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Extragalactic planet

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An extragalactic planet, also known as an extragalactic exoplanet or an extroplanet,[1][2][3] is a star-bound planet or rogue planet located outside of the Milky Way Galaxy. Due to the immense distances to such worlds, they would be very hard to detect directly. However, indirect evidences suggest that such planets exist.[4][5][6][7][8] Nonetheless, the most distant confirmed planets are SWEEPS-11 and SWEEPS-04, located in Sagittarius, approximately 27,710 light-years from the Sun, while the Milky Way is about 87,400 light-years in diameter. This means that even galactic planets located further than that distance have not been detected.

Candidate extragalactic planets

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Candidates from gravitational microlensing

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A microlensing event in the Twin Quasar gravitational lensing system was observed in 1996, by R. E. Schild, in the "A" lobe of the lensed quasar. It is predicted that a 3-Earth-mass planet in the lensing galaxy, YGKOW G1, caused the event. This was the first extragalactic planet candidate announced. This, however, is not a repeatable observation, as it was a one-time chance alignment. This predicted planet lies 4 billion light years away.[9][10]

PA-99-N2 b

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A team of scientists has used gravitational microlensing to come up with a tentative detection of an extragalactic exoplanet in Andromeda, the Milky Way's nearest large galactic neighbor. The lensing pattern fits a star with a smaller companion, PA-99-N2, weighing just around 6.34 times the mass of Jupiter. This suspected planet is the first announced in the Andromeda Galaxy.[11][12]

Evidences of populations of rogue planets

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A population of unbound planets between stars, with masses ranging from Lunar to Jovian masses, was indirectly detected, for the first time, by astrophysicists from the University of Oklahoma in 2018, in the lensing galaxy that lenses quasar RX J1131-1231 by microlensing.[4][5][6] Later, two other similar populations were indirectly detected in the galaxies of the galaxy-quasar lensing systems Q J0158-4325 and SDSS J1004+4112, whose foreground members are 3.6 billion and 6.3 billion light-years away, respectively.[7][8]

Candidates around extragalactic black-holes and X-ray binaries

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IGR J12580+0134 b

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In 2016, a candidate planet was found orbiting a 9,150,000 M☉ supermassive black hole,[13] indicating that it might be a blanet. IGR J12580+0134 b could be a brown dwarf or planet as it has a mass of 8–40 MJ. Since IGR J12580+0134 b is located near the center of the NGC 4845 galaxy, it is 17 million parsecs (55 million light-years) away.[14]

M51-ULS-1b

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In September 2020, the detection of a candidate planet orbiting the high-mass X-ray binary M51-ULS-1 in the Whirlpool Galaxy was announced. The planet was detected by eclipses of the X-ray source,[1] which consists of a stellar remnant (either a neutron star or a black hole[2]) and a massive star, likely a B-type supergiant. The planet is 0.7 RJ in size or around 50,000 kilometers in radius. [15] and orbit at a distance of some tens of AU.[16][17] The study of M51-ULS-1b as the first known extragalactic planet candidate was published in Nature in October 2021.[18]

Candidates around formerly extragalactic stars

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Disrupted planets of runaway stars

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The subdwarf star HD 134440, which is currently located in galactic halo and has extragalactic origin, was found to have a significantly higher metallicity than the similar star HD 134439. In 2018, this was believed to resulted from an engulfment of orbiting planets by HD 134440.[19]

BD+20 2457 b and BD+20 2457 c

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The bright giant star BD+20 2457 was proposed to host two super-Jupiter planets or brown dwarfs, although the claimed planetary system is not dynamically stable.[20] As BD+20 2457 is a halo star possibly having formed in the Gaia Enceladus, which are galactic remains of a former galaxy, the star and its planets might be extragalactic in origin.[21]

Refuted extragalactic planets

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HIP 13044 b

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A planet with a mass of at least 1.25 times that of Jupiter had been potentially discovered by the European Southern Observatory (ESO) orbiting a star of extragalactic origin, even though the star currently has been absorbed by our own galaxy. HIP 13044 is a star about 2,000 light years away in the southern constellation of Fornax,[22] part of the Helmi stream of stars, a leftover remnant of a small galaxy that collided with and was absorbed by the Milky Way over 6 billion years ago.[23]

However, subsequent analysis of the data revealed problems with the potential planetary detection: for example an erroneous barycentric correction had been applied (the same error had also led to claims of planets around HIP 11952 that were subsequently refuted). After applying the corrections, there is no evidence for a planet orbiting the star.[24] If it had been real, the Jupiter-like planet would have been particularly interesting, orbiting a star nearing the end of its life and seemingly about to be engulfed by it, potentially providing an observational model for the fate of our own planetary system in the distant future (cf. Future of Earth).

