I Zwicky 1

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I Zwicky 1
A picture of I ZW 1 taken by HST.jpg
Hubble Space Telescope image of I Zwicky 1
Observation data (J2000 epoch)
Constellation Pisces
Right ascension 00h 53m 34.94s
Declination +12d 41m 36.20s
Redshift 0.061169
Heliocentric radial velocity 18,338 km/s
Distance 847 Mly (259.7 Mpc)
Apparent magnitude  (V)0.43
Apparent magnitude  (B)0.54
Surface brightness 14.4
Characteristics
Type Sa;Sy1, Sbrst
Size0.5' x 0.5'
Notable features Seyfert galaxy containing a quasar
Other designations
UGC 545, PG 0050+124, PGC 3151, IRAS 00509+1225, RBS 0129, 2E 209, PHL 3072, Mrk 1502, Mrk 9009, NVSS J005334+124133

I Zwicky 1 (shortened to I Zw 1), also known as UGC 545, is a galaxy located in the constellation Pisces. It is located 847 million light-years from Earth [1] and is said to be the nearest quasar (QSO) due to its high optical nuclear luminosity of MV = -23.8 mag. [2]

Contents

Discovery

I Zwicky 1 was discovered by Fritz Zwicky in 1964. According to Zwicky, the object is classified as a compact galaxy, whom he commented it as "variable blue spherical, very compact, with a patchy halo. It is listed as the first object in the Zwicky catalogue. [3] At the redshift of 0.0611, [4] I Zwicky 1 shows spectral properties of high-redshift quasars that are blueshifted by 1350 km-1 according to the study conducted by Buson & Ulrich in 1990. [5]

The photometric history of I Zwicky 1, dates back to 1909, where it has been investigated on Harvard photographic plates. The available data indicates the galaxy is variable and probably undergoes outbursts of about 0.7 mag above a brightness level that is itself variable by about 0.7 mag. [6]

Characteristics

Sloan Digital Sky Survey of I Zwicky 1 SDSS image of I Zw 1.png
Sloan Digital Sky Survey of I Zwicky 1

The nucleus of I Zwicky 1 is found to be active. It is classified as a prototypical narrow-line Seyfert 1 galaxy [7] [8] [9] and contains high amounts of X-ray luminosity. [10] [11] The galaxy contains a peculiar spectrum, which in addition to the usual broad and narrow line regions, there are two emission regions emitting broad and blue shifted [O III] lines making it a peculiarly interesting object. [12] The QSO sits inside its host galaxy which is revealed to be a face-on spiral galaxy. It shows two asymmetric spiral arms and knots of star formation. [3] This makes I Zwicky 1 an ideal candidate for studying properties of QSO hosts. [2] It is also possible that certain tidal interactions triggers activity in I Zwicky 1, both starburst and QSO. [13]

I Zwicky 1 is classified a Markarian galaxy (designated both Mrk 1502 and Mrk 9009). Compared to other galaxies, the nucleus emits excessive amounts of ultraviolet rays. [14] This is caused by undergoing a strong starburst located in the central ring-like area of the galaxy. [3]

Further study on I Zwicky 1

I Zwicky 1 shows existence of V-, R-, and H-bands [15] [16] with sturdy carbon monoxide (CO) featured in the J = 1-0 and J = 2-1 lines. When further observed, researchers found that the J = 1-0 line is brighter compared to the J = 2-1 line found with less luminosity. Given location in galactic molecular clouds, the carbon monoxide must be larger on the scale of the 26 kpc J = 1-0 beam size, with optical depth and being thermalized. [17]

Researchers who studied interstellar medium and star formation, found out a two-component model is required for I Zwicky 1 in which 2/3 of the far-infrared brightness originates in the disk and 1/3 originates from the nucleus. The star-forming rate, efficiency of the disk and the nucleus of I Zwicky 1 was estimated by researchers, whom they found that the values are similar to the luminosity of galaxies studied by IRAS. Overall, the disc star-formation, is closer to topmost values of ~30 L_sun_/M_sun_ that is found inside galactic star-forming regions of the Milky Way such as M17 or W51. When looking at its nuclear near-infrared colors analysis, researchers suggest I Zwicky 1 has a combined quasar nucleus and defunct stellar component that matches about 10%-20% of the flux density at 2.2 microns. [18] This suggests the size of I Zwicky 1's molecular bulge is estimated to be 1" to 2" (1.2-2.4 kpc). But only the nucleus is revealed through optical spectrum and large X-ray luminosity. [18]

