# Tidal disruption event

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A tidal disruption event (TDE) is an astronomical phenomenon that occurs when a star approaches sufficiently close to a supermassive black hole (SMBH) and is pulled apart by the black hole's tidal force, experiencing spaghettification. [1] [2] A portion of the star's mass can be captured into an accretion disk around the black hole, resulting in a temporary flare of electromagnetic radiation as matter in the disk is consumed by the black hole. According to early papers, tidal disruption events should be an inevitable consequence of massive black holes' activity hidden in galaxy nuclei, whereas later theorists concluded that the resulting explosion or flare of radiation from the accretion of the stellar debris could be a unique signpost for the presence of a dormant black hole in the center of a normal galaxy. [3] Sometimes a star can survive the encounter with an SMBH, and a remnant is formed. These events are termed partial TDEs. [4]

## History

Physicist John A. Wheeler suggested that the breakup of a star in the ergosphere of a rotating black hole could induce acceleration of the released gas to relativistic speeds by the so-called "tube of toothpaste effect". [5] Wheeler succeeded in applying the relativistic generalization of the classical Newtonian tidal disruption problem to the neighbourhood of a Schwarzschild or Kerr black hole. However, these early works restricted their attention to incompressible star models and/or to stars penetrating slightly into the Roche radius, conditions in which the tides would have small amplitude.

In 1976, astronomers Juhan Frank and Martin J. Rees of the Cambridge Institute of Astronomy explored the possibility of black holes at the centers of galaxies and globular clusters, defining a critical radius under which stars are disturbed and swallowed by the black hole, suggesting that it is possible to observe these events in certain galaxies. [6] But at the time, the English researchers did not propose any precise model or simulation.

This speculative prediction and this lack of theoretical tools aroused the curiosity of Jean-Pierre Luminet and Brandon Carter of the Paris Observatory in the early 1980s who invented the concept of TDE. Their first works were published in 1982 in the journal Nature [7] and 1983 in Astronomy & Astrophysics. [8] The authors had managed to describe the tidal disturbances in the heart of Active Galactic Nuclei (AGNs) based on the "stellar pancake outbreak" model to use Luminet's expression, a model describing the tide field generated by a supermassive black hole, and the effect they called the "pancake detonation" to qualify the radiation outbreak resulting from these disturbances. Later, in 1986, Luminet and Carter published in the journal Astrophysical Journal Supplement an analysis covering all the cases of TDE and not only the 10% producing "spaghettifications" and other "pancakes flambées". [9]

It was only a decade later, in 1990, that the first TDE-compliant candidates were detected through "All Sky" X-ray survey of DLR's/NASA's ROSAT satellite. [10] Since then, more than a dozen candidates have been discovered, including more active sources in ultraviolet or visible for a reason that remained mysterious.

## Discovery

Finally, the theory of Luminet and Carter was confirmed by the observation of spectacular eruptions resulting from the accretion of stellar debris by a massive object located in the heart of the AGN (e.g. NGC 5128 or NGC 4438) but also in the heart of the Milky Way (Sgr A *). The TDE theory even explains the superluminous supernova SN 2015L, better known by the code name ASASSN-15lh, a supernova that exploded just before being absorbed beneath the horizon of a massive black hole.

Today, all known TDEs and TDE candidates have been listed in "The Open TDE Catalog" [11] run by the Harvard CfA, which has had 91 entries since 1999.

