessary component of nuclear spin . When high-energy gamma rays, electrons, or protons bombard materials, the excited atoms emit characteristic "secondary" gamma rays, which are products of the creation of excited nuclear states in

1836-620: Is also sufficient to excite the same energy state in a second immobilized nucleus of the same type. Gamma rays provide information about some of the most energetic phenomena in the universe; however, they are largely absorbed by the Earth's atmosphere. Instruments aboard high-altitude balloons and satellites missions, such as the Fermi Gamma-ray Space Telescope , provide our only view of the universe in gamma rays. Gamma-induced molecular changes can also be used to alter

1944-448: Is another possible mechanism of gamma ray production. Neutron stars with a very high magnetic field ( magnetars ), thought to produce astronomical soft gamma repeaters , are another relatively long-lived star-powered source of gamma radiation. More powerful gamma rays from very distant quasars and closer active galaxies are thought to have a gamma ray production source similar to a particle accelerator . High energy electrons produced by

2052-403: Is classified as X-rays and is the subject of X-ray astronomy . Gamma rays are ionizing radiation and are thus hazardous to life. They can cause DNA mutations , cancer and tumors , and at high doses burns and radiation sickness . Due to their high penetration power, they can damage bone marrow and internal organs. Unlike alpha and beta rays, they easily pass through the body and thus pose

2160-446: Is close to the edge of the visible universe . Due to their penetrating nature, gamma rays require large amounts of shielding mass to reduce them to levels which are not harmful to living cells, in contrast to alpha particles , which can be stopped by paper or skin, and beta particles , which can be shielded by thin aluminium. Gamma rays are best absorbed by materials with high atomic numbers ( Z ) and high density, which contribute to

2268-427: Is defined as the probability of cancer induction and genetic damage. The International Commission on Radiological Protection says "In the low dose range, below about 100 mSv, it is scientifically plausible to assume that the incidence of cancer or heritable effects will rise in direct proportion to an increase in the equivalent dose in the relevant organs and tissues" High doses produce deterministic effects, which

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2376-404: Is dominated by the more common and longer-term production of gamma rays that emanate from pulsars within the Milky Way. Sources from the rest of the sky are mostly quasars . Pulsars are thought to be neutron stars with magnetic fields that produce focused beams of radiation, and are far less energetic, more common, and much nearer sources (typically seen only in our own galaxy) than are quasars or

2484-502: Is estimated to be between 1.4 and 2  M ☉ . The predominant theory to account for the missing mass of the Crab Nebula is that a substantial proportion of the mass of the progenitor was carried away before the supernova explosion in a fast stellar wind , a phenomenon commonly seen in Wolf–Rayet stars . However, this would have created a shell around the nebula. Although attempts have been made at several wavelengths to observe

2592-438: Is expanding outward at about 1,500 km/s (930 mi/s). 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 1.9 kpc (6,300 ly), consistent with

2700-419: Is followed 99.88% of the time: Another example is the alpha decay of Am to form Np ; which is followed by gamma emission. In some cases, the gamma emission spectrum of the daughter nucleus is quite simple, (e.g. Co / Ni ) while in other cases, such as with ( Am / Np and Ir / Pt ),

2808-414: Is much slower in the case of a low-dose exposure. Studies have shown low-dose gamma radiation may be enough to cause cancer. In a study of mice, they were given human-relevant low-dose gamma radiation, with genotoxic effects 45 days after continuous low-dose gamma radiation, with significant increases of chromosomal damage, DNA lesions and phenotypic mutations in blood cells of irradiated animals, covering

2916-408: Is the severity of acute tissue damage that is certain to happen. These effects are compared to the physical quantity absorbed dose measured by the unit gray (Gy). When gamma radiation breaks DNA molecules, a cell may be able to repair the damaged genetic material, within limits. However, a study of Rothkamm and Lobrich has shown that this repair process works well after high-dose exposure but