See also

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References

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  1. ^ a b Smith, Kiona (26 October 2021). "Extroplanet: Astronomers may have just found the first planet outside our galaxy". Inverse. Retrieved 2021-11-08.
  2. ^ a b Planet Song M51 ULS 1b Messier 51 Whirlpool Galaxy, 6 November 2021, retrieved 2021-11-08
  3. ^ Sandhya Ramesh (2021-10-29). "NASA telescope may have just helped find the first planet spotted outside Milky Way". ThePrint. Retrieved 2021-11-08.
  4. ^ a b Dai, Xinyu; Guerras, Eduardo (2 February 2018). "Probing Planets in Extragalactic Galaxies Using Quasar Microlensing". The Astrophysical Journal. 853 (2): L27. arXiv:1802.00049. Bibcode:2018ApJ...853L..27D. doi:10.3847/2041-8213/aaa5fb. S2CID 119078402.
  5. ^ a b Zachos, Elaine (5 February 2018). "More Than a Trillion Planets Could Exist Beyond Our Galaxy - A new study gives the first evidence that exoplanets exist beyond the Milky Way". National Geographic Society. Archived from the original on February 5, 2018. Retrieved 5 February 2018.
  6. ^ a b Mandelbaum, Ryan F. (5 February 2018). "Scientists Find Evidence of Thousands of Planets in Distant Galaxy". Gizmodo. Retrieved 5 February 2018.
  7. ^ a b Bhatiani, Saloni; Dai, Xinyu; Guerras, Eduardo (November 2019). "Confirmation of Planet-mass Objects in Extragalactic Systems". The Astrophysical Journal. 885 (1): 77. arXiv:1909.11610. Bibcode:2019ApJ...885...77B. doi:10.3847/1538-4357/ab46ac. ISSN 0004-637X.
  8. ^ a b Lazaro, Enrico de (November 2019). "Free-Floating Planet-Mass Objects are Common in Galaxies | Sci.News". Sci.News: Breaking Science News. Retrieved 2024-11-17.
  9. ^ Schilling, Govert (6 July 1996). "Do alien worlds throng faraway galaxy?". New Scientist. No. 2037.
  10. ^ Extrasolar Visions, "The Q0957+561 Planet" Archived 2012-03-30 at the Wayback Machine (accessed 1 September 2009)
  11. ^ "First extragalactic exoplanet may have been found by gravitational microlensing". Thaindian News. 11 June 2009. Archived from the original on 2009-06-24.
  12. ^ Battersby, Stephen (10 June 2009). "First extragalactic exoplanet may have been found". New Scientist.
  13. ^ Martin, Pierre-Yves (2016). "Planet IGR J12580+0134 b". exoplanet.eu. Retrieved 2024-10-16.
  14. ^ Lei, Wei-Hua; Yuan, Qiang; Zhang, Bing; Wang, Daniel (December 2015). "Igr J12580+0134: The First Tidal Disruption Event with an Off-Beam Relativistic Jet". The Astrophysical Journal. 816 (1): 20. arXiv:1511.01206. doi:10.3847/0004-637X/816/1/20. ISSN 0004-637X.
  15. ^ "Planet M51-ULS-1 B". 2020.
  16. ^ Di Stefano, R.; et al. (18 September 2020). "M51-ULS-1b: The First Candidate for a Planet in an External Galaxy". arXiv:2009.08987 [astro-ph.HE].
  17. ^ Crane, Leah (23 September 2020). "Astronomers may have found the first planet in another galaxy". New Scientist. Retrieved 25 September 2020.
  18. ^ Di Stefano, Rosanne; Berndtsson, Julia; Urquhart, Ryan; Soria, Roberto; Kashyap, Vinay L.; Carmichael, Theron W.; Imara, Nia (2021-10-25). "A possible planet candidate in an external galaxy detected through X-ray transit". Nature Astronomy. 5 (12): 1297–1307. arXiv:2009.08987. Bibcode:2021NatAs...5.1297D. doi:10.1038/s41550-021-01495-w. ISSN 2397-3366. S2CID 256726097.
  19. ^ Reggiani, Henrique; Meléndez, Jorge (December 1, 2018). "Evidences of extragalactic origin and planet engulfment in the metal-poor twin pair HD 134439/HD 134440". Monthly Notices of the Royal Astronomical Society. 475 (3): 3502–3510. arXiv:1802.07469. Bibcode:2018MNRAS.475.3502R. doi:10.1093/mnras/sty104. ISSN 0035-8711. Retrieved 10 May 2018.
  20. ^ Horner, J.; Wittenmyer, R. A.; Hinse, T. C.; Marshall, J. P. (2014). "A dynamical investigation of the proposed BD +20 2457 system". Monthly Notices of the Royal Astronomical Society. 439 (1): 1176–1181. arXiv:1401.2793. Bibcode:2014MNRAS.439.1176H. doi:10.1093/mnras/stu081. S2CID 54534748.
  21. ^ Perottoni, Hélio D.; Amarante, João A. S.; Limberg, Guilherme; Rocha-Pinto, Helio J.; Rossi, Silvia; Anders, Friedrich; Borbolato, Lais (May 2021). "Searching for Extragalactic Exoplanetary Systems: The Curious Case of BD+20 2457". The Astrophysical Journal. 913 (1): L3. arXiv:2104.08306. Bibcode:2021ApJ...913L...3P. doi:10.3847/2041-8213/abfb06. ISSN 0004-637X.
  22. ^ "Planet from another galaxy discovered". ESO Press Release. 18 November 2010. Retrieved 17 November 2011.
  23. ^ Klement, R.; Setiawan, J.; Thomas Henning; Hans-Walter Rix; Boyke Rochau; Jens Rodmann; Tim Schulze-Hartung; MPIA Heidelberg; ESTEC (2011). "The visitor from an ancient galaxy: A planetary companion around an old, metal-poor red horizontal branch star". The Astrophysics of Planetary Systems: Formation, Structure, and Dynamical Evolution. IAU Symposium. Vol. 276. Proceedings of the International Astronomical Union. pp. 121–125. arXiv:1011.4938. Bibcode:2011IAUS..276..121K. doi:10.1017/S1743921311020059.
  24. ^ Jones, M. I.; Jenkins, J. S. (2014). "No evidence of the planet orbiting the extremely metal-poor extragalactic star HIP 13044". Astronomy & Astrophysics. 562: id.A129. arXiv:1401.0517. Bibcode:2014A&A...562A.129J. doi:10.1051/0004-6361/201322132. S2CID 55365608.
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