TON 618

As quasars were not recognized until 1963,{{cite web|title=1963: Maarten Schmidt Discovers Quasars|url=https://cosmology.carnegiescience.edu/timeline/1963|publisher=Observatories of the Carnegie Institution for Science|access-date=21 October 2017|archive-date=1 February 2019|archive-url=https://web.archive.org/web/20190201113138/http://cosmology.carnegiescience.edu/timeline/1963|url-status=dead}} 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 0.7 m Schmidt telescope at the Tonantzintla Observatory in Mexico, it appeared "decidedly violet" and was listed by the Mexican astronomers Braulio Iriarte and Enrique Chavira as entry number 618 in the Tonantzintla Catalogue.{{cite journal | last1=Iriarte | first1=Braulio | last2=Chavira | first2=Enrique | title=Estrellas Azules en el Casquete Galactico Norte (Blue stars in the North Galactic Cap) | journal=Boletín de los Observatorios de Tonantzintla y Tacubaya | date=1957 | volume=2 | issue=16 | pages=3–36 | url=http://www.astroscu.unam.mx/bott/BOTT..2-16/PDF/BOTT..2-16_biriarte.pdf | access-date=21 October 2017 | archive-date=22 October 2017 | archive-url=https://web.archive.org/web/20171022085150/http://www.astroscu.unam.mx/bott/BOTT..2-16/PDF/BOTT..2-16_biriarte.pdf | url-status=live }}

In 1970, a radio survey at Bologna in Italy discovered radio emissions from TON 618, indicating that it was a quasar.{{cite journal|last1=Colla|first1=G.|last2=Fanti|first2=C.|last3=Ficarra|first3=A.|last4=Formiggini|first4=L.|last5=Gandolfi|first5=E.|last6=Grueff|first6=G.|last7=Lari|first7=C.|last8=Padrielli|first8=L.|last9=Roffi|first9=G.|last10=Tomasi|first10=P|last11=Vigotti|first11=M.|title=A catalogue of 3235 radio sources at 408 MHz|journal=Astronomy & Astrophysics Supplement Series|date=1970|volume=1|issue=3|page=281|bibcode=1970A&AS....1..281C}} 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.{{cite journal|last1=Ulrich|first1=Marie-Helene|title=Optical spectrum and redshifts of a quasar of extremely high intrinsice luminosity: B2 1225+31|journal=The Astrophysical Journal|date=1976|volume=207|pages=L73–L74|doi=10.1086/182182|bibcode=1976ApJ...207L..73U|doi-access=free}}

File:Phoenix A compared to Ton 618 and the Orbit of Neptune.jpg. 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. 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 −30.7, it shines with a luminosity of {{val|4|e=40}} watts, or as brilliantly as 140 trillion times that of the Sun, making it one of the brightest objects in the known Universe.

Like other quasars, TON 618 has a spectrum containing emission lines from cooler gas much further out than the accretion disc, in the broad-line region. The size of the broad-line region can be calculated from the brightness of the quasar radiation that is lighting it up.{{cite journal|last1=Kaspi|first1=Shai|last2=Smith|first2=Paul S.|last3=Netzer|first3=Hagai|last4=Maos|first4=Dan|last5=Jannuzi|first5=Buell T.|last6=Giveon|first6=Uriel|title=Reverberation measurements for 17 quasars and the size-mass-luminosity relations in active galactic nuclei|journal=The Astrophysical Journal|date=2000|volume=533|issue=2|pages=631–649|arxiv=astro-ph/9911476|bibcode=2000ApJ...533..631K|doi=10.1086/308704|s2cid=119022275}} Shemmer and coauthors used both N_V and C_IV emission lines in order to calculate the widths of the H_β 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.

The emission lines in the spectrum of TON 618 have been found to be unusually wide, indicating that the gas is travelling very fast; the full width half maxima of TON 618 has been the largest of the 29 quasars, with hints of 10,500 km/s speeds of infalling material by a direct measure of the H_β spectral line, indication of a very strong gravitational force.{{cite journal|last1=Shemmer|first1=O.|last2=Netzer|first2=H.|last3=Maiolino|first3=R.|last4=Oliva|first4=E.|last5=Croom|first5=S.|last6=Corbett|first6=E.|last7=di Fabrizio|first7=L.|title=Near-infrared spectroscopy of high-redshift active galactic nuclei: I. A metallicity-accretion rate relationship|journal=The Astrophysical Journal|date=2004|volume=614|issue=2|pages=547–557|arxiv=astro-ph/0406559|bibcode=2004ApJ...614..547S|doi=10.1086/423607|s2cid=119010341}} From this, the mass of the central black hole of TON 618 has been estimated to be at {{solar mass|66 billion}}. This is considered one of the highest masses ever recorded for such an object; higher than the mass of all the stars in the Milky Way galaxy combined, which is {{solar mass|64 billion}},{{Cite journal |last1=McMillan |first1=P. J. |title=Mass models of the Milky Way |doi=10.1111/j.1365-2966.2011.18564.x |journal=Monthly Notices of the Royal Astronomical Society |volume=414 |issue=3 |pages=2446–2457 |date=July 2011 |doi-access=free |bibcode=2011MNRAS.414.2446M |arxiv=1102.4340|s2cid=119100616 }} and 15,300 times more massive than Sagittarius A*, the Milky Way's central black hole. With such high mass, TON 618 may fall into a proposed new classification of ultramassive black holes.{{cite web |url=https://newatlas.com/ultramassive-black-holes/53493/ |title="Ultramassive" black holes may be the biggest ever found – and they're growing fast |website=New Atlas |first=Michael |last=Irving |date=21 February 2018 |access-date=21 August 2018 |archive-date=31 March 2019 |archive-url=https://web.archive.org/web/20190331231814/https://newatlas.com/ultramassive-black-holes/53493/ |url-status=live }}{{cite web |url=https://www.nasa.gov/mission_pages/chandra/news/ultra_black_holes.html |title=From Super to Ultra: Just How Big Can Black Holes Get? |publisher=NASA – Chandra X-Ray Observatory |date=18 December 2012 |access-date=21 August 2018 |archive-date=17 June 2019 |archive-url=https://web.archive.org/web/20190617101304/https://www.nasa.gov/mission_pages/chandra/news/ultra_black_holes.html |url-status=live }} A black hole of this mass has a Schwarzschild radius of 1,300 AU (about 195 billion km or 0.02 ly) which is more than 40 times the distance from Neptune to the Sun.

A more recent measurement in 2019 by Ge and colleagues which utilizes the C IV emission line, an alternative spectral line to H_β, using the same data reproduced by the earlier paper by Shemmer found a lower relative velocity of the surrounding gas of {{val|2,761|423|ul=km/s|fmt=commas}}, which indicate a lower mass for the central black hole at {{solar mass|40.7 billion|link=y}}, consequentially lower than the previous estimate.{{cite journal|last1=Ge|first1=Xue|last2=Bi-Xuan|first2=Zhao|last3=Wei-Hao|first3= Bian|last4=Green Richard|first4=Frederick|title=The Blueshift of the C IV Broad Emission Line in QSOs|journal=The Astronomical Journal|date=21 March 2019|volume=157|issue=4|pages=14|arxiv=1903.08830|bibcode=2019AJ....157..148G|doi=10.3847/1538-3881/ab0956|s2cid=84842636 |doi-access=free }}

{{see also|Lyman-alpha blob}}

Image:Computer simulation of a Lyman-alpha Blob.jpg. 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.{{cite journal|title=The distribution of Lyman-alpha absorption lines in the spectra of six QSOs: evidence for an intergalactic origin.|bibcode=1980ApJS...42...41S|last1=Sargent|first1=W. L. W.|last2=Young|first2=P. J.|last3=Boksenberg|first3=A.|last4=Tytler|first4=D.|journal=The Astrophysical Journal Supplement Series|year=1980|volume=42|page=41|doi=10.1086/190644|doi-access=free}} 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.{{cite journal|title = The Lyman alpha forest towards B2 1225 + 317|year = 1997|doi = 10.1093/mnras/285.1.167|url = https://academic.oup.com/mnras/article/285/1/167/993418?login=false|last1 = Khare|first1 = P.|last2 = Srianand|first2 = R.|last3 = York|first3 = D. G.|last4 = Green|first4 = R.|last5 = Welty|first5 = D.|last6 = Huang|first6 = K.-L.|last7 = Bechtold|first7 = J.|journal = Monthly Notices of the Royal Astronomical Society|volume = 285| issue=1 |pages = 167–180|doi-access = free|access-date = 2022-01-29|archive-date = 2022-01-29|archive-url = https://web.archive.org/web/20220129184513/https://academic.oup.com/mnras/article/285/1/167/993418?login=false|url-status = live|arxiv = astro-ph/9612163}}

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. This would make it a Lyman-alpha blob (LAB), one of the largest such objects yet known.

LABs are huge collections of gases, or nebulae, that are also classified as Lyman-alpha emitters. These enormous, galaxy-sized clouds are some of the largest nebulae known to exist, with some identified LABs in the 2000s reaching sizes of at least hundreds of thousands of light-years across.{{cite journal|title= Lyα Imaging of a Proto–Cluster Region at ⟨ z ⟩ = 3.09 |last1=Steidel |first1=C. C. |last2=Adelberger |first2=K. L. |last3=Shapley |first3=A. E.|year= 2000 |journal= Astrophysical Journal |volume= 532 |issue = 1|pages= 170–82|arxiv = astro-ph/9910144 |bibcode = 2000ApJ...532..170S |doi = 10.1086/308568 |s2cid=10353723 }}

In the case of TON 618, the enormous Lyman-alpha nebula surrounding it has the diameter of at least {{convert|100|kpc|ly|abbr=off}}, twice the size of the Milky Way. The nebula consists of two parts: an inner molecular outflow and an extensive cold molecular gas in its circumgalactic medium, each having the mass of 50 billion {{solar mass}}, with both of them being aligned to the radio jet produced by the central quasar. The extreme radiation from TON 618 excites the hydrogen in the nebula so much that it causes it to glow brightly in the Lyman-alpha line, consistent with the observations of other LABs driven by their inner galaxies.{{cite news|title=Giant Space Blob Glows from Within|url=http://www.eso.org/public/news/eso1130/|access-date=18 August 2011|newspaper=ESO Press Release|date=17 August 2011|archive-date=28 September 2011|archive-url=https://web.archive.org/web/20110928033049/http://www.eso.org/public/news/eso1130/|url-status=live}} 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.

• NGC 6380 – globular cluster listed as TON 1, the first entry of the Tonantzintla Catalogue.
• SX Leonis Minoris – variable star listed as TON 45.
• U Geminorum – star system listed as TON 842.
• RZ Leonis Minoris – cataclysmic variable listed as TON 1107.

{{notelist}}

{{reflist}}

• [https://www.nasa.gov/feature/goddard/2023/nasa-animation-sizes-up-the-universe-s-biggest-black-holes NASA animation illustrating the relative sizes of black holes including TON 618]

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