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TON 618 (abbreviation of Tonantzintla 618) is a hyperluminous, broad-absorption-line, radio-loud quasar, and Lyman-alpha blob located near the border of the constellations Canes Venatici and Coma Berenices, with the projected comoving distance of approximately 18.2 billion light-years from Earth. It possesses one of the most massive black holes ever found, at 40.7 billion M_☉.

Observational history

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 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.

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

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 4×10 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. 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. From this, the mass of the central black hole of TON 618 has been estimated to be at 66 billion M_☉. 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 64 billion M_☉, 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. A black hole of this mass has a Schwarzschild radius of 1,300 AU (about 390 billion km or 0.04 ly in diameter) which is more than 40 times the distance from Neptune to the Sun, and its event horizon is large enough to fit over 30 solar systems inside of it.

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 2761±423 km/s, which indicate a lower mass for the central black hole at 40.7 billion M_☉, consequentially lower than the previous estimate.

Lyman-alpha nebula

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. 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.

In the case of TON 618, the enormous Lyman-alpha nebula surrounding it has the diameter of at least 100 kiloparsecs (330,000 light-years), 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 M_☉, 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. 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

Other notable objects in the Tonantzintla Catalogue

• 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.

Notes

1. This distance may seem to contradict the age of the Universe and is greater than the oldest light of the most distant objects. However, the time difference corresponds to another quantity, light-travel distance, which is only 10.8 billion light years. See Distance measures (cosmology) which explains the distance measures used in cosmology.

