A tidal disruption event is an astronomical phenomenon that occurs when a star approaches sufficiently close to a supermassive black hole that it is pulled apart by the black hole's tidal force, experiencing spaghettification. 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.
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". Wheeler succeeded in applying the relativistic generalization of the classical Newtonian tidal disruption problem to the neighborhood 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. 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 and in 1983 in Astronomy & Astrophysics. The authors had managed to describe the tidal disturbances in the heart of 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". 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. 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 but also in the heart of the Milky Way. The TDE theory even explains the superluminous supernovaSN 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" 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 NASAWide-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 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. In September 2019, scientists using the TESS satellite announced they had witnessed a tidal disruption event of the star ASASSN-19bt, 375 million light years away. 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".
