TON 618

As quasars were not recognized until 1963, the nature of this object was unknown when it was first noted in a 1957 survey of faint blue stars (mainly white dwarfs) that lie away from the plane of the Milky Way. On photographic plates taken with the Schmidt telescope at the Tonantzintla Observatory in Mexico, it appeared as "decidedly violet" or faint blue star and was listed by the Mexican astronomers Braulio Iriarte and Enrique Chavira as entry number 618 in the Tonantzintla Catalogue. Thirteen years later, in 1970, a radio survey at Bologna in Italy discovered radio emissions from TON 618, indicating that it was a quasar. Marie-Helene Ulrich then obtained optical spectra of TON-618 at the McDonald Observatory which showed emission lines typical of a quasar. From the high redshift of the lines, Ulrich deduced that TON-618 was very distant, and hence was one of the most luminous quasars known. == Components ==

Supermassive black hole . The orbit of Neptune (white oval) is included for comparison. As a quasar, TON 618 is believed to be the active galactic nucleus at the center of a galaxy, the engine of which is a supermassive black hole feeding on intensely hot gas and matter in an accretion disc. Given its observed redshift of 2.219, the light travel time of TON-618 is estimated to be approximately 10.8 billion years, which is directly proportional to its distance in light years. Due to the brilliance of the central quasar, the surrounding galaxy is outshone by it and hence is not visible from Earth. With an absolute magnitude of , it shines with a luminosity of , or as brilliantly as 140 trillion times that of the Sun, making it one of the brightest objects in the known universe. Shemmer and coauthors used both N and C emission lines in order to calculate the widths of the H spectral line of at least 29 quasars, including TON-618, as a direct measurement of their accretion rates and hence the mass of the central black hole. From this, the mass of the central black hole of TON-618 has been estimated to be at . and 15,300 times more massive than Sagittarius A*, the Milky Way's central black hole at a relatively modest and extends 17☉. With such high mass, TON 618 may fall to the summit a proposed new classification of Ultramassive black holes. A black hole of this mass has a Schwarzschild radius of which is more than 60 times the distance from Pluto to the Sun. In other words, 283,000 solar radii. A more recent measurement in 2019 by Xue Ge et al. which utilizes the C IV emission line, an alternative spectral line to H—using the same data reproduced by the earlier paper by Shemmer—found a lower relative velocity of the surrounding gas of , which indicates a lower mass for the central black hole at , consequentially lower than the previous estimate. Due to the Schwarzchild radius growing proportionately to a black hole's mass, this would correspond to an event horizon spanning , about 40 times the distance from Pluto to the Sun. Evolution models based on the revisited mass of TON 618's (super/ultra)massive black hole predict that it will live for roughly years (near the end of the Black Hole Era of the universe, when it is more than 1088 times its current age), before it dissipates via Hawking radiation. Hawking radiation, to put it simply, is the process by which black holes lose a negligible amount of mass at any given moment. When mass enters the black hole, a trace amount of the black hole's mass is emitted, taking a minuscule amount of the black hole's energy with it. Over unfathomably long time-spans( for stellar mass black holes and for the largest possible ones), the black hole will likely lose more mass at an exponential rate, before finally evaporating and potentially ending in a dramatic explosion. Now, whether or not that explosion occurs is primarily a matter of speculation. Lyman-alpha nebula . A similar gas cloud is present at TON-618. The nature of TON-618 as a Lyman-alpha emitter has been well documented since at least the 1980s. Lyman-alpha emitters are characterized by their significant emission of the Lyman-alpha line, an ultraviolet wavelength emitted by neutral hydrogen. Such objects, however, have been very difficult to study due to the Lyman-alpha line being strongly absorbed by air in the Earth's atmosphere, limiting study of Lyman-alpha emitters to those objects with high redshifts. TON-618, with its luminous emission of Lyman-alpha radiation along with its high redshift, has made it one of the most important objects in the study of the Lyman-alpha forest. Observations made by the Atacama Large Millimeter Array (ALMA) in 2021 revealed the apparent source of the Lyman-alpha radiation of TON 618: an enormous cloud of gas surrounding the quasar and its host galaxy. In the case of TON-618, the enormous Lyman-alpha nebula surrounding it has the diameter of at least , triple the size of the Milky Way. Since both quasars and LABs are precursors of modern-day galaxies, the observation on TON 618 and its enormous LAB gave insight to the processes that drive the evolution of massive galaxies, in particular probing their ionization and early development. ==See also==