3024-499: Is used for irradiating or imaging is known as a gamma source. It is also called a radioactive source , isotope source, or radiation source, though these more general terms also apply to alpha and beta-emitting devices. Gamma sources are usually sealed to prevent radioactive contamination , and transported in heavy shielding. Gamma rays are produced during gamma decay, which normally occurs after other forms of decay occur, such as alpha or beta decay. A radioactive nucleus can decay by

3132-674: The Arecibo Radio 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

3240-517: The Crab Nebula . H.E.S.S. consists of five telescopes: four with mirrors just under 12 m in diameter, arranged as a square with 120 m sides, and one larger telescope with a 28 m mirror, located at the centre of the array. The four 12 m telescopes began operation in 2004, with the 28 m telescope added as an upgrade (called H.E.S.S. II) in 2012. As with other gamma-ray telescopes, H.E.S.S. observes high energy processes in

3348-673: The Cygnus X-3 microquasar . Natural sources of gamma rays originating on Earth are mostly a result of radioactive decay and secondary radiation from atmospheric interactions with cosmic ray particles. However, there are other rare natural sources, such as terrestrial gamma-ray flashes , which produce gamma rays from electron action upon the nucleus. Notable artificial sources of gamma rays include fission , such as that which occurs in nuclear reactors , and high energy physics experiments, such as neutral pion decay and nuclear fusion . The energy ranges of gamma rays and X-rays overlap in

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3456-541: The Perseus Arm of the Milky Way galaxy, at a distance of about 2.0 kiloparsecs (6,500  ly ) from Earth. It has a diameter of 3.4 parsecs (11 ly), corresponding to an apparent diameter of some 7  arcminutes , and is expanding at a rate of about 1,500 kilometres per second (930 mi/s), or 0.5% of the speed of light . The Crab Pulsar , a neutron star 28–30 kilometres (17–19 mi) across with

3564-402: 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

3672-455: The electromagnetic spectrum , so the terminology for these electromagnetic waves varies between scientific disciplines. In some fields of physics, they are distinguished by their origin: gamma rays are created by nuclear decay while X-rays originate outside the nucleus. In astrophysics , gamma rays are conventionally defined as having photon energies above 100 keV and are the subject of gamma-ray astronomy , while radiation below 100 keV

3780-459: The extragalactic background light in the universe: The highest-energy rays interact more readily with the background light photons and thus the density of the background light may be estimated by analyzing the incoming gamma ray spectra. Gamma spectroscopy is the study of the energetic transitions in atomic nuclei, which are generally associated with the absorption or emission of gamma rays. As in optical spectroscopy (see Franck–Condon effect)

3888-679: 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 1,380 pc/4,500 ly away) or a prolate spheroid (estimated as 2,020 pc/6,600 ly away). The filaments are the remnants of the progenitor star's atmosphere, and consist largely of ionised helium and hydrogen , along with carbon , oxygen , nitrogen , iron , neon and sulfur . The filaments' temperatures are typically between 11,000 and 18,000  K , and their densities are about 1,300 particles per cm . In 1953, Iosif Shklovsky proposed that

3996-472: 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

4104-400: 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. At the center of the Crab Nebula are two faint stars, one of which is

4212-463: 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. The Crab Nebula was the first astrophysical object confirmed to emit gamma rays in the very-high-energy (VHE) band above 100 GeV in energy. The VHE detection

4320-506: 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. This eventually led to the conclusion that the creation of the Crab Nebula corresponds to the bright SN 1054 supernova recorded by medieval astronomers in AD 1054. The Crab Nebula was first identified in 1731 by John Bevis . The nebula was independently rediscovered in 1758 by Charles Messier as he

4428-457: The Crab Nebula, a lunar occultation was used to determine the exact location of their source. The Sun's corona passes in front of the Crab Nebula every June. Variations in the radio waves received from the Crab Nebula at this time can be used to infer details about the corona's density and structure. Early observations established that the corona extended out to much greater distances than had previously been thought; later observations found that

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4536-427: 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