Millimeter Spectroscopy

Further studies showed the mapping of 12CO (10) line emission in I Zwicky 1 whom researchers conducted observations with Institut de Radio Astronomie Millimetrique (IRAM) millimeter interferometer on the Plateau de Bure, France, between January and February 1995. [19] There, they placed four 15 m antennas in four different configurations. With 24 baselines provided by the four 15 m antennas, ranging from 24 to 288 m in length, they were supplied by SIS receivers with single-sideband (SSB) system temperatures of 170 K above the atmosphere. Located at redshift 0.0611, the observed frequency of I Zwicky 1 was 108.633 GHz.

The CO maps were seen by the observations from IRAM 30m telescope. This resolution of a synthesized beam was uniform weighted of 19, but 5 resolution CLEAN maps (natural weighting) were made by spectral resolutions of 10 km s−1 and 40 km s−1 to examine the extended disk structure and velocity field. For the core component, researchers used the 19 resolution CLEANed maps with a spectral resolution of 20 km s−1. To investigate the structure dynamics of the nucleus, which they reckoned these velocity maps together with p-v diagrams alongside major and minor kinematic axes of I Zwicky 1. [2]

Near-Infrared Spectroscopy and Imaging

I Zwicky 1 was observed by K-band (2.20 m) in January, 1995 with a MPE imaging spectrometer making use of 3D images [20] with a 3.6 m telescope in Calar Alto, Spain. The observations in the H-band (1.65 m) on the other hand, were carried out in December 1995, at the William Herschel Telescope located in La Palma, Canary Islands. From two observations, researchers found that the image scale was 05 pixel−1 and total integration time on source was 4200 s and 1530 s for the K-band and H-band respectively. [2]

Molecular gas properties

The properties of the molecular gas are important for acknowledging the total star formation and powering AGNs, given molecular clouds are the major reservoirs for such occurrences. According to researchers, looking inside the spiral arms of the QSO host galaxy, they detected the molecular line emission. Seeing this, they were able to break up the line emission into a separate core and disk components. Through analyzing the velocity field, a circumnuclear ring of molecular gas is found. It has a similar size to starburst rings in nearby galaxies. With a spatial resolution of 19 (2.2 kpc), no signs of gas is suggested streaming straight to the nucleus. [2]

Comparison of starburst rings

In a study where starburst rings are observed in galaxies, [21] the rings in I Zwicky 1 are suggested to be formed by gravitational interactions, because of high rates of stars and gas. These rings are detected in midinfrared continuum, near-infrared colors, molecular gas line emission, and H line emission. Although, the overall structure of these rings aren't even, it is feasible they are formed by two twisted spiral arms on every side of the nucleus. [2] To see whether the rings are unique or ordinary, researchers found two other galaxies, NGC 7552 and NGC 7469. They found the ring properties are alike to one another for all three galaxies. But there is a difference in total bolometric luminosity which might be linked to the internal structure of the rings, and to a certain, starburst regions are fueled within the ring region. [2]

The starburst rings of I Zwicky 1 are 3 times older compared to those in NGC 7552 and NGC 7469. Using the comparison, the molecular ring researchers detected in the 12CO(10) line emission, might contain starburst like other circumnuclear rings. This indicates the luminosity fraction observed for QSOs and Seyfert galaxies is mainly caused by circumnuclear starbursts in the centers of host galaxies, and that the AGNs aren't only responsible for energy output overall in the optical and infrared light. [2] Such star formation activity contributed to bolometric luminosity only range about 10% to 50% in I Zwicky 1, compared to observations for NGC 7469. [22]

To sum things up, a young starburst is associated with this circumnuclear ring. The properties of this starburst ring in I Zwicky 1, are similar to nuclear activity sources. When looking at similarities, the rings are a possible common phenomenon that contributes significant fraction to luminosity in central regions. [2]

Supermassive black hole

The supermassive black hole in I Zwicky 1, has an estimated mass of M. = 9.30+1.26- 1.38 x 106 solar masses. This suggests the accretion rate is 203.9+61.0-65.8 L edd c-2, indicating there is a super-Eddington accretor, where LEdd is the Eddington luminosity and c is the speed of light. By splitting up Hubble Space Telescope images, researchers find the stellar mass of the bulge of its host galaxy is similar to log(M budge/M○ = 10.92 + 0.07. Looking at these values, they suggest the black hole has bulge mass ratio of ~10−4, which is smaller when compared to classical bulges of elliptical galaxies. [23]

