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149-600: The objective of the mission was the observation of gamma-ray bursts , high-energy cosmic rays and transient phenomena in the Earth's upper atmosphere. The mission launch was initially planned for 2011 when 300 years since the birthday of Mikhail Lomonosov was celebrated. After several postponements the mission was finally launched on 28 April 2016 from the Vostochny Cosmodrome by the Soyuz 2.1a launch vehicle, on

298-429: A bolometric flux comparable to a bright star of our galaxy despite a distance of billions of light years (compared to a few tens of light years for most visible stars). Most of this energy is released in gamma rays, although some GRBs have extremely luminous optical counterparts as well. GRB 080319B , for example, was accompanied by an optical counterpart that peaked at a visible magnitude of 5.8, comparable to that of

447-411: A "short" population with an average duration of about 0.3 seconds and a "long" population with an average duration of about 30 seconds. Both distributions are very broad with a significant overlap region in which the identity of a given event is not clear from duration alone. Additional classes beyond this two-tiered system have been proposed on both observational and theoretical grounds. Events with

596-452: A GRB, because the oceans were mostly oligotrophic and clear. The late Ordovician species of trilobites that spent portions of their lives in the plankton layer near the ocean surface were much harder hit than deep-water dwellers, which tended to remain within quite restricted areas. This is in contrast to the usual pattern of extinction events, wherein species with more widely spread populations typically fare better. A possible explanation

745-503: A carbon–oxygen core and a companion neutron star or a black hole. Furthermore, the energy of GRBs in the model is isotropic instead of collimated. The creators of the model have noted the numerous drawbacks of the standard "fireball" model as motivation for developing the model, such as the markedly different energetics for supernova and gamma-ray bursts, and the fact that the existence of extremely narrow beaming angles have never been observationally corroborated. The closest analogs within

894-484: A collision between two objects in the Solar System. Other splitting comets include 3D/Biela in 1846 and 73P/Schwassmann–Wachmann from 1995 to 2006. Greek historian Ephorus reported that a comet split apart as far back as the winter of 372–373 BC. Comets are suspected of splitting due to thermal stress, internal gas pressure, or impact. Comets 42P/Neujmin and 53P/Van Biesbroeck appear to be fragments of

1043-731: A comet is known as the nucleus. Cometary nuclei are composed of an amalgamation of rock , dust , water ice , and frozen carbon dioxide , carbon monoxide , methane , and ammonia . As such, they are popularly described as "dirty snowballs" after Fred Whipple 's model. Comets with a higher dust content have been called "icy dirtballs". The term "icy dirtballs" arose after observation of Comet 9P/Tempel 1 collision with an "impactor" probe sent by NASA Deep Impact mission in July 2005. Research conducted in 2014 suggests that comets are like " deep fried ice cream ", in that their surfaces are formed of dense crystalline ice mixed with organic compounds , while

1192-482: A comet nucleus. Infrared imaging of Hartley 2 shows such jets exiting and carrying with it dust grains into the coma. Most comets are small Solar System bodies with elongated elliptical orbits that take them close to the Sun for a part of their orbit and then out into the further reaches of the Solar System for the remainder. Comets are often classified according to the length of their orbital periods : The longer

1341-551: A comet was seen or not. Using Edmond Halley 's records of comet sightings, however, William Whiston in 1711 wrote that the Great Comet of 1680 had a periodicity of 574 years and was responsible for the worldwide flood in the Book of Genesis , by pouring water on Earth. His announcement revived for another century fear of comets, now as direct threats to the world instead of signs of disasters. Spectroscopic analysis in 1910 found

1490-711: A crater on Comet Tempel 1 to study its interior, and the European Space Agency's Rosetta , which became the first to land a robotic spacecraft on a comet. The word comet derives from the Old English cometa from the Latin comēta or comētēs . That, in turn, is a romanization of the Greek κομήτης 'wearing long hair', and the Oxford English Dictionary notes that

1639-523: A doughnut-shaped inner cloud, the Hills cloud, of 2,000–20,000 AU (0.03–0.32 ly). The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets that fall to inside the orbit of Neptune . The inner Oort cloud is also known as the Hills cloud, named after Jack G. Hills , who proposed its existence in 1981. Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as

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1788-482: A duration of less than about two seconds are classified as short gamma-ray bursts (sGRB). These account for about 30% of gamma-ray bursts, but until 2005, no afterglow had been successfully detected from any short event and little was known about their origins. Following this, several dozen short gamma-ray burst afterglows were detected and localized, several of them associated with regions of little or no star formation, such as large elliptical galaxies . This ruled out

1937-432: A few cases particularly well-localized bursts (those whose positions were determined with what was then a high degree of accuracy) could be clearly shown to have no bright objects of any nature consistent with the position derived from the detecting satellites. This suggested an origin of either very faint stars or extremely distant galaxies. Even the most accurate positions contained numerous faint stars and galaxies, and it

2086-784: A few genuinely hyperbolic (i.e. non-periodic) trajectories, but no more than could be accounted for by perturbations from Jupiter. Comets from interstellar space are moving with velocities of the same order as the relative velocities of stars near the Sun (a few tens of km per second). When such objects enter the Solar System, they have a positive specific orbital energy resulting in a positive velocity at infinity ( v ∞ {\displaystyle v_{\infty }\!} ) and have notably hyperbolic trajectories. A rough calculation shows that there might be four hyperbolic comets per century within Jupiter's orbit, give or take one and perhaps two orders of magnitude . The Oort cloud

2235-534: A flurry of discoveries from the James Webb Space Telescope , GRB 090429B was the most distant known object in the universe. In October 2018, astronomers reported that GRB 150101B (detected in 2015) and GW170817 , a gravitational wave event detected in 2017 (which has been associated with GRB170817A, a burst detected 1.7 seconds later), may have been produced by the same mechanism – the merger of two neutron stars . The similarities between

2384-549: A gamma-ray burst in the Milky Way pointed directly at Earth would likely sterilize the planet or effect a mass extinction . The Late Ordovician mass extinction has been hypothesised by some researchers to have occurred as a result of such a gamma-ray burst. GRB signals were first detected in 1967 by the Vela satellites , which were designed to detect covert nuclear weapons tests ; after thorough declassification analysis, this

2533-420: A gamma-ray burst was one teraelectronvolt , from GRB 190114C in 2019. (Note, this is about a thousand times lower energy than the highest energy light observed from any source, which is 1.4 petaelectronvolts as of the year 2021. ) The light curves of gamma-ray bursts are extremely diverse and complex. No two gamma-ray burst light curves are identical, with large variation observed in almost every property:

2682-621: A group consisting of professional astronomers and citizen scientists in light curves recorded by the Kepler Space Telescope. After Kepler Space Telescope retired in October 2018, a new telescope called TESS Telescope has taken over Kepler's mission. Since the launch of TESS, astronomers have discovered the transits of comets around the star Beta Pictoris using a light curve from TESS. Since TESS has taken over, astronomers have since been able to better distinguish exocomets with