4644-411: The Crab Nebula. Recent studies, however, suggest the progenitor could have been a super-asymptotic giant branch star in the 8 to 10  M ☉ 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

4752-597: The Gamsberg mountain, an area well known for its excellent optical quality. The first of the four telescopes of Phase I of the H.E.S.S. project went into operation in Summer 2002; all four were operational in December 2003. In 2004 H.E.S.S. was the first IACT experiment to spatially resolve a source of cosmic gamma rays . In 2005, it was announced that H.E.S.S. had detected eight new high-energy gamma ray sources, doubling

4860-420: The K shell electrons of the atom, causing it to be ejected from that atom, in a process generally termed the photoelectric effect (external gamma rays and ultraviolet rays may also cause this effect). The photoelectric effect should not be confused with the internal conversion process, in which a gamma ray photon is not produced as an intermediate particle (rather, a "virtual gamma ray" may be thought to mediate

4968-500: The absorption of gamma rays by a nucleus is especially likely (i.e., peaks in a "resonance") when the energy of the gamma ray is the same as that of an energy transition in the nucleus. In the case of gamma rays, such a resonance is seen in the technique of Mössbauer spectroscopy . In the Mössbauer effect the narrow resonance absorption for nuclear gamma absorption can be successfully attained by physically immobilizing atomic nuclei in

5076-715: The annihilating electron and positron are at rest, each of the resulting gamma rays has an energy of ~ 511 keV and frequency of ~ 1.24 × 10  Hz . Similarly, a neutral pion most often decays into two photons. Many other hadrons and massive bosons also decay electromagnetically. High energy physics experiments, such as the Large Hadron Collider , accordingly employ substantial radiation shielding. Because subatomic particles mostly have far shorter wavelengths than atomic nuclei, particle physics gamma rays are generally several orders of magnitude more energetic than nuclear decay gamma rays. Since gamma rays are at

5184-441: The atmosphere. Gamma rays up to 100 MeV can be emitted by terrestrial thunderstorms, and were discovered by space-borne observatories. This raises the possibility of health risks to passengers and crew on aircraft flying in or near thunderclouds. The most effusive solar flares emit across the entire EM spectrum, including γ-rays. The first confident observation occurred in 1972 . Extraterrestrial, high energy gamma rays include

5292-470: The average 10 seconds. Such relatively long-lived excited nuclei are termed nuclear isomers , and their decays are termed isomeric transitions . Such nuclei have half-lifes that are more easily measurable, and rare nuclear isomers are able to stay in their excited state for minutes, hours, days, or occasionally far longer, before emitting a gamma ray. The process of isomeric transition is therefore similar to any gamma emission, but differs in that it involves

5400-482: The bombarded atoms. Such transitions, a form of nuclear gamma fluorescence , form a topic in nuclear physics called gamma spectroscopy . Formation of fluorescent gamma rays are a rapid subtype of radioactive gamma decay. In certain cases, the excited nuclear state that follows the emission of a beta particle or other type of excitation, may be more stable than average, and is termed a metastable excited state, if its decay takes (at least) 100 to 1000 times longer than

5508-496: The cancer often has a higher metabolic rate than the surrounding tissues. The most common gamma emitter used in medical applications is the nuclear isomer technetium-99m which emits gamma rays in the same energy range as diagnostic X-rays. When this radionuclide tracer is administered to a patient, a gamma camera can be used to form an image of the radioisotope's distribution by detecting the gamma radiation emitted (see also SPECT ). Depending on which molecule has been labeled with

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5616-496: The cancerous cells. The beams are aimed from different angles to concentrate the radiation on the growth while minimizing damage to surrounding tissues. Gamma rays are also used for diagnostic purposes in nuclear medicine in imaging techniques. A number of different gamma-emitting radioisotopes are used. For example, in a PET scan a radiolabeled sugar called fluorodeoxyglucose emits positrons that are annihilated by electrons, producing pairs of gamma rays that highlight cancer as