## New observations

In September 2016, a team from the University of Science and Technology of China in Hefei, Anhui, China, announced that using data from NASA 's Wide-field Infrared Survey Explorer, a stellar tidal disruption event was observed at a known black hole. Another team at Johns Hopkins University in Baltimore, Maryland, U.S., detected three additional events. In each case, astronomers hypothesized that the astrophysical jet created by the dying star would emit ultraviolet and X-ray radiation, which would be absorbed by the dust surrounding the black hole and emitted as infrared radiation. Not only was this infrared emission detected, but they concluded that the delay between the jet's emission of ultraviolet and X-ray radiation and the dust's emission of infrared radiation may be used to estimate the size of the black hole devouring the star. [12] [13]

In September 2019, scientists using the TESS satellite announced they had witnessed a tidal disruption event called ASASSN-19bt, 375 million light-years away. [14] [15]

In July 2020, astronomers reported the observation of a "hard tidal disruption event candidate" associated with ASASSN-20hx, located near the nucleus of galaxy NGC 6297, and noted that the observation represented one of the "very few tidal disruption events with hard powerlaw X-ray spectra". [16] [17]

The tidal-disruption radius ${\displaystyle R_{T}}$ is the distance at which a black hole of mass ${\displaystyle M_{BH}}$ would tidally disrupt an approaching star of radius ${\displaystyle R^{*}}$ and mass ${\displaystyle M^{*}}$, given approximately by:

${\displaystyle R_{T}\approx R^{*}({\frac {M_{BH}}{M^{*}}})^{\frac {1}{3}}}$

Usually the tidal-disruption radius of black hole is bigger than its Schwarzschild radius ${\displaystyle R_{S}={\frac {2GM}{c^{2}}}}$, but considering the radius and mass of the star fixed there is a mass for the black hole where both radius become equal ${\displaystyle R_{T}=R_{S}}$ meaning that at this point the star would simply disappear before being torn apart. [18] [19]

## Related Research Articles

A black hole is a region of spacetime where gravity is so strong that nothing – no particles or even electromagnetic radiation such as light – can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has a great effect on the fate and circumstances of an object crossing it, it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.

A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".

The Schwarzschild radius or the gravitational radius is a physical parameter in the Schwarzschild solution to Einstein's field equations that corresponds to the radius defining the event horizon of a Schwarzschild black hole. It is a characteristic radius associated with any quantity of mass. The Schwarzschild radius was named after the German astronomer Karl Schwarzschild, who calculated this exact solution for the theory of general relativity in 1916.

Messier 87 is a supergiant elliptical galaxy with several trillion stars in the constellation Virgo. One of the largest and most massive galaxies in the local universe, it has a large population of globular clusters — about 15,000 compared with the 150–200 orbiting the Milky Way — and a jet of energetic plasma that originates at the core and extends at least 1,500 parsecs, traveling at a relativistic speed. It is one of the brightest radio sources in the sky and a popular target for both amateur and professional astronomers.

A supermassive black hole is the largest type of black hole, with its mass being on the order of millions to billions of times the mass of the Sun (M). Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, not even light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its center. For example, the Milky Way has a supermassive black hole in its Galactic Center, corresponding to the radio source Sagittarius A*. Accretion of interstellar gas onto supermassive black holes is the process responsible for powering active galactic nuclei and quasars.

The Galactic Center is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact radio source which is almost exactly at the galactic rotational center. The Galactic Center is approximately 8 kiloparsecs (26,000 ly) away from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius, where the Milky Way appears brightest, visually close to the Butterfly Cluster (M6) or the star Shaula, south to the Pipe Nebula.

Sagittarius A*, abbreviated Sgr A* is the supermassive black hole at the Galactic Center of the Milky Way. It is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, visually close to the Butterfly Cluster (M6) and Lambda Scorpii.

The Sombrero Galaxy is a peculiar galaxy of unclear classification in the constellation borders of Virgo and Corvus, being about 9.55 megaparsecs from our galaxy. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It has a diameter of approximately 15 kiloparsecs, three-tenths the size of the Milky Way.

Messier 32 is a dwarf "early-type" galaxy about 2,650,000 light-years (810,000 pc) from the Solar System, appearing in the constellation Andromeda. M32 is a satellite galaxy of the Andromeda Galaxy (M31) and was discovered by Guillaume Le Gentil in 1749. Its true size is about 34 of the radius of the Sun from the local galactic centre, 6,300–6,700 light-years (1,900–2,100 pc) at its quite unpronounced widest.