2831-466: A hyperbolic orbit (e > 1) when near perihelion that using a heliocentric unperturbed two-body best-fit suggests they may escape the Solar System. As of 2022 , only two objects have been discovered with an eccentricity significantly greater than one: 1I/ʻOumuamua and 2I/Borisov , indicating an origin outside the Solar System. While ʻOumuamua, with an eccentricity of about 1.2, showed no optical signs of cometary activity during its passage through

2980-416: A kilonova associated with short GRB 130603B was reported in 2013. The mean duration of sGRB events of around 200 milliseconds implied (due to causality ) that the sources must be of very small physical diameter in stellar terms: less than 0.2 light-seconds (60,000 km or 37,000 miles) – about four times the Earth's diameter. The observation of minutes to hours of X-ray flashes after an sGRB

3129-515: A lifetime of about 10,000 years or ~1,000 orbits whereas long-period comets fade much faster. Only 10% of the long-period comets survive more than 50 passages to small perihelion and only 1% of them survive more than 2,000 passages. Eventually most of the volatile material contained in a comet nucleus evaporates, and the comet becomes a small, dark, inert lump of rock or rubble that can resemble an asteroid. Some asteroids in elliptical orbits are now identified as extinct comets. Roughly six percent of

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3278-425: A link to massive stars, confirming the short events to be physically distinct from long events. In addition, there had been no association with supernovae. The true nature of these objects was thus initially unknown, but the leading hypothesis was that they originated from the mergers of binary neutron stars or a neutron star with a black hole . Such mergers were hypothesized to produce kilonovae , and evidence for

3427-641: A parent comet. Numerical integrations have shown that both comets had a rather close approach to Jupiter in January 1850, and that, before 1850, the two orbits were nearly identical. Another group of comets that is the result of fragmentation episodes is the Liller comet family made of C/1988 A1 (Liller), C/1996 Q1 (Tabur), C/2015 F3 (SWAN), C/2019 Y1 (ATLAS), and C/2023 V5 (Leonard) . Some comets have been observed to break up during their perihelion passage, including great comets West and Ikeya–Seki . Biela's Comet

3576-432: A periodic orbit (that is, all short-period comets plus all long-period comets), whereas others use it to mean exclusively short-period comets. Similarly, although the literal meaning of "non-periodic comet" is the same as "single-apparition comet", some use it to mean all comets that are not "periodic" in the second sense (that is, to include all comets with a period greater than 200 years). Early observations have revealed

3725-524: A population they are likely less collimated than long GRBs or possibly not collimated at all in some cases. Because of the immense distances of most gamma-ray burst sources from Earth, identification of the progenitors, the systems that produce these explosions, is challenging. The association of some long GRBs with supernovae and the fact that their host galaxies are rapidly star-forming offer very strong evidence that long gamma-ray bursts are associated with massive stars. The most widely accepted mechanism for

3874-411: A possible global reduction of 25–35%, with as much as 75% in certain locations, an effect that would last for years. This reduction is enough to cause a dangerously elevated UV index at the surface. Secondly, the nitrogen oxides cause photochemical smog , which darkens the sky and blocks out parts of the sunlight spectrum. This would affect photosynthesis , but models show only about a 1% reduction of

4023-486: A result of low sensitivity of current detectors to long-duration events, rather than a reflection of their true frequency. A 2013 study, on the other hand, shows that the existing evidence for a separate ultra-long GRB population with a new type of progenitor is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion. Gamma-ray bursts are very bright as observed from Earth despite their typically immense distances. An average long GRB has

4172-573: A second to tens of seconds. This ultraviolet radiation could potentially reach dangerous levels depending on the exact nature and distance of the burst, but it seems unlikely to be able to cause a global catastrophe for life on Earth. The long-term effects from a nearby burst are more dangerous. Gamma rays cause chemical reactions in the atmosphere involving oxygen and nitrogen molecules , creating first nitrogen oxide then nitrogen dioxide gas. The nitrogen oxides cause dangerous effects on three levels. First, they deplete ozone , with models showing

4321-402: A very low albedo , making them among the least reflective objects found in the Solar System. The Giotto space probe found that the nucleus of Halley's Comet (1P/Halley) reflects about four percent of the light that falls on it, and Deep Space 1 discovered that Comet Borrelly 's surface reflects less than 3.0%; by comparison, asphalt reflects seven percent. The dark surface material of

4470-480: A very small fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System (in the Oort cloud ) is about one trillion. Roughly one comet per year is visible to the naked eye , though many of those are faint and unspectacular. Particularly bright examples are called " great comets ". Comets have been visited by uncrewed probes such as NASA's Deep Impact , which blasted

4619-726: A very strong solar flare is another possibility. No gamma-ray bursts from within our own galaxy, the Milky Way , have been observed, and the question of whether one has ever occurred remains unresolved. In light of evolving understanding of gamma-ray bursts and their progenitors, the scientific literature records a growing number of local, past, and future GRB candidates. Long duration GRBs are related to superluminous supernovae, or hypernovae, and most luminous blue variables (LBVs) and rapidly spinning Wolf–Rayet stars are thought to end their life cycles in core-collapse supernovae with an associated long-duration GRB. Knowledge of GRBs, however,

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4768-542: A very young A-type main-sequence star , in 1987. A total of 11 such exocomet systems have been identified as of 2013 , using the absorption spectrum caused by the large clouds of gas emitted by comets when passing close to their star. For ten years the Kepler space telescope was responsible for searching for planets and other forms outside of the solar system. The first transiting exocomets were found in February 2018 by

4917-459: Is a 50% chance that such a lethal GRB took place within two kiloparsecs of Earth during the last 500 million years, causing one of the major mass extinction events. The major Ordovician–Silurian extinction event 450 million years ago may have been caused by a GRB. Estimates suggest that approximately 20–60% of the total phytoplankton biomass in the Ordovician oceans would have perished in

5066-484: Is a little beyond the orbit of Neptune . Comets whose aphelia are near a major planet's orbit are called its "family". Such families are thought to arise from the planet capturing formerly long-period comets into shorter orbits. At the shorter orbital period extreme, Encke's Comet has an orbit that does not reach the orbit of Jupiter, and is known as an Encke-type comet . Short-period comets with orbital periods less than 20 years and low inclinations (up to 30 degrees) to

5215-650: Is a small X-ray telescope satellite for studying the explosions of massive stars by analysing the resulting gamma-ray bursts, developed by China National Space Administration (CNSA), Chinese Academy of Sciences (CAS) and the French Space Agency ( CNES ), launched on 22 June 2024 (07:00:00 UTC). The Taiwan Space Agency is launching a cubesat called The Gamma-ray Transients Monitor to track GRBs and other bright gamma-ray transients with energies ranging from 50 keV to 2 MeV in Q4 2026. New developments since