5724-445: 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 28–30 km (17–19 mi) in diameter; it emits pulses of radiation every 33  milliseconds . Pulses are emitted at wavelengths across

5832-528: 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

5940-663: The collision of pairs of neutron stars, or a neutron star and a black hole . The so-called long-duration gamma-ray bursts produce a total energy output of about 10 joules (as much energy as the Sun will produce in its entire life-time) but in a period of only 20 to 40 seconds. Gamma rays are approximately 50% of the total energy output. The leading hypotheses for the mechanism of production of these highest-known intensity beams of radiation, are inverse Compton scattering and synchrotron radiation from high-energy charged particles. These processes occur as relativistic charged particles leave

6048-399: The comet should appear in the constellation of Taurus . It was in searching in vain for the comet that Charles Messier found the Crab Nebula, which he at first thought to be Halley's 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

6156-568: The corona contained substantial density variations. 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

6264-399: 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

6372-438: The daytime had been recorded in the same part of the sky by Chinese astronomers on 4 July 1054, and probably also by Japanese observers. 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

6480-399: 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

6588-479: The emission of an α or β particle. The daughter nucleus that results is usually left in an excited state. It can then decay to a lower energy state by emitting a gamma ray photon, in a process called gamma decay. The emission of a gamma ray from an excited nucleus typically requires only 10 seconds. Gamma decay may also follow nuclear reactions such as neutron capture , nuclear fission , or nuclear fusion. Gamma decay

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6696-562: The energy of the gamma rays, the thicker the shielding made from the same shielding material is required. Materials for shielding gamma rays are typically measured by the thickness required to reduce the intensity of the gamma rays by one half (the half-value layer or HVL). For example, gamma rays that require 1 cm (0.4 inch) of lead to reduce their intensity by 50% will also have their intensity reduced in half by 4.1 cm of granite rock, 6 cm (2.5 inches) of concrete , or 9 cm (3.5 inches) of packed soil . However,

6804-425: The energy range from a few kilo electronvolts (keV) to approximately 8 megaelectronvolts (MeV), corresponding to the typical energy levels in nuclei with reasonably long lifetimes. The energy spectrum of gamma rays can be used to identify the decaying radionuclides using gamma spectroscopy . Very-high-energy gamma rays in the 100–1000 teraelectronvolt (TeV) range have been observed from astronomical sources such as

6912-400: The first pulsars to be discovered. Pulsars are sources of powerful electromagnetic radiation , emitted in short and extremely regular pulses many times a second. They were a great mystery when discovered in 1967, and the team who identified the first one considered the possibility that it could be a signal from an advanced civilization. However, the discovery of a pulsating radio source in

7020-399: 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. A significant problem in studies of the Crab Nebula is that the combined mass of the nebula and the pulsar add up to considerably less than

7128-583: The first three letters of the Greek alphabet: alpha rays as the least penetrating, followed by beta rays, followed by gamma rays as the most penetrating. Rutherford also noted that gamma rays were not deflected (or at least, not easily deflected) by a magnetic field, another property making them unlike alpha and beta rays. Gamma rays were first thought to be particles with mass, like alpha and beta rays. Rutherford initially believed that they might be extremely fast beta particles, but their failure to be deflected by

7236-423: The gamma emission spectrum is complex, revealing that a series of nuclear energy levels exist. Gamma rays are produced in many processes of particle physics . Typically, gamma rays are the products of neutral systems which decay through electromagnetic interactions (rather than a weak or strong interaction). For example, in an electron–positron annihilation , the usual products are two gamma ray photons. If

7344-513: The gamma ray background produced when cosmic rays (either high speed electrons or protons) collide with ordinary matter, producing pair-production gamma rays at 511 keV. Alternatively, bremsstrahlung are produced at energies of tens of MeV or more when cosmic ray electrons interact with nuclei of sufficiently high atomic number (see gamma ray image of the Moon near the end of this article, for illustration). The gamma ray sky (see illustration at right)

7452-403: 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. The star that exploded as

