extragalactic planet

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. Later, two other similar populations were 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. These objects also could be a mix of low-mass rogue planets and primordial black holes.

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.{{Cite magazine |magazine=New Scientist |issue=2037 |url=https://www.newscientist.com/article/mg15120372.600-science--do-alien-worlds-throng-faraway-galaxy/ |title=Do alien worlds throng faraway galaxy? |first=Govert |last=Schilling |date=6 July 1996}}Extrasolar Visions, [http://www.extrasolar.net/planettour.asp?PlanetID=74 "The Q0957+561 Planet"] {{webarchive|url=https://web.archive.org/web/20120330100014/http://www.extrasolar.net/planettour.asp?PlanetID=74 |date=2012-03-30 }} (accessed 1 September 2009)

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.{{Cite web |url=http://www.thaindian.com/newsportal/health/first-extragalactic-exoplanet-may-have-been-found-by-gravitational-microlensing_100203542.html |title=First extragalactic exoplanet may have been found by gravitational microlensing |date=11 June 2009 |work=Thaindian News |archive-url=https://web.archive.org/web/20090624000150/http://www.thaindian.com/newsportal/health/first-extragalactic-exoplanet-may-have-been-found-by-gravitational-microlensing_100203542.html |archive-date=2009-06-24}}{{Cite web |work=New Scientist |url=https://www.newscientist.com/article/dn17287-first-extragalactic-exoplanet-may-have-been-found/ |title=First extragalactic exoplanet may have been found |date=10 June 2009 |first=Stephen |last=Battersby}}

In 2016, a tidal disruption event was detected on the {{Solar mass|9,150,000}} supermassive black hole IGR J12580+0134, which was caused by the destruction of a {{val|8|-|40|ul=Jupiter mass}} object by the black hole. IGR J12580+0134 is 17 million parsecs (55 million light-years) away from Earth.{{Cite journal |last1=Lei |first1=Wei-Hua |last2=Yuan |first2=Qiang |last3=Zhang |first3=Bing |last4=Wang |first4=Daniel |date=December 2015 |title=Igr J12580+0134: The First Tidal Disruption Event with an Off-Beam Relativistic Jet |journal=The Astrophysical Journal |language=en |volume=816 |issue=1 |pages=20 |doi=10.3847/0004-637X/816/1/20 |doi-access=free |issn=0004-637X|arxiv=1511.01206 }}

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, which consists of a stellar remnant (either a neutron star or a black hole) and a massive star, likely a B-type supergiant. The planet is {{Jupiter radius|0.7}} or around 50,000 kilometers in radius. {{cite web | url=https://exoplanet.eu/catalog/m51_uls_1_b--7496 | title=Planet M51-ULS-1 B | date=2020 }} and orbit at a distance of some tens of AU.{{cite news|last=Crane|first=Leah|date=23 September 2020|title=Astronomers may have found the first planet in another galaxy|work=New Scientist|url=https://www.newscientist.com/article/2255431-astronomers-may-have-found-the-first-planet-in-another-galaxy/|access-date=25 September 2020}} The study of M51-ULS-1b as the first known extragalactic planet candidate was published in Nature in October 2021.{{Cite journal|last1=Di Stefano|first1=Rosanne|last2=Berndtsson|first2=Julia|last3=Urquhart|first3=Ryan|last4=Soria|first4=Roberto|last5=Kashyap|first5=Vinay L.|last6=Carmichael|first6=Theron W.|last7=Imara|first7=Nia|date=2021-10-25|title=A possible planet candidate in an external galaxy detected through X-ray transit|url=https://www.nature.com/articles/s41550-021-01495-w|journal=Nature Astronomy|volume=5 |issue=12 |language=en|pages=1297–1307|arxiv=2009.08987|doi=10.1038/s41550-021-01495-w|bibcode=2021NatAs...5.1297D |s2cid=256726097 |issn=2397-3366}}

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.{{cite journal|last1=Reggiani|first1=Henrique|last2=Meléndez|first2=Jorge|title=Evidences of extragalactic origin and planet engulfment in the metal-poor twin pair HD 134439/HD 134440|journal=Monthly Notices of the Royal Astronomical Society|date=December 1, 2018|volume=475|issue=3|pages=3502–3510|doi=10.1093/mnras/sty104|doi-access=free |url=https://academic.oup.com/mnras/article-abstract/475/3/3502/4803967?redirectedFrom=fulltext|accessdate=10 May 2018|language=en|issn=0035-8711|arxiv=1802.07469|bibcode=2018MNRAS.475.3502R}}

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.{{cite journal | title=A dynamical investigation of the proposed BD +20 2457 system |author1=Horner, J. |author2=Wittenmyer, R. A. |author3=Hinse, T. C. |author4=Marshall, J. P. | journal=Monthly Notices of the Royal Astronomical Society|year=2014|volume=439|issue=1|pages=1176–1181|arxiv=1401.2793|bibcode=2014MNRAS.439.1176H|doi=10.1093/mnras/stu081|doi-access=free |s2cid=54534748 }} 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.{{Cite journal |last1=Perottoni |first1=Hélio D. |last2=Amarante |first2=João A. S. |last3=Limberg |first3=Guilherme |last4=Rocha-Pinto |first4=Helio J. |last5=Rossi |first5=Silvia |last6=Anders |first6=Friedrich |last7=Borbolato |first7=Lais |date=May 2021 |title=Searching for Extragalactic Exoplanetary Systems: The Curious Case of BD+20 2457 |journal=The Astrophysical Journal |volume=913 |issue=1 |pages=L3 |doi=10.3847/2041-8213/abfb06 |doi-access=free |arxiv=2104.08306 |bibcode=2021ApJ...913L...3P |issn=0004-637X}}

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,{{cite news|url=http://www.eso.org/public/news/eso1045/|title=Planet from another galaxy discovered|date=18 November 2010|access-date=17 November 2011|newspaper=ESO Press Release}} 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.

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. 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).

• {{annotated link|Exoplanet}}
• {{annotated link|Solar System planets}}
• Extragalactic astronomy – the study of any objects outside the Milky Way including the extragalactic planets

{{reflist

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{{cite arXiv |last=Di Stefano |first=R. |display-authors=etal |eprint=2009.08987 |title=M51-ULS-1b: The First Candidate for a Planet in an External Galaxy |class=astro-ph.HE |date=18 September 2020}}

}}

• [https://www.staringup.com/posts/exoplanet-found-in-another-galaxy-around-powerful-x-ray-source/ Extragalactic planet candidate around high-mass X-ray binary M51-ULS-1] from Staringup in September 2020.

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Category:Types of planet

Category:Exoplanetology

Category:Extragalactic astronomy