5364-416: Is bound to the Sun with roughly a 92,600-year orbit because the eccentricity drops below 1 as it moves farther from the Sun. The future orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the Solar System . By definition long-period comets remain gravitationally bound to

5513-485: Is difficult to observe a burst's position at longer wavelengths immediately after the initial burst. The breakthrough came in February 1997 when the satellite BeppoSAX detected a gamma-ray burst ( GRB 970228 ) and when the X-ray camera was pointed towards the direction from which the burst had originated, it detected fading X-ray emission. The William Herschel Telescope identified a fading optical counterpart 20 hours after

5662-562: Is difficult. The nucleus of 322P/SOHO is probably only 100–200 meters (330–660 ft) in diameter. A lack of smaller comets being detected despite the increased sensitivity of instruments has led some to suggest that there is a real lack of comets smaller than 100 meters (330 ft) across. Known comets have been estimated to have an average density of 0.6 g/cm (0.35 oz/cu in). Because of their low mass, comet nuclei do not become spherical under their own gravity and therefore have irregular shapes. Roughly six percent of

5811-461: Is estimated that just 1% of all TDEs are jetted events. The means by which gamma-ray bursts convert energy into radiation remains poorly understood, and as of 2010 there was still no generally accepted model for how this process occurs. Any successful model of GRB emission must explain the physical process for generating gamma-ray emission that matches the observed diversity of light curves, spectra, and other characteristics. Particularly challenging

5960-404: Is followed by its de-excitation into the ground state of the ion by the emission of X-rays and far ultraviolet photons. Bow shocks form as a result of the interaction between the solar wind and the cometary ionosphere, which is created by the ionization of gases in the coma. As the comet approaches the Sun, increasing outgassing rates cause the coma to expand, and the sunlight ionizes gases in

6109-407: Is formed as a result of the ionization by solar ultra-violet radiation of particles in the coma. Once the particles have been ionized, they attain a net positive electrical charge, which in turn gives rise to an "induced magnetosphere " around the comet. The comet and its induced magnetic field form an obstacle to outward flowing solar wind particles. Because the relative orbital speed of the comet and

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6258-537: Is from metal-poor galaxies of former epochs of the universe's evolution , and it is impossible to directly extrapolate to encompass more evolved galaxies and stellar environments with a higher metallicity , such as the Milky Way. Comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun , a process called outgassing . This produces an extended, gravitationally unbound atmosphere or coma surrounding

6407-628: Is still operational. Swift is equipped with a very sensitive gamma-ray detector as well as on-board X-ray and optical telescopes, which can be rapidly and automatically slewed to observe afterglow emission following a burst. More recently, the Fermi mission was launched carrying the Gamma-Ray Burst Monitor , which detects bursts at a rate of several hundred per year, some of which are bright enough to be observed at extremely high energies with Fermi's Large Area Telescope . Meanwhile, on

6556-476: Is strong evidence that some short-duration gamma-ray bursts occur in systems with no star formation and no massive stars, such as elliptical galaxies and galaxy halos . The favored hypothesis for the origin of most short gamma-ray bursts is the merger of a binary system consisting of two neutron stars. According to this model, the two stars in a binary slowly spiral towards each other because gravitational radiation releases energy until tidal forces suddenly rip

6705-529: Is that in the course of a gravitational collapse and in reaching the event horizon of a black hole, all matter disintegrates into a burst of gamma radiation. This class of GRB-like events was first discovered through the detection of Swift J1644+57 (originally classified as GRB 110328A) by the Swift Gamma-Ray Burst Mission on 28 March 2011. This event had a gamma-ray duration of about 2 days, much longer than even ultra-long GRBs, and

6854-399: Is that trilobites remaining in deep water would be more shielded from the increased UV radiation associated with a GRB. Also supportive of this hypothesis is the fact that during the late Ordovician, burrowing bivalve species were less likely to go extinct than bivalves that lived on the surface. A case has been made that the 774–775 carbon-14 spike was the result of a short GRB, though

7003-420: Is the need to explain the very high efficiencies that are inferred from some explosions: some gamma-ray bursts may convert as much as half (or more) of the explosion energy into gamma-rays. Early observations of the bright optical counterparts to GRB 990123 and to GRB 080319B , whose optical light curves were extrapolations of the gamma-ray light spectra, have suggested that inverse Compton scattering may be

7152-442: Is thought to be released during a supernova or superluminous supernova as a high-mass star implodes to form a neutron star or a black hole . From gravitational wave observations, §   short-duration (sGRB) events describe a subclass of GRB signals that are now known to originate from the cataclysmic merger of binary neutron stars. The sources of most GRB are billions of light years away from Earth , implying that

7301-568: Is thought to occupy a vast space starting from between 2,000 and 5,000 AU (0.03 and 0.08 ly) to as far as 50,000 AU (0.79 ly) from the Sun. This cloud encases the celestial bodies that start at the middle of the Solar System—the Sun, all the way to outer limits of the Kuiper Belt. The Oort cloud consists of viable materials necessary for the creation of celestial bodies. The Solar System's planets exist only because of

7450-470: Is toxic to a variety of organisms, including amphibian life, but models predict that it would not reach levels that would cause a serious global effect. The nitrates might in fact be of benefit to some plants. All in all, a GRB within a few kiloparsecs, with its energy directed towards Earth, will mostly damage life by raising the UV levels during the burst itself and for a few years thereafter. Models show that

7599-405: Is usually associated with very high-temperature bodies . The X-rays are generated by the interaction between comets and the solar wind: when highly charged solar wind ions fly through a cometary atmosphere, they collide with cometary atoms and molecules, "stealing" one or more electrons from the atom in a process called "charge exchange". This exchange or transfer of an electron to the solar wind ion

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7748-558: The ALICE spectrograph on Rosetta determined that electrons (within 1 km (0.62 mi) above the comet nucleus ) produced from photoionization of water molecules by solar radiation , and not photons from the Sun as thought earlier, are responsible for the degradation of water and carbon dioxide molecules released from the comet nucleus into its coma. Instruments on the Philae lander found at least sixteen organic compounds at

7897-498: The German Electron Synchrotron , stating that "Our measurements show that the energy released in very-high-energy gamma-rays is comparable to the amount radiated at all lower energies taken together". Short (time duration) GRBs appear to come from a lower-redshift (i.e. less distant) population and are less luminous than long GRBs. The degree of beaming in short bursts has not been accurately measured, but as

8046-544: The Kuiper belt or its associated scattered disc , which lie beyond the orbit of Neptune . Long-period comets are thought to originate in the Oort cloud , a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun by gravitational perturbations from passing stars and the galactic tide . Hyperbolic comets may pass once through