7560-494: The intermediate metastable excited state(s) of the nuclei. Metastable states are often characterized by high nuclear spin , requiring a change in spin of several units or more with gamma decay, instead of a single unit transition that occurs in only 10 seconds. The rate of gamma decay is also slowed when the energy of excitation of the nucleus is small. An emitted gamma ray from any type of excited state may transfer its energy directly to any electrons , but most probably to one of

7668-460: The known number of such sources. As of 2014, more than 90 sources of teraelectronvolt gamma rays were discovered by H.E.S.S. In 2016, the HESS collaboration reported deep gamma ray observations which show the presence of petaelectronvolt-protons originating from the supermassive black hole at the centre of the Milky Way, and therefore should be considered as a viable alternative to supernova remnants as

7776-551: The latter term became generally accepted. A gamma decay was then understood to usually emit a gamma photon. Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes such as potassium-40 , and also as a secondary radiation from various atmospheric interactions with cosmic ray particles. Natural terrestrial sources that produce gamma rays include lightning strikes and terrestrial gamma-ray flashes , which produce high energy emissions from natural high-energy voltages. Gamma rays are produced by

7884-402: The mass of this much concrete or soil is only 20–30% greater than that of lead with the same absorption capability. Depleted uranium is sometimes used for shielding in portable gamma ray sources , due to the smaller half-value layer when compared to lead (around 0.6 times the thickness for common gamma ray sources, i.e. Iridium-192 and Cobalt-60) and cheaper cost compared to tungsten . In

7992-623: The material (atomic density) and σ the absorption cross section in cm . As it passes through matter, gamma radiation ionizes via three processes: The secondary electrons (and/or positrons) produced in any of these three processes frequently have enough energy to produce much ionization themselves. Additionally, gamma rays, particularly high energy ones, can interact with atomic nuclei resulting in ejection of particles in photodisintegration , or in some cases, even nuclear fission ( photofission ). High-energy (from 80 GeV to ~10 TeV ) gamma rays arriving from far-distant quasars are used to estimate

8100-571: 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

8208-437: 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 ± 1.8  M ☉ . One of the many nebular components (or anomalies) of

8316-449: 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

8424-648: 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

8532-444: The predicted mass of the progenitor star, and the question of where the 'missing mass' is, remains unresolved. Estimates of the mass of the nebula are made by measuring the total amount of light emitted, and calculating the mass required, given the measured temperature and density of the nebula. Estimates range from about 1–5  M ☉ , with 2–3  M ☉ being the generally accepted value. The neutron star mass

8640-424: The probability for absorption is proportional to the thickness of the layer, the density of the material, and the absorption cross section of the material. The total absorption shows an exponential decrease of intensity with distance from the incident surface: where x is the thickness of the material from the incident surface, μ= n σ is the absorption coefficient, measured in cm , n the number of atoms per cm of

8748-471: The process). One example of gamma ray production due to radionuclide decay is the decay scheme for cobalt-60, as illustrated in the accompanying diagram. First, Co decays to excited Ni by beta decay emission of an electron of 0.31  MeV . Then the excited Ni decays to the ground state (see nuclear shell model ) by emitting gamma rays in succession of 1.17 MeV followed by 1.33 MeV . This path

8856-419: The progenitor star is a massive star whose core runs out of fuel to power its nuclear fusion reactions and collapses in on itself, releasing gravitational potential energy in a form that blows away the star's outer layers. Type Ia supernovae do not produce pulsars, so the pulsar in the Crab Nebula shows it must have formed in a core-collapse supernova. Theoretical models of supernova explosions suggest that

8964-466: The properties of semi-precious stones , and is often used to change white topaz into blue topaz . Non-contact industrial sensors commonly use sources of gamma radiation in refining, mining, chemicals, food, soaps and detergents, and pulp and paper industries, for the measurement of levels, density, and thicknesses. Gamma-ray sensors are also used for measuring the fluid levels in water and oil industries. Typically, these use Co-60 or Cs-137 isotopes as