References

1. ^ "NED results for object TON 618". NASA/IPAC EXTRAGALACTIC DATABASE. Archived from the original on 2021-08-15. Retrieved 2021-08-15.
2. ^ Li, Jianrui; Emonts, B. H. C.; Cai, Z.; Prochaska, J. X.; Yoon, I.; Lehnert, M. D.; Zhang, S.; Wu, Y.; Li, Jianan; Li, Mingyu; Lacy, M.; Villar-Martín, M. (25 November 2021). "Massive Molecular Outflow and 100 kpc Extended Cold Halo Gas in the Enormous Lyα Nebula of QSO 1228+3128". The Astrophysical Journal Letters. 922 (2): L29. arXiv:2111.06409. Bibcode:2021ApJ...922L..29L. doi:10.3847/2041-8213/ac390d. S2CID 244102865.
3. ^ Ge, Xue; Bi-Xuan, Zhao; Wei-Hao, Bian; Green Richard, Frederick (21 March 2019). "The Blueshift of the C IV Broad Emission Line in QSOs". The Astronomical Journal. 157 (4): 14. arXiv:1903.08830. Bibcode:2019AJ....157..148G. doi:10.3847/1538-3881/ab0956. S2CID 84842636.
4. "1963: Maarten Schmidt Discovers Quasars". Observatories of the Carnegie Institution for Science. Archived from the original on 1 February 2019. Retrieved 21 October 2017.
5. Iriarte, Braulio; Chavira, Enrique (1957). "Estrellas Azules en el Casquete Galactico Norte (Blue stars in the North Galactic Cap)" (PDF). Boletín de los Observatorios de Tonantzintla y Tacubaya. 2 (16): 3–36. Archived (PDF) from the original on 22 October 2017. Retrieved 21 October 2017.
6. Colla, G.; Fanti, C.; Ficarra, A.; Formiggini, L.; Gandolfi, E.; Grueff, G.; Lari, C.; Padrielli, L.; Roffi, G.; Tomasi, P; Vigotti, M. (1970). "A catalogue of 3235 radio sources at 408 MHz". Astronomy & Astrophysics Supplement Series. 1 (3): 281. Bibcode:1970A&AS....1..281C.
7. ^ Ulrich, Marie-Helene (1976). "Optical spectrum and redshifts of a quasar of extremely high intrinsice luminosity: B2 1225+31". The Astrophysical Journal. 207: L73 – L74. Bibcode:1976ApJ...207L..73U. doi:10.1086/182182.
8. Kaspi, Shai; Smith, Paul S.; Netzer, Hagai; Maos, Dan; Jannuzi, Buell T.; Giveon, Uriel (2000). "Reverberation measurements for 17 quasars and the size-mass-luminosity relations in active galactic nuclei". The Astrophysical Journal. 533 (2): 631–649. arXiv:astro-ph/9911476. Bibcode:2000ApJ...533..631K. doi:10.1086/308704. S2CID 119022275.
9. ^ Shemmer, O.; Netzer, H.; Maiolino, R.; Oliva, E.; Croom, S.; Corbett, E.; di Fabrizio, L. (2004). "Near-infrared spectroscopy of high-redshift active galactic nuclei: I. A metallicity-accretion rate relationship". The Astrophysical Journal. 614 (2): 547–557. arXiv:astro-ph/0406559. Bibcode:2004ApJ...614..547S. doi:10.1086/423607. S2CID 119010341.
10. McMillan, P. J. (July 2011). "Mass models of the Milky Way". Monthly Notices of the Royal Astronomical Society. 414 (3): 2446–2457. arXiv:1102.4340. Bibcode:2011MNRAS.414.2446M. doi:10.1111/j.1365-2966.2011.18564.x. S2CID 119100616.
11. Irving, Michael (21 February 2018). ""Ultramassive" black holes may be the biggest ever found – and they're growing fast". New Atlas. Archived from the original on 31 March 2019. Retrieved 21 August 2018.
12. "From Super to Ultra: Just How Big Can Black Holes Get?". NASA – Chandra X-Ray Observatory. 18 December 2012. Archived from the original on 17 June 2019. Retrieved 21 August 2018.
13. Sargent, W. L. W.; Young, P. J.; Boksenberg, A.; Tytler, D. (1980). "The distribution of Lyman-alpha absorption lines in the spectra of six QSOs: evidence for an intergalactic origin". The Astrophysical Journal Supplement Series. 42: 41. Bibcode:1980ApJS...42...41S. doi:10.1086/190644.
14. Khare, P.; Srianand, R.; York, D. G.; Green, R.; Welty, D.; Huang, K.-L.; Bechtold, J. (1997). "The Lyman alpha forest towards B2 1225 + 317". Monthly Notices of the Royal Astronomical Society. 285 (1): 167–180. arXiv:astro-ph/9612163. doi:10.1093/mnras/285.1.167. Archived from the original on 2022-01-29. Retrieved 2022-01-29.
15. Steidel, C. C.; Adelberger, K. L.; Shapley, A. E. (2000). "Lyα Imaging of a Proto–Cluster Region at ⟨ z ⟩ = 3.09". Astrophysical Journal. 532 (1): 170–82. arXiv:astro-ph/9910144. Bibcode:2000ApJ...532..170S. doi:10.1086/308568. S2CID 10353723.
16. "Giant Space Blob Glows from Within". ESO Press Release. 17 August 2011. Archived from the original on 28 September 2011. Retrieved 18 August 2011.

External links

• NASA animation illustrating the relative sizes of black holes including TON 618

v t e Constellation of Canes Venatici
Canes Venatici in Chinese astronomy Giant Void List of stars in Canes Venatici
Stars	Bayer α α (Cor Caroli) β (Chara) Flamsteed 4 5 6 10 19 20 21 24 25 Variable R Y (La Superba) RS AM AW BH DG HR 4997 Other Gliese 521 HAT-P-12 HAT-P-36 (Tuiren) CWISE J1249+3621
Exoplanets HAT-P-12b
Star clusters Messier 3
Galaxies	Messier 51 a (Whirlpool Galaxy) b 63 94 106 NGC 4111 4138 4145 4151 4163 4183 4214 4217 4242 4244 4395 4399 4400 4401 4449 4485 4490 4534 4618 4625 4627 4631 4656 4657 4707 4800 4861 5002 5003 5005 5023 5033 5112 5223 5229 5238 5273 5371 5394 Numbered I II Other 3C 285 3C 286 3C 288 DDO 169 IC 883 IC 4182 IC 4263 IC 4271 I Zwicky 36 KKR 03 4C +41.26 TON 618
Galaxy clusters Canes II Group M51 Group M94 Group NGC 4631 Group
Astronomical events GRB 090429B SN 1994I SN 2005cs SN 2008ax
Category

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• Quasars
• Astronomical objects discovered in 1957
• Canes Venatici
• Supermassive black holes
• Lyman-alpha blobs