8195-659: The Nuclear Test Ban Treaty in 1963. On July 2, 1967, at 14:19 UTC , the Vela 4 and Vela 3 satellites detected a flash of gamma radiation unlike any known nuclear weapons signature. Uncertain what had happened but not considering the matter particularly urgent, the team at the Los Alamos National Laboratory , led by Ray Klebesadel , filed the data away for investigation. As additional Vela satellites were launched with better instruments,

8344-468: The asteroid belt . Because their elliptical orbits frequently take them close to the giant planets, comets are subject to further gravitational perturbations . Short-period comets have a tendency for their aphelia to coincide with a giant planet 's semi-major axis, with the JFCs being the largest group. It is clear that comets coming in from the Oort cloud often have their orbits strongly influenced by

8493-460: The ionosphere of the planet Venus streams outwards in a manner similar to the ion tail seen streaming from a comet under similar conditions." Uneven heating can cause newly generated gases to break out of a weak spot on the surface of comet's nucleus, like a geyser. These streams of gas and dust can cause the nucleus to spin, and even split apart. In 2010 it was revealed dry ice (frozen carbon dioxide) can power jets of material flowing out of

8642-460: The near-Earth asteroids are thought to be the extinct nuclei of comets that no longer experience outgassing, including 14827 Hypnos and 3552 Don Quixote . Results from the Rosetta and Philae spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals . Further,

8791-426: The 1982 perihelion passage, but a 1980 encounter with Jupiter accelerated the comet giving it the largest eccentricity (1.057) of any known solar comet with a reasonable observation arc. Comets not expected to return to the inner Solar System include C/1980 E1 , C/2000 U5 , C/2001 Q4 (NEAT) , C/2009 R1 , C/1956 R1 , and C/2007 F1 (LONEOS). Some authorities use the term "periodic comet" to refer to any comet with

8940-400: The 2000s include the recognition of short gamma-ray bursts as a separate class (likely from merging neutron stars and not associated with supernovae), the discovery of extended, erratic flaring activity at X-ray wavelengths lasting for many minutes after most GRBs, and the discovery of the most luminous ( GRB 080319B ) and the former most distant ( GRB 090423 ) objects in the universe. Prior to

9089-498: The Earth and never be detected. When a gamma-ray burst is pointed towards Earth, the focusing of its energy along a relatively narrow beam causes the burst to appear much brighter than it would have been were its energy emitted spherically. The total energy of typical gamma-ray bursts has been estimated at 3 × 10  J, – which is larger than the total energy (10  J) of ordinary supernovae (type Ia , Ibc , II ), with gamma-ray bursts also being more powerful than

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9238-517: The GRB having originated in star-forming regions. In December 2022, astronomers reported the observation of GRB 211211A for 51 seconds, the first evidence of a long GRB produced by a neutron star merger . Following this, GRB 191019A (2019, 64s) and GRB 230307A (2023, 35s) have been argued to signify an emerging class of long GRBs which originate from neutron star mergers. ulGRB are defined as GRB lasting more than 10,000 seconds, covering

9387-461: The Los Alamos team continued to find inexplicable gamma-ray bursts in their data. By analyzing the different arrival times of the bursts as detected by different satellites, the team was able to determine rough estimates for the sky positions of 16 bursts and definitively rule out a terrestrial or solar origin. Contrary to popular belief, the data was never classified. After thorough analysis,

9536-518: The Milky Way galaxy and have been harmless to Earth. However, if a GRB were to occur within the Milky Way within 5,000 to 8,000 light-years and its emission were beamed straight towards Earth, the effects could be harmful and potentially devastating for its ecosystems . Currently, orbiting satellites detect on average approximately one GRB per day. The closest observed GRB as of March 2014 was GRB 980425 , located 40 megaparsecs (130,000,000 ly) away ( z =0.0085) in an SBc-type dwarf galaxy. GRB 980425

9685-539: The Milky Way galaxy of the stars producing long gamma-ray bursts are likely the Wolf–Rayet stars , extremely hot and massive stars, which have shed most or all of their hydrogen envelope. Eta Carinae , Apep , and WR 104 have been cited as possible future gamma-ray burst progenitors. It is unclear if any star in the Milky Way has the appropriate characteristics to produce a gamma-ray burst. The massive-star model probably does not explain all types of gamma-ray burst. There

9834-460: The Russian space program lost both of its scientific satellites until the launch of Spektr-RG in July 2019. The satellite decayed from orbit on 16 December 2023. Gamma-ray burst In gamma-ray astronomy , gamma-ray bursts ( GRBs ) are immensely energetic events occurring in distant galaxies which represent the brightest and "most powerful class of explosions [ sic ] in

9983-514: The Solar System, such as Jupiter. An example of this is Comet C/1980 E1 , which was shifted from an orbit of 7.1 million years around the Sun, to a hyperbolic trajectory, after a 1980 close pass by the planet Jupiter. Interstellar comets such as 1I/ʻOumuamua and 2I/Borisov never orbited the Sun and therefore do not require a 3rd-body interaction to be ejected from the Solar System. Jupiter-family comets and long-period comets appear to follow very different fading laws. The JFCs are active over

10132-416: The Sun because this gas is more strongly affected by the solar wind than is dust, following magnetic field lines rather than an orbital trajectory. On occasions—such as when Earth passes through a comet's orbital plane, the antitail , pointing in the opposite direction to the ion and dust tails, may be seen. The observation of antitails contributed significantly to the discovery of solar wind. The ion tail

10281-455: The Sun, outgassing of its icy components releases solid debris too large to be swept away by radiation pressure and the solar wind. If Earth's orbit sends it through that trail of debris, which is composed mostly of fine grains of rocky material, there is likely to be a meteor shower as Earth passes through. Denser trails of debris produce quick but intense meteor showers and less dense trails create longer but less intense showers. Typically,

10430-410: The Sun. The coma is generally made of water and dust, with water making up to 90% of the volatiles that outflow from the nucleus when the comet is within 3 to 4 astronomical units (450,000,000 to 600,000,000 km; 280,000,000 to 370,000,000 mi) of the Sun. The H 2 O parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization , with

10579-407: The Sun. At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, and in doing so enlarging the tail. Ion tails have been observed to extend one astronomical unit (150 million km) or more. Both the coma and tail are illuminated by the Sun and may become visible when a comet passes through the inner Solar System, the dust reflects sunlight directly while

10728-412: The Sun. For example, about a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun. The Great Comet of 1811 had a coma roughly the diameter of the Sun. Even though the coma can become quite large, its size can decrease about the time it crosses the orbit of Mars around 1.5 astronomical units (220,000,000 km; 140,000,000 mi) from