9072-403: 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

9180-553: The quasar, and subjected to inverse Compton scattering, synchrotron radiation , or bremsstrahlung, are the likely source of the gamma rays from those objects. It is thought that a supermassive black hole at the center of such galaxies provides the power source that intermittently destroys stars and focuses the resulting charged particles into beams that emerge from their rotational poles. When those beams interact with gas, dust, and lower energy photons they produce X-rays and gamma rays. These sources are known to fluctuate with durations of

9288-553: The radiation source. In the US, gamma ray detectors are beginning to be used as part of the Container Security Initiative (CSI). These machines are advertised to be able to scan 30 containers per hour. Gamma radiation is often used to kill living organisms, in a process called irradiation . Applications of this include the sterilization of medical equipment (as an alternative to autoclaves or chemical means),

9396-638: The rarer gamma-ray burst sources of gamma rays. Pulsars have relatively long-lived magnetic fields that produce focused beams of relativistic speed charged particles, which emit gamma rays (bremsstrahlung) when those strike gas or dust in their nearby medium, and are decelerated. This is a similar mechanism to the production of high-energy photons in megavoltage radiation therapy machines (see bremsstrahlung ). Inverse Compton scattering , in which charged particles (usually electrons) impart energy to low-energy photons boosting them to higher energy photons. Such impacts of photons on relativistic charged particle beams

9504-523: The region of the event horizon of a newly formed black hole created during supernova explosion. The beam of particles moving at relativistic speeds are focused for a few tens of seconds by the magnetic field of the exploding hypernova . The fusion explosion of the hypernova drives the energetics of the process. If the narrowly directed beam happens to be pointed toward the Earth, it shines at gamma ray frequencies with such intensity, that it can be detected even at distances of up to 10 billion light years, which

9612-672: 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

9720-416: 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

9828-422: The removal of decay-causing bacteria from many foods and the prevention of the sprouting of fruit and vegetables to maintain freshness and flavor. Despite their cancer-causing properties, gamma rays are also used to treat some types of cancer , since the rays also kill cancer cells. In the procedure called gamma-knife surgery, multiple concentrated beams of gamma rays are directed to the growth in order to kill

9936-556: The rest is emitted as electromagnetic waves of all frequencies, including radio waves. The most intense sources of gamma rays, are also the most intense sources of any type of electromagnetic radiation presently known. They are the "long duration burst" sources of gamma rays in astronomy ("long" in this context, meaning a few tens of seconds), and they are rare compared with the sources discussed above. By contrast, "short" gamma-ray bursts of two seconds or less, which are not associated with supernovae, are thought to produce gamma rays during

10044-792: The shortest wavelength electromagnetic waves, typically shorter than those of X-rays . With frequencies above 30 exahertz ( 3 × 10  Hz ) and wavelengths less than 10 picometers ( 1 × 10  m ), gamma ray photons have the highest photon energy of any form of electromagnetic radiation. Paul Villard , a French chemist and physicist , discovered gamma radiation in 1900 while studying radiation emitted by radium . In 1903, Ernest Rutherford named this radiation gamma rays based on their relatively strong penetration of matter ; in 1900, he had already named two less penetrating types of decay radiation (discovered by Henri Becquerel ) alpha rays and beta rays in ascending order of penetrating power. Gamma rays from radioactive decay are in

10152-456: The star responsible for the existence of the nebula. It was identified as such in 1942, when Rudolf Minkowski found that its optical spectrum was extremely unusual. 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

10260-439: The star that exploded to produce the Crab Nebula must have had a mass of between 9 and 11  M ☉ . Stars with masses lower than 8  M ☉ 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 12  M ☉ would have produced a nebula with a different chemical composition from that observed in

10368-479: The thickness of Titan's atmosphere is 880 km (550 mi). The transit of Saturn itself could not be observed, because Chandra was passing through the Van Allen belts at the time. Gamma ray A gamma ray , also known as gamma radiation (symbol γ ), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei . It consists of