An article published in 2021, found out according to observations by ESA's XMM-Newton and NASA's NuSTAR space telescopes, the black hole emits out X-ray flares from the region. Further analysis by researches showed, brief flashes of photons that are found consistent in the re-emergence of emission, proving they had reverberated from black hole's accretion disk in form light echoes, which are subsequently distorted and extended by the galaxy's strong gravitational field. [24] [25]

Related Research Articles

An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such excess, non-stellar emissions have been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an active galaxy. The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.

<span class="mw-page-title-main">Seyfert galaxy</span> Class of active galaxies with very bright nuclei

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasar host galaxies. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.

<span class="mw-page-title-main">NGC 5548</span> Type I Seyfert galaxy in the constellation Boötes

NGC 5548 is a Type I Seyfert galaxy with a bright, active nucleus. This activity is caused by matter flowing onto a 65 million solar mass (M☉) supermassive black hole at the core. Morphologically, this is an unbarred lenticular galaxy with tightly-wound spiral arms, while shell and tidal tail features suggest that it has undergone a cosmologically-recent merger or interaction event. NGC 5548 is approximately 245 million light years away and appears in the constellation Boötes. The apparent visual magnitude of NGC 5548 is approximately 13.3 in the V band.

<span class="mw-page-title-main">NGC 4194</span> Interacting galaxy pair in the constellation of Ursa Major

NGC 4194, the Medusa merger, is a galaxy merger in the constellation Ursa Major about 128 million light-years (39.1 Mpc) away. It was discovered on April 2, 1791 by German-British astronomer William Herschel. Due to its disturbed appearance, it is object 160 in Halton Arp's 1966 Atlas of Peculiar Galaxies.

<span class="mw-page-title-main">NGC 4536</span> Spiral galaxy in the constellation Virgo

NGC 4536 is an intermediate spiral galaxy in the constellation Virgo. It was discovered by German-British astronomer William Herschel on 24 January 1784.

<span class="mw-page-title-main">NGC 1614</span> Galaxy in the constellation Eridanus

NGC 1614 is the New General Catalogue identifier for a spiral galaxy in the equatorial constellation of Eridanus. It was discovered on December 29, 1885 by American astronomer Lewis Swift, who described it in a shorthand notation as: pretty faint, small, round, a little brighter middle. The nebula was then catalogued by Danish-Irish astronomer J. L. E. Drayer in 1888. When direct photography became available, it was noted that this galaxy displayed some conspicuous peculiarities. American astronomer Halton Arp included it in his 1966 Atlas of Peculiar Galaxies. In 1971, Swiss astronomer Fritz Zwicky described it as a "blue post-eruptive galaxy, compact patchy core, spiral plumes, long blue jet SSW".

<span class="mw-page-title-main">NGC 7552</span> Galaxy in the constellation Grus

NGC 7552 is a barred spiral galaxy in the constellation Grus. It is at a distance of roughly 60 million light years from Earth, which, given its apparent dimensions, means that NGC 7552 is about 75,000 light years across. It forms with three other spiral galaxies the Grus Quartet.

<span class="mw-page-title-main">NGC 2681</span> Galaxy in the constellation Ursa Major

NGC 2681 is a lenticular galaxy in the constellation Ursa Major. The galaxy lies 50 million light years away from Earth, which means, given its apparent dimensions, that NGC 2681 is approximately 55,000 light years across. NGC 2681 has an active galactic nucleus and it is a type 3 Seyfert galaxy. Its nucleus is also a low-ionization nuclear emission-line region.

<span class="mw-page-title-main">NGC 7469</span> Galaxy located in the constellation Pegasus

NGC 7469 is an intermediate spiral galaxy in the constellation of Pegasus. NGC 7469 is located about 200 million light-years away from Earth, which means, given its apparent dimensions, that NGC 7469 is approximately 90,000 light-years across. It was discovered by William Herschel on November 12, 1784.