10877-676: The Sun; those comets that are ejected from the Solar System due to close passes by major planets are no longer properly considered as having "periods". The orbits of long-period comets take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic. Long-period comets such as C/1999 F1 and C/2017 T2 (PANSTARRS) can have aphelion distances of nearly 70,000 AU (0.34 pc; 1.1 ly) with orbital periods estimated around 6 million years. Single-apparition or non-periodic comets are similar to long-period comets because they have parabolic or slightly hyperbolic trajectories when near perihelion in

11026-444: The beam) can be estimated directly by observing the achromatic "jet breaks" in afterglow light curves: a time after which the slowly decaying afterglow begins to fade rapidly as the jet slows and can no longer beam its radiation as effectively. Observations suggest significant variation in the jet angle from between 2 and 20 degrees. Because their energy is strongly focused, the gamma rays emitted by most bursts are expected to miss

11175-431: The bow shocks already were fully developed. The Rosetta spacecraft observed the bow shock at comet 67P/Churyumov–Gerasimenko at an early stage of bow shock development when the outgassing increased during the comet's journey toward the Sun. This young bow shock was called the "infant bow shock". The infant bow shock is asymmetric and, relative to the distance to the nucleus, wider than fully developed bow shocks. In

11324-553: The burst. Once the GRB faded, deep imaging was able to identify a faint, distant host galaxy at the location of the GRB as pinpointed by the optical afterglow. Because of the very faint luminosity of this galaxy, its exact distance was not measured for several years. Well after then, another major breakthrough occurred with the next event registered by BeppoSAX, GRB 970508 . This event was localized within four hours of its discovery, allowing research teams to begin making observations much sooner than any previous burst. The spectrum of

11473-427: The case of Oort cloud objects) may throw one of these bodies into an elliptical orbit that takes it inwards toward the Sun to form a visible comet. Unlike the return of periodic comets, whose orbits have been established by previous observations, the appearance of new comets by this mechanism is unpredictable. When flung into the orbit of the sun, and being continuously dragged towards it, tons of matter are stripped from

11622-439: The coma. When the solar wind passes through this ion coma, the bow shock appears. The first observations were made in the 1980s and 1990s as several spacecraft flew by comets 21P/Giacobini–Zinner , 1P/Halley, and 26P/Grigg–Skjellerup . It was then found that the bow shocks at comets are wider and more gradual than the sharp planetary bow shocks seen at, for example, Earth. These observations were all made near perihelion when

11771-410: The comet's surface, four of which ( acetamide , acetone , methyl isocyanate and propionaldehyde ) have been detected for the first time on a comet. The streams of dust and gas thus released form a huge and extremely thin atmosphere around the comet called the "coma". The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous "tail" to form pointing away from

11920-498: The comets which greatly influence their lifetime; the more stripped, the shorter they live and vice versa. Long-period comets have highly eccentric orbits and periods ranging from 200 years to thousands or even millions of years. An eccentricity greater than 1 when near perihelion does not necessarily mean that a comet will leave the Solar System. For example, Comet McNaught had a heliocentric osculating eccentricity of 1.000019 near its perihelion passage epoch in January 2007 but

12069-481: The density of the debris trail is related to how long ago the parent comet released the material. The Perseid meteor shower , for example, occurs every year between 9 and 13 August, when Earth passes through the orbit of Comet Swift–Tuttle . Halley's Comet is the source of the Orionid shower in October. Many comets and asteroids collided with Earth in its early stages. Many scientists think that comets bombarding

12218-464: The destructive effects of this increase can cause up to 16 times the normal levels of DNA damage. It has proved difficult to assess a reliable evaluation of the consequences of this on the terrestrial ecosystem, because of the uncertainty in biological field and laboratory data. There is a very good chance (but no certainty) that at least one lethal GRB took place during the past 5 billion years close enough to Earth as to significantly damage life. There

12367-409: The development of a number of additional instruments designed specifically to explore the nature of GRBs, especially in the earliest moments following the explosion. The first such mission, HETE-2 , was launched in 2000 and functioned until 2006, providing most of the major discoveries during this period. One of the most successful space missions to date, Swift , was launched in 2004 and as of May 2024

12516-495: The dimmest naked-eye stars despite the burst's distance of 7.5 billion light years. This combination of brightness and distance implies an extremely energetic source. Assuming the gamma-ray explosion to be spherical, the energy output of GRB 080319B would be within a factor of two of the rest-mass energy of the Sun (the energy which would be released were the Sun to be converted entirely into radiation). Gamma-ray bursts are thought to be highly focused explosions, with most of

12665-513: The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets . In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were called Manx comets . They are still classified as comets, such as C/2014 S3 (PANSTARRS). Twenty-seven Manx comets were found from 2013 to 2017. As of November 2021 , there are 4,584 known comets. However, this represents

12814-399: The discovery of GRBs, astronomers searched for a counterpart at other wavelengths: i.e., any astronomical object in positional coincidence with a recently observed burst. Astronomers considered many distinct classes of objects, including white dwarfs , pulsars , supernovae , globular clusters , quasars , Seyfert galaxies , and BL Lac objects . All such searches were unsuccessful, and in

12963-472: The distribution of GRBs is isotropic  – not biased towards any particular direction in space. If the sources were from within our own galaxy, they would be strongly concentrated in or near the galactic plane. The absence of any such pattern in the case of GRBs provided strong evidence that gamma-ray bursts must come from beyond the Milky Way. However, some Milky Way models are still consistent with an isotropic distribution. For decades after

13112-400: The dominant process in some events. In this model, pre-existing low-energy photons are scattered by relativistic electrons within the explosion, augmenting their energy by a large factor and transforming them into gamma-rays. The nature of the longer-wavelength afterglow emission (ranging from X-ray through radio ) that follows gamma-ray bursts is better understood. Any energy released by

13261-667: The duration of observable emission can vary from milliseconds to tens of minutes, there can be a single peak or several individual subpulses, and individual peaks can be symmetric or with fast brightening and very slow fading. Some bursts are preceded by a " precursor " event, a weak burst that is then followed (after seconds to minutes of no emission at all) by the much more intense "true" bursting episode. The light curves of some events have extremely chaotic and complicated profiles with almost no discernible patterns. Although some light curves can be roughly reproduced using certain simplified models, little progress has been made in understanding

13410-424: The ecliptic are called traditional Jupiter-family comets (JFCs). Those like Halley, with orbital periods of between 20 and 200 years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets (HTCs). As of 2023 , 70 Encke-type comets, 100 HTCs, and 755 JFCs have been reported. Recently discovered main-belt comets form a distinct class, orbiting in more circular orbits within

13559-686: The existence of tektites and australites . Fear of comets as acts of God and signs of impending doom was highest in Europe from AD 1200 to 1650. The year after the Great Comet of 1618 , for example, Gotthard Arthusius published a pamphlet stating that it was a sign that the Day of Judgment was near. He listed ten pages of comet-related disasters, including "earthquakes, floods, changes in river courses, hail storms, hot and dry weather, poor harvests, epidemics, war and treason and high prices". By 1700 most scholars concluded that such events occurred whether