Brandon Carter, is an Australian theoretical physicist, best known for his work on the properties of black holes and for being the first to name and employ the anthropic principle in its contemporary form. He is a researcher at the Meudon campus of the Laboratoire Univers et Théories, part of the CNRS.

NGC 4725 is an intermediate barred spiral galaxy with a prominent ring structure, located in the northern constellation of Coma Berenices near the north galactic pole. It was discovered by German-born astronomer William Herschel on April 6, 1785. The galaxy lies at a distance of approximately 40 megalight-years from the Milky Way.

Jean-Pierre Luminet is a French astrophysicist, specializing in black holes and cosmology. He is an emeritus research director at the CNRS. Luminet is a member of the Laboratoire d'Astrophysique de Marseille (LAM) and Laboratoire Univers et Théories (LUTH) of the Paris-Meudon Observatory, and is a visiting scientist at the Centre de Physique Théorique (CPT) in Marseilles. He is also a writer and poet.

The sphere of influence is a region around a supermassive black hole in which the gravitational potential of the black hole dominates the gravitational potential of the host galaxy. The radius of the sphere of influence is called the "(gravitational) influence radius".

S2, also known as S0–2, is a star in the star cluster close to the supermassive black hole Sagittarius A* (Sgr A*), orbiting it with a period of 16.0518 years, a semi-major axis of about 970 au, and a pericenter distance of 17 light hours – an orbit with a period only about 30% longer than that of Jupiter around the Sun, but coming no closer than about four times the distance of Neptune from the Sun. The mass when the star first formed is estimated by the European Southern Observatory (ESO) to have been approximately 14 M. Based on its spectral type, it probably has a mass of 10 to 15 solar masses.

A hypercompact stellar system (HCSS) is a dense cluster of stars around a supermassive black hole that has been ejected from the center of its host galaxy. Stars that are close to the black hole at the time of the ejection will remain bound to the black hole after it leaves the galaxy, forming the HCSS.

An intergalactic star, also known as an intracluster star or a rogue star, is a star not gravitationally bound to any galaxy. Although a source of much discussion in the scientific community during the late 1990s, intergalactic stars are now generally thought to have originated in galaxies, like other stars, before being expelled as the result of either galaxies colliding or of a multiple-star system traveling too close to a supermassive black hole, which are found at the center of many galaxies.

Swift J164449.3+573451, initially referred to as GRB 110328A, and sometimes abbreviated to Sw J1644+57, was a tidal disruption event, the destruction of a star by a supermassive black hole. It was first detected by the Swift Gamma-Ray Burst Mission on March 28, 2011. The event occurred in the center of a small galaxy in the Draco constellation, about 3.8 billion light-years away.

Bahcall–Wolf cusp refers to a particular distribution of stars around a massive black hole at the center of a galaxy or globular cluster. If the nucleus containing the black hole is sufficiently old, exchange of orbital energy between stars drives their distribution toward a characteristic form, such that the density of stars, ρ, varies with distance from the black hole, r, as

ASASSN-15lh is an extremely luminous astronomical transient event discovered by the All Sky Automated Survey for SuperNovae (ASAS-SN), with the appearance of a superluminous supernova event. It was first detected on June 14, 2015, located within a faint galaxy in the southern constellation Indus, and was the most luminous supernova-like object ever observed. At its peak, ASASSN-15lh was 570 billion times brighter than the Sun, and 20 times brighter than the combined light emitted by the Milky Way Galaxy. The emitted energy was exceeded by PS1-10adi.

ASASSN-19bt is a tidal disruption event, a star destroyed by a black hole, discovered by the All Sky Automated Survey for SuperNovae (ASAS-SN) project, with early-time, detailed observations by the TESS satellite. It was first detected on January 21st, 2019, and reached peak brightness on March 4th. The black hole is in the 16th magnitude galaxy 2MASX J07001137-6602251 in the constellation Volans at a redshift of 0.0262, around 375 million light years away.

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