10476-516: The three types of genotoxic activity. Another study studied the effects of acute ionizing gamma radiation in rats, up to 10 Gy , and who ended up showing acute oxidative protein damage, DNA damage, cardiac troponin T carbonylation, and long-term cardiomyopathy . The natural outdoor exposure in the United Kingdom ranges from 0.1 to 0.5 μSv/h with significant increase around known nuclear and contaminated sites. Natural exposure to gamma rays

10584-574: 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

10692-813: The top of the electromagnetic spectrum in terms of energy, all extremely high-energy photons are gamma rays; for example, a photon having the Planck energy would be a gamma ray. A few gamma rays in astronomy are known to arise from gamma decay (see discussion of SN1987A ), but most do not. Photons from astrophysical sources that carry energy in the gamma radiation range are often explicitly called gamma-radiation. In addition to nuclear emissions, they are often produced by sub-atomic particle and particle-photon interactions. Those include electron-positron annihilation , neutral pion decay , bremsstrahlung , inverse Compton scattering , and synchrotron radiation . In October 2017, scientists from various European universities proposed

10800-523: The total stopping power. Because of this, a lead (high Z ) shield is 20–30% better as a gamma shield than an equal mass of another low- Z shielding material, such as aluminium, concrete, water, or soil; lead's major advantage is not in lower weight, but rather its compactness due to its higher density. Protective clothing, goggles and respirators can protect from internal contact with or ingestion of alpha or beta emitting particles, but provide no protection from gamma radiation from external sources. The higher

10908-446: The tracer, such techniques can be employed to diagnose a wide range of conditions (for example, the spread of cancer to the bones via bone scan ). Gamma rays cause damage at a cellular level and are penetrating, causing diffuse damage throughout the body. However, they are less ionising than alpha or beta particles, which are less penetrating. Low levels of gamma rays cause a stochastic health risk, which for radiation dose assessment

11016-463: The universe. Gamma-ray producing sources include supernova remnants , active galactic nuclei and pulsar wind nebulae . It also actively tests unproven theories in physics such as looking for the predicted gamma-ray annihilation signal from WIMP dark matter particles and testing Lorentz invariance predictions of loop quantum gravity . H.E.S.S. is located in the Khomas highlands of Namibia near

11124-612: Was carried out in 1989 by the Whipple Observatory 10m Gamma-Ray telescope, 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,

11232-417: Was composed of a group of stars. William Parsons, 3rd Earl of Rosse observed the nebula at Birr Castle in the early 1840s using a 36-inch (0.9 m) telescope, and made a drawing of it that showed it with arms like those of a crab. He observed it again later, in 1848, using a 72-inch (1.8 m) telescope but could not confirm the supposed resemblance, but the name stuck nevertheless. The Crab Nebula

11340-488: Was discovered by English astronomer John Bevis in 1731. It corresponds with a bright supernova recorded by Chinese astronomers in 1054 as a guest star . The nebula was the first astronomical object identified that corresponds with a historically-observed supernova explosion. 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

11448-594: Was observing a bright comet . Messier catalogued it as the first entry in his catalogue of comet-like objects; in 1757, Alexis Clairaut reexamined the calculations of Edmund Halley and predicted the return of Halley's Comet in late 1758. The exact time of the comet's return required the consideration of perturbations to its orbit caused by planets in the Solar System such as Jupiter, which Clairaut and his two colleagues Jérôme Lalande and Nicole-Reine Lepaute carried out more precisely than Halley, finding that

11556-417: Was the first astronomical object recognized as being connected to a supernova explosion. In the early twentieth century, the analysis of early photographs of the nebula taken several years apart revealed that it was expanding. Tracing the expansion back revealed that the nebula must have become visible on Earth about 900 years before. Historical records revealed that a new star bright enough to be seen in

11664-552: 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 2.0 ± 0.5 kpc (6,500 ± 1,600 ly). Along its longest visible dimension, it thus measures about 4.1 ± 1 pc (13 ± 3 ly) across. The Crab Nebula currently

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