13708-417: The explosion energy collimated into a narrow jet . The jets of gamma-ray bursts are ultrarelativistic , and are the most relativistic jets in the universe. The matter in gamma-ray burst jets may also become superluminal , or faster than the speed of light in the jet medium, with there also being effects of time reversibility . The approximate angular width of the jet (that is, the degree of spread of

13857-412: The explosion not radiated away in the burst itself takes the form of matter or energy moving outward at nearly the speed of light. As this matter collides with the surrounding interstellar gas , it creates a relativistic shock wave that then propagates forward into interstellar space. A second shock wave, the reverse shock, may propagate back into the ejected matter. Extremely energetic electrons within

14006-446: The explosions are both extremely energetic (a typical burst releases as much energy in a few seconds as the Sun will in its entire 10-billion-year lifetime) and extremely rare (a few per galaxy per million years). All GRBs in recorded history have originated from outside the Milky Way galaxy , although a related class of phenomena, soft gamma repeaters , are associated with magnetars within our galaxy. This may be self-evident, since

14155-401: The extreme isotropic energy totals as being true, with there being no need to correct for beaming. They also note that the extreme beaming angles in the standard "fireball" model have never been physically corroborated. With the discovery of GRB 190114C , astronomers may have been missing half of the total energy that gamma-ray bursts produce, with Konstancja Satalecka, an astrophysicist at

14304-574: The findings were published in 1973 as an Astrophysical Journal article entitled "Observations of Gamma-Ray Bursts of Cosmic Origin". Most early hypotheses of gamma-ray bursts posited nearby sources within the Milky Way Galaxy . From 1991, the Compton Gamma Ray Observatory (CGRO) and its Burst and Transient Source Explorer ( BATSE ) instrument, an extremely sensitive gamma-ray detector, provided data that showed

14453-494: The first launch from new cosmodrome. The spacecraft is equipped with seven scientific instruments: The TUS-telescope aboard Lomonosov stopped data collection in late 2017. On June 30, 2018, it was published that the Lomonosov-satellite had suffered a malfunction in its data transmission system. Attempts to fix the problem were underway, but fixing the problem had so far been unsuccessful. As of 14 January 2019,

14602-431: The full diversity observed. Many classification schemes have been proposed, but these are often based solely on differences in the appearance of light curves and may not always reflect a true physical difference in the progenitors of the explosions. However, plots of the distribution of the observed duration for a large number of gamma-ray bursts show a clear bimodality , suggesting the existence of two separate populations:

14751-508: The galaxies and supernovae associated with the bursts—clarified the distance and luminosity of GRBs, definitively placing them in distant galaxies. Gamma-ray bursts were first observed in the late 1960s by the U.S. Vela satellites, which were built to detect gamma radiation pulses emitted by nuclear weapons tested in space. The United States suspected that the Soviet Union might attempt to conduct secret nuclear tests after signing

14900-468: The galaxy have been observed to affect the Earth's atmosphere. Earth's atmosphere is very effective at absorbing high energy electromagnetic radiation such as x-rays and gamma rays, so these types of radiation would not reach any dangerous levels at the surface during the burst event itself. The immediate effect on life on Earth from a GRB within a few kilo parsecs would only be a short increase in ultraviolet radiation at ground level, lasting from less than

15049-486: The gases glow from ionisation . Most comets are too faint to be visible without the aid of a telescope , but a few each decade become bright enough to be visible to the naked eye. Occasionally a comet may experience a huge and sudden outburst of gas and dust, during which the size of the coma greatly increases for a period of time. This happened in 2007 to Comet Holmes . In 1996, comets were found to emit X-rays . This greatly surprised astronomers because X-ray emission

15198-433: The gravity of giant planets as a result of a close encounter. Jupiter is the source of the greatest perturbations, being more than twice as massive as all the other planets combined. These perturbations can deflect long-period comets into shorter orbital periods. Based on their orbital characteristics, short-period comets are thought to originate from the centaurs and the Kuiper belt/ scattered disc —a disk of objects in

15347-495: The ground, numerous optical telescopes have been built or modified to incorporate robotic control software that responds immediately to signals sent through the Gamma-ray Burst Coordinates Network . This allows the telescopes to rapidly repoint towards a GRB, often within seconds of receiving the signal and while the gamma-ray emission itself is still ongoing. The Space Variable Objects Monitor

15496-431: The inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition. Extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. However,

15645-405: The inner Solar System in October 2017, changes to its trajectory—which suggests outgassing —indicate that it is probably a comet. On the other hand, 2I/Borisov, with an estimated eccentricity of about 3.36, has been observed to have the coma feature of comets, and is considered the first detected interstellar comet . Comet C/1980 E1 had an orbital period of roughly 7.1 million years before

15794-429: The inner Solar System. However, gravitational perturbations from giant planets cause their orbits to change. Single-apparition comets have a hyperbolic or parabolic osculating orbit which allows them to permanently exit the Solar System after a single pass of the Sun. The Sun's Hill sphere has an unstable maximum boundary of 230,000 AU (1.1 pc; 3.6 ly). Only a few hundred comets have been seen to reach

15943-429: The interior ice is colder and less dense. The surface of the nucleus is generally dry, dusty or rocky, suggesting that the ices are hidden beneath a surface crust several metres thick. The nuclei contains a variety of organic compounds, which may include methanol , hydrogen cyanide , formaldehyde , ethanol , ethane , and perhaps more complex molecules such as long-chain hydrocarbons and amino acids . In 2009, it

16092-472: The majority of the population and because they tend to have the brightest afterglows, they have been observed in much greater detail than their short counterparts. Almost every well-studied long gamma-ray burst has been linked to a galaxy with rapid star formation, and in many cases to a core-collapse supernova as well, unambiguously associating long GRBs with the deaths of massive stars. Long GRB afterglow observations, at high redshift, are also consistent with

16241-468: The near-Earth asteroids are thought to be extinct comet nuclei. The nucleus of some comets may be fragile, a conclusion supported by the observation of comets splitting apart. A significant cometary disruption was that of Comet Shoemaker–Levy 9 , which was discovered in 1993. A close encounter in July 1992 had broken it into pieces, and over a period of six days in July 1994, these pieces fell into Jupiter's atmosphere—the first time astronomers had observed

16390-511: The neutron stars apart and they collapse into a single black hole. The infall of matter into the new black hole produces an accretion disk and releases a burst of energy, analogous to the collapsar model. Numerous other models have also been proposed to explain short gamma-ray bursts, including the merger of a neutron star and a black hole, the accretion-induced collapse of a neutron star, or the evaporation of primordial black holes . An alternative explanation proposed by Friedwardt Winterberg

16539-437: The nucleus may consist of complex organic compounds. Solar heating drives off lighter volatile compounds , leaving behind larger organic compounds that tend to be very dark, like tar or crude oil . The low reflectivity of cometary surfaces causes them to absorb the heat that drives their outgassing processes. Comet nuclei with radii of up to 30 kilometers (19 mi) have been observed, but ascertaining their exact size

16688-429: The nucleus, and sometimes a tail of gas and dust gas blown out from the coma. These phenomena are due to the effects of solar radiation and the outstreaming solar wind plasma acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while

16837-522: The object revealed a redshift of z  = 0.835, placing the burst at a distance of roughly 6 billion  light years from Earth. This was the first accurate determination of the distance to a GRB, and together with the discovery of the host galaxy of 970228 proved that GRBs occur in extremely distant galaxies. Within a few months, the controversy about the distance scale ended: GRBs were extragalactic events originating within faint galaxies at enormous distances. The following year, GRB 980425

16986-413: The origin of long-duration GRBs is the collapsar model, in which the core of an extremely massive, low- metallicity , rapidly rotating star collapses into a black hole in the final stages of its evolution . Matter near the star's core rains down towards the center and swirls into a high-density accretion disk . The infall of this material into a black hole drives a pair of relativistic jets out along

17135-477: The outer Solar System , comets remain frozen and inactive and are extremely difficult or impossible to detect from Earth due to their small size. Statistical detections of inactive comet nuclei in the Kuiper belt have been reported from observations by the Hubble Space Telescope but these detections have been questioned. As a comet approaches the inner Solar System, solar radiation causes

17284-464: The outer halo; it is seen as a possible source of new comets that resupply the relatively tenuous outer cloud as the latter's numbers are gradually depleted. The Hills cloud explains the continued existence of the Oort cloud after billions of years. Exocomets beyond the Solar System have been detected and may be common in the Milky Way . The first exocomet system detected was around Beta Pictoris ,

17433-399: The outgassings of comet 67P, suggesting that the molecule may occur more often than had been thought, and thus less an indicator of life as has been supposed. It is suspected that comet impacts have, over long timescales, delivered significant quantities of water to Earth's Moon , some of which may have survived as lunar ice . Comet and meteoroid impacts are thought to be responsible for

17582-413: The period the more elongated the ellipse. Periodic comets or short-period comets are generally defined as those having orbital periods of less than 200 years. They usually orbit more-or-less in the ecliptic plane in the same direction as the planets. Their orbits typically take them out to the region of the outer planets ( Jupiter and beyond) at aphelion ; for example, the aphelion of Halley's Comet

17731-504: The planetesimals (chunks of leftover space that assisted in the creation of planets) that were condensed and formed by the gravity of the Sun. The eccentric made from these trapped planetesimals is why the Oort Cloud even exists. Some estimates place the outer edge at between 100,000 and 200,000 AU (1.58 and 3.16 ly). The region can be subdivided into a spherical outer Oort cloud of 20,000–50,000 AU (0.32–0.79 ly), and

17880-496: The point where, at some distance along the ion tail, magnetic reconnection occurs. This leads to a "tail disconnection event". This has been observed on a number of occasions, one notable event being recorded on 20 April 2007, when the ion tail of Encke's Comet was completely severed while the comet passed through a coronal mass ejection . This event was observed by the STEREO space probe . In 2013, ESA scientists reported that

18029-553: The problems had not been solved and all the scientific equipment of the satellite were powered off. The recovery attempts continued (some systems of the satellite were responsive, the problem was with scientific payload systems). Before succumbing to these difficulties, the satellite had worked for one and a half years for its intended purpose. With the failure of the Lomonosov satellite and the Spektr-R end of mission on 30 May 2019,

18178-410: The rotational axis, which pummel through the stellar envelope and eventually break through the stellar surface and radiate as gamma rays. Some alternative models replace the black hole with a newly formed magnetar , although most other aspects of the model (the collapse of the core of a massive star and the formation of relativistic jets) are the same. However, a new model which has gained support and

18327-512: The shock wave are accelerated by strong local magnetic fields and radiate as synchrotron emission across most of the electromagnetic spectrum . This model has generally been successful in modeling the behavior of many observed afterglows at late times (generally, hours to days after the explosion), although there are difficulties explaining all features of the afterglow very shortly after the gamma-ray burst has occurred. Gamma ray bursts can have harmful or destructive effects on life. Considering

18476-429: The solar wind is supersonic, a bow shock is formed upstream of the comet in the flow direction of the solar wind. In this bow shock, large concentrations of cometary ions (called "pick-up ions") congregate and act to "load" the solar magnetic field with plasma, such that the field lines "drape" around the comet forming the ion tail. If the ion tail loading is sufficient, the magnetic field lines are squeezed together to

18625-443: The solar wind playing a minor role in the destruction of water compared to photochemistry . Larger dust particles are left along the comet's orbital path whereas smaller particles are pushed away from the Sun into the comet's tail by light pressure . Although the solid nucleus of comets is generally less than 60 kilometers (37 mi) across, the coma may be thousands or millions of kilometers across, sometimes becoming larger than

18774-425: The spectroscopic method. New planets are detected by the white light curve method which is viewed as a symmetrical dip in the charts readings when a planet overshadows its parent star. However, after further evaluation of these light curves, it has been discovered that the asymmetrical patterns of the dips presented are caused by the tail of a comet or of hundreds of comets. As a comet is heated during close passes to

18923-517: The tail may stretch beyond one astronomical unit . If sufficiently close and bright, a comet may be seen from Earth without the aid of a telescope and can subtend an arc of up to 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions. Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods , ranging from several years to potentially several millions of years. Short-period comets originate in

19072-575: The term ( ἀστὴρ ) κομήτης already meant 'long-haired star, comet' in Greek. Κομήτης was derived from κομᾶν ( koman ) 'to wear the hair long', which was itself derived from κόμη ( komē ) 'the hair of the head' and was used to mean 'the tail of a comet'. The astronomical symbol for comets (represented in Unicode ) is U+2604 ☄ COMET , consisting of a small disc with three hairlike extensions. The solid, core structure of

19221-401: The total sunlight spectrum, lasting a few years. However, the smog could potentially cause a cooling effect on Earth's climate, producing a "cosmic winter" (similar to an impact winter , but without an impact), but only if it occurs simultaneously with a global climate instability. Thirdly, the elevated nitrogen dioxide levels in the atmosphere would wash out and produce acid rain . Nitric acid

19370-414: The toxic gas cyanogen in the tail of Halley's Comet, causing panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public. If a comet is traveling fast enough, it may leave the Solar System. Such comets follow the open path of a hyperbola, and as such, they are called hyperbolic comets. Solar comets are only known to be ejected by interacting with another object in