<span class="mw-page-title-main">NGC 7130</span> Galaxy in the constellation Piscis Austrinus

NGC 7130 is a spiral galaxy located in the constellation Piscis Austrinus. It is located at a distance of about 220 million light years from Earth, which, given its apparent dimensions, means that NGC 7130 is about 100,000 light years across. It was discovered by John Herschel on September 25, 1834, and discovered independently by Lewis Swift on September 17, 1897. The location of the galaxy given in the New General Catalogue was off by 30 arcminutes in declination from the location of the galaxy.

<span class="mw-page-title-main">NGC 985</span> Ring galaxy in the constellation Cetus

NGC 985 is a ring galaxy in the constellation of Cetus. It is located about 550 million light years away from Earth, which means, given its apparent dimensions, that NGC 985 is approximately 160,000 light years across. It was discovered by Francis Leavenworth in 1886. It is a type 1 Seyfert galaxy.

<span class="mw-page-title-main">NGC 1386</span> Galaxy in the constellation Eridanus

NGC 1386 is a spiral galaxy located in the constellation Eridanus. It is located at a distance of circa 53 million light years from Earth, which, given its apparent dimensions, means that NGC 1386 is about 50,000 light years across. It is a Seyfert galaxy, the only one in Fornax Cluster.

<span class="mw-page-title-main">NGC 2273</span> Galaxy in the constellation Lynx

NGC 2273 is a barred spiral galaxy located in the constellation Lynx. It is located at a distance of circa 95 million light years from Earth, which, given its apparent dimensions, means that NGC 2273 is about 100,000 light years across. It was discovered by Nils Dunér on September 15, 1867.

<span class="mw-page-title-main">NGC 7679</span> Galaxy in the constellation Pisces

NGC 7679 is a lenticular galaxy with a peculiar morphology in the constellation Pisces. It is located at a distance of about 200 million light years from Earth, which, given its apparent dimensions, means that NGC 7679 is about 60,000 light years across. It was discovered by Heinrich d'Arrest on September 23, 1864. The total infrared luminosity is 1011.05 L☉, and thus it is categorised as a luminous infrared galaxy. NGC 7679 is both a starburst galaxy and a Seyfert galaxy.

<span class="mw-page-title-main">III Zw 2</span> Seyfert galaxy in the constellation Pisces

III Zw 2 is a Seyfert 1 galaxy located in the Pisces constellation. It has a redshift of 0.089 and is notable as the first of its kind to exhibit a superluminal jet.

<span class="mw-page-title-main">NGC 4324</span> Galaxy in the constellation of Virgo

NGC 4324 is a lenticular galaxy located about 85 million light-years away in the constellation Virgo. It was discovered by astronomer Heinrich d'Arrest on March 4, 1862. NGC 4324 has a stellar mass of 5.62 × 1010M☉, and a baryonic mass of 5.88 × 1010M☉. The galaxy's total mass is around 5.25 × 1011M☉. NGC 4324 is notable for having a ring of star formation surrounding its nucleus. It was considered a member of the Virgo II Groups until 1999, when its distance was recalculated and it was placed in the Virgo W Group.

<span class="mw-page-title-main">IRAS F11119+3257</span> Galaxy in the constellation Ursa Major

IRAS F11119+3257 or simply as F11119+3257, is a galaxy located in constellation Ursa Major. With a redshift of 0.187580, it has a light travel time distance of 2.5 billion light-years and is considered an ultraluminous infrared galaxy (ULIRG).

<span class="mw-page-title-main">PG 0844+349</span> Galaxy in the constellation Lynx

PG 0844+349, also known as TON 951, is a galaxy in the southern constellation Lynx, near the border of Cancer. Its redshift is 0.064000, putting the galaxy at 849 million light-years away from Earth.

<span class="mw-page-title-main">Markarian 463</span> Galaxy in the constellation of Boötes

Markarian 463 known as UGC 8850, is a galaxy merger located in the constellation Boötes. It is located 706 million light years from Earth. It is classified a double nucleus Seyfert galaxy.

<span class="mw-page-title-main">IRAS 07598+6508</span> Quasar in the constellation Camelopardalis

IRAS 07598+6508 known as IRAS F07599+6508, is a quasar located in the constellation of Camelopardalis. It is located 2.37 billion light years from Earth and is classified as both an ultraluminous infrared galaxy and a Seyfert galaxy.

References

  1. ↑ "Your NED Search Results". ned.ipac.caltech.edu. Retrieved 2024-05-20.
  2. 1 2 3 4 5 6 7 8 9 "Host Galaxy of QSO I Zw 1". iopscience.iop.org. arXiv: astro-ph/9801061 . doi:10.1086/305714 . Retrieved 2024-05-20.
  3. 1 2 3 "0050+124". quasar.square7.ch. Retrieved 2024-05-20.
  4. ↑ Condon, J. J.; Hutchings, J. B.; Gower, A. C. (1985-09-01). "HI emission from quasar host galaxies". The Astronomical Journal. 90: 1642–1647. Bibcode:1985AJ.....90.1642C. doi:10.1086/113870. ISSN   0004-6256.
  5. ↑ Buson, L. M.; Ulrich, M. -H. (1990-12-01). "The Ly-alpha and C IV lines in 10 low-redshift active galactic nuclei/quasars". Astronomy and Astrophysics. 240: 247. Bibcode:1990A&A...240..247B. ISSN   0004-6361.
  6. ↑ Usher, P. D.; Shen, B. S. P.; Barrett, J. W. (1971-05-01). "I ZW 1: a Variable Compact Galaxy". The Astrophysical Journal. 165: 647. Bibcode:1971ApJ...165..647U. doi:10.1086/150930. ISSN   0004-637X.
  7. ↑ Osterbrock, Donald E.; Martel, Andre (1993-09-01). "Spectroscopic Study of the CfA Sample of Seyfert Galaxies". The Astrophysical Journal. 414: 552. Bibcode:1993ApJ...414..552O. doi:10.1086/173102. ISSN   0004-637X.
  8. ↑ Gallo, L. C.; Boller, Th; Brandt, W. N.; Fabian, A. C.; Vaughan, S. (2004-04-01). "I Zw 1 observed with XMM-Newton - Low-energy spectral complexity, iron lines, and hard X-ray flares". Astronomy & Astrophysics. 417 (1): 29–38. arXiv: astro-ph/0312298 . Bibcode:2004A&A...417...29G. doi:10.1051/0004-6361:20034411. ISSN   0004-6361.
  9. ↑ Panda, Swayamtrupta; Santos, Denimara Dias dos (2021-11-29), "Revisiting the spectral energy distribution of I Zw 1 under the CaFe Project", Acta Astrophysica Taurica, 3 (1): 27, arXiv: 2111.01521 , Bibcode:2022AcAT....3a..27P, doi:10.31059/aat.vol3.iss1.pp27-34
  10. ↑ Kruper, J. S.; Urry, C. M.; Canizares, C. R. (1990-10-01). "Soft X-Ray Properties of Seyfert Galaxies. I. Spectra". The Astrophysical Journal Supplement Series. 74: 347. Bibcode:1990ApJS...74..347K. doi:10.1086/191503. ISSN   0067-0049.
  11. ↑ Boller, T.; Brandt, W. N.; Fink, H. (1996-01-01). "Soft X-ray properties of narrow-line Seyfert 1 galaxies". Astronomy and Astrophysics. 305: 53. arXiv: astro-ph/9504093 . Bibcode:1996A&A...305...53B. ISSN   0004-6361.
  12. ↑ Véron-Cetty, M.-P.; Joly, M.; Véron, P. (2004-04-01). "The unusual emission line spectrum of I Zw 1". Astronomy & Astrophysics. 417 (2): 515–525. arXiv: astro-ph/0312654 . Bibcode:2004A&A...417..515V. doi:10.1051/0004-6361:20035714. ISSN   0004-6361.
  13. ↑ Scharwächter, J.; Eckart, A.; Pfalzner, S. (2001-01-01). "Merger Properties of the Narrow-line Seyfert 1 Galaxy I Zw 1". Astronomische Gesellschaft Meeting Abstracts. 18: MS 05 22. Bibcode:2001AGM....18S0522S.
  14. ↑ Petrosian, Artashes; McLean, Brian; Allen, Ronald J.; MacKenty, John W. (2007-05-01). "Markarian Galaxies. I. The Optical Database and Atlas". The Astrophysical Journal Supplement Series. 170 (1): 33–70. Bibcode:2007ApJS..170...33P. doi:10.1086/511333. ISSN   0067-0049.