19519-493: The trans-Neptunian region—whereas the source of long-period comets is thought to be the far more distant spherical Oort cloud (after the Dutch astronomer Jan Hendrik Oort who hypothesized its existence). Vast swarms of comet-like bodies are thought to orbit the Sun in these distant regions in roughly circular orbits. Occasionally the gravitational influence of the outer planets (in the case of Kuiper belt objects) or nearby stars (in

19668-426: The two events, in terms of gamma ray , optical , and x-ray emissions, as well as to the nature of the associated host galaxies , were considered "striking", suggesting the two separate events may both be the result of the merger of neutron stars, and both may be a kilonova , which may be more common in the universe than previously understood, according to the researchers. The highest energy light observed from

19817-475: The typical supernova. Very bright supernovae have been observed to accompany several of the nearest GRBs. Further support for focusing of the output of GRBs comes from observations of strong asymmetries in the spectra of nearby type Ic supernovae and from radio observations taken long after bursts when their jets are no longer relativistic. However, a competing model, the binary-driven hypernova model, developed by Remo Ruffini and others at ICRANet , accepts

19966-506: The universe as a whole, the safest environments for life similar to that on Earth are the lowest density regions in the outskirts of large galaxies. Our knowledge of galaxy types and their distribution suggests that life as we know it can only exist in about 10% of all galaxies. Furthermore, galaxies with a redshift, z , higher than 0.5 are unsuitable for life as we know it, because of their higher rate of GRBs and their stellar compactness. All GRBs observed to date have occurred well outside

20115-528: The universe." These extreme electromagnetic events are second only to the Big Bang as the most energetic and luminous phenomenon ever known. Gamma-ray bursts can last from ten milliseconds to several hours. After the initial flash of gamma rays , a longer-lived § Afterglow is emitted, usually in the longer wavelengths of X-ray , ultraviolet , optical , infrared , microwave or radio frequencies. The intense radiation of most observed GRBs

20264-473: The unknown degree of collimation, but are probably comparable. Since GRBs are thought to involve beamed emission along two jets in opposing directions, only planets in the path of these jets would be subjected to the high energy gamma radiation. A GRB would be able to vaporize anything in its beams out to around 200 light-years. Although nearby GRBs hitting Earth with a destructive shower of gamma rays are only hypothetical events, high energy processes across

20413-451: The upper range to the limit of the GRB duration distribution. They have been proposed to form a separate class, caused by the collapse of a blue supergiant star , a tidal disruption event or a new-born magnetar . Only a small number have been identified to date, their primary characteristic being their gamma ray emission duration. The most studied ultra-long events include GRB 101225A and GRB 111209A . The low detection rate may be

20562-448: The volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet's orbit in such a manner that it often forms a curved tail called the type II or dust tail. At the same time, the ion or type I tail, made of gases, always points directly away from

20711-446: The young Earth about 4 billion years ago brought the vast quantities of water that now fill Earth's oceans, or at least a significant portion of it. Others have cast doubt on this idea. The detection of organic molecules, including polycyclic aromatic hydrocarbons , in significant quantities in comets has led to speculation that comets or meteorites may have brought the precursors of life—or even life itself—to Earth. In 2013 it

20860-400: Was confirmed that the amino acid glycine had been found in the comet dust recovered by NASA's Stardust mission . In August 2011, a report, based on NASA studies of meteorites found on Earth, was published suggesting DNA and RNA components ( adenine , guanine , and related organic molecules) may have been formed on asteroids and comets. The outer surfaces of cometary nuclei have

21009-589: Was detected in many frequencies for months and years after. It occurred at the center of a small elliptical galaxy at redshift 3.8 billion light years away. This event has been accepted as a tidal disruption event (TDE), where a star wanders too close to a supermassive black hole , shredding the star. In the case of Swift J1644+57, an astrophysical jet traveling at near the speed of light was launched, and lasted roughly 1.5 years before turning off. Since 2011, only 4 jetted TDEs have been discovered, of which 3 were detected in gamma-rays (including Swift J1644+57). It

21158-459: Was developed by the Italian astrophysicist Remo Ruffini and other scientists at ICRANet is that of the binary-driven hypernova (BdHN) model. The model succeeds and improves upon both the fireshell model and the induced gravitational collapse (IGC) paradigm suggested before, and explains all aspects of gamma-ray bursts. The model posits long gamma-ray bursts as occurring in binary systems with

21307-577: Was far less energetic than the average GRB and was associated with the Type Ib supernova SN 1998bw . Estimating the exact rate at which GRBs occur is difficult; for a galaxy of approximately the same size as the Milky Way , estimates of the expected rate (for long-duration GRBs) can range from one burst every 10,000 years, to one burst every 1,000,000 years. Only a small percentage of these would be beamed towards Earth. Estimates of rate of occurrence of short-duration GRBs are even more uncertain because of

21456-492: Was finally conclusively established in 2017, when short GRB 170817A co-occurred with the detection of gravitational wave GW170817 , a signal from the merger of two neutron stars. Unrelated to these cataclysmic origins, short-duration gamma-ray signals are also produced by giant flares from soft gamma repeaters in nearby galaxies. Most observed events (70%) have a duration of greater than two seconds and are classified as long gamma-ray bursts. Because these events constitute

21605-408: Was followed within a day by a bright supernova ( SN 1998bw ), coincident in location, indicating a clear connection between GRBs and the deaths of very massive stars. This burst provided the first strong clue about the nature of the systems that produce GRBs. BeppoSAX functioned until 2002 and CGRO (with BATSE) was deorbited in 2000. However, the revolution in the study of gamma-ray bursts motivated

21754-485: Was published as academic research in 1973. Following their discovery, hundreds of theoretical models were proposed to explain these bursts, such as collisions between comets and neutron stars . Little information was available to verify these models until the 1997 detection of the first X-ray and optical afterglows and direct measurement of their redshifts using optical spectroscopy , and thus their distances and energy outputs. These discoveries—and subsequent studies of

21903-424: Was seen as consistent with small particles of a precursor object like a neutron star initially being swallowed by a black hole in less than two seconds, followed by some hours of lower-energy events as remaining fragments of tidally disrupted neutron star material (no longer neutronium ) would remain in orbit, spiraling into the black hole over a longer period of time. The origin of short gamma-ray bursts in kilonovae

22052-475: Was suggested that impacts between rocky and icy surfaces, such as comets, had the potential to create the amino acids that make up proteins through shock synthesis . The speed at which the comets entered the atmosphere, combined with the magnitude of energy created after initial contact, allowed smaller molecules to condense into the larger macro-molecules that served as the foundation for life. In 2015, scientists found significant amounts of molecular oxygen in

22201-466: Was widely agreed that final resolution of the origins of cosmic gamma-ray bursts would require both new satellites and faster communication. Several models for the origin of gamma-ray bursts postulated that the initial burst of gamma rays should be followed by afterglow : slowly fading emission at longer wavelengths created by collisions between the burst ejecta and interstellar gas. Early searches for this afterglow were unsuccessful, largely because it

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