  15. ↑ Bothun, G. D.; Heckman, T. M.; Schommer, R. A.; Balick, B. (1984-09-01). "CCD imaging and neutral hydrogen emission in I ZW 1 and other low-redshift QSOs/AGNs". The Astronomical Journal. 89: 1293–1299. Bibcode:1984AJ.....89.1293B. doi:10.1086/113627. ISSN   0004-6256.
  16. ↑ Hutchings, J. B.; Crampton, D. (1990-01-01). "Images and Off-Nuclear Spectroscopy of QSOs". The Astronomical Journal. 99: 37. Bibcode:1990AJ.....99...37H. doi:10.1086/115309. ISSN   0004-6256.
  17. ↑ Barvainis, Richard; Alloin, Danielle; Antonucci, Robert (1989-02-01). "Detection of Strong Carbon Monoxide Emission from the Host Galaxy of the Quasar I ZW 1". The Astrophysical Journal. 337: L69. Bibcode:1989ApJ...337L..69B. doi:10.1086/185380. ISSN   0004-637X.
  18. 1 2 Eckart, A.; van der Werf, P. P.; Hofmann, R.; Harris, A. I. (1994-04-01). "Interstellar Medium and Star Formation in the Nearby QSO I ZW 1". The Astrophysical Journal. 424: 627. Bibcode:1994ApJ...424..627E. doi:10.1086/173919. ISSN   0004-637X.
  19. ↑ Guilloteau, S.; Delannoy, J.; Downes, D.; Greve, A.; Guelin, M.; Lucas, R.; Morris, D.; Radford, S. J. E.; Wink, J.; Cernicharo, J.; Forveille, T.; Garcia-Burillo, S.; Neri, R.; Blondel, J.; Perrigourad, A. (1992-09-01). "The IRAM interferometer on Plateau de Bure". Astronomy and Astrophysics. 262: 624. Bibcode:1992A&A...262..624G. ISSN   0004-6361.
  20. ↑ Weitzel, L.; Krabbe, A.; Kroker, H.; Thatte, N.; Tacconi-Garman, L. E.; Cameron, M.; Genzel, R. (1996-11-01). "3D: The next generation near-infrared imaging spectrometer". Astronomy and Astrophysics Supplement Series. 119 (3): 531–546. Bibcode:1996A&AS..119..531W. doi:10.1051/aas:1996266. ISSN   0365-0138.
  21. ↑ Buta, R.; Combes, F. (1996-01-01). "Galactic Rings". Fundamentals of Cosmic Physics. 17: 95–281. Bibcode:1996FCPh...17...95B.
  22. ↑ Genzel, R.; Weitzel, L.; Tacconi-Garman, L. E.; Blietz, M.; Cameron, M.; Krabbe, A.; Lutz, D.; Sternberg, A. (1995-05-01). "Infrared Imaging and Spectroscopy of NGC 7469". The Astrophysical Journal. 444: 129. Bibcode:1995ApJ...444..129G. doi:10.1086/175588. ISSN   0004-637X.
  23. ↑ Huang, Ying-Ke; Hu, Chen; Zhao, Yu-Lin; Zhang, Zhi-Xiang; Lu, Kai-Xing; Wang, Kai; Zhang, Yue; Du, Pu; Li, Yan-Rong; Bai, Jin-Ming; Ho, Luis C.; Bian, Wei-Hao; Yuan, Ye-Fei; Wang, Jian-Min (2019-05-08). "Reverberation Mapping of the Narrow-line Seyfert 1 Galaxy I Zwicky 1: Black Hole Mass". The Astrophysical Journal. 876 (2): 102. arXiv: 1904.06146 . Bibcode:2019ApJ...876..102H. doi: 10.3847/1538-4357/ab16ef . ISSN   0004-637X.
  24. ↑ Staff, News (2021-07-30). "Astronomers Detect Light Echoes Coming from Behind Supermassive Black Hole | Astronomy | Sci-News.com". Sci.News: Breaking Science News. Retrieved 2024-05-20.{{cite web}}: |first= has generic name (help)
  25. ↑ Wilkins, D. R.; Gallo, L. C.; Costantini, E.; Brandt, W. N.; Blandford, R. D. (2021-07-29). "Light bending and X-ray echoes from behind a supermassive black hole". Nature. 595 (7869): 657–660. arXiv: 2107.13555 . Bibcode:2021Natur.595..657W. doi:10.1038/s41586-021-03667-0. ISSN   0028-0836. PMID   